Birty Dastards Jeep Club
Tech Forum => Workshop => Topic started by: bill99 on November 01, 2015, 01:53:59 AM
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I have a 1999 XJ Cherokee 4 litre with a (check engine) light on but also a bit of a twist.
As mentioned the check engine light is now permanently on and the car will start and run at idle just fine but as we drive away and the engine revs pick up suddenly bam everything cuts out, no stutter or lack of power from petrol starvation or something like that just everything off as if I had just turned off the key.
I can then start it up again just fine and run along only using idle revs or just above idle, basically in first gear, I think that’s a bit beyond limp mode.
The fact that it starts first turn of the key suggests the basics are all there, fuel / spark etc.
Any help to point me to the right area appreciated, I don’t have an error code reader and not much luck getting someone to look at it.
Cheers
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You can read your error codes on your odometer.
Turn the ignition key on, off, on, off and on. The codes will be displayed in sequence. 55 means all codes have been displayed.
Sounds like a sensor, possibly TPS (Throttle Position Sensor)
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The tps won't show up as a fault code.
But it sounds like it could be a duff battery as the jeep been left standing?
Where are you based
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Does it rev freely when standing still in Neutral? If it does I would check for loose/damaged wiring.
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Thanks for all the replies.
The jeep is a daily driver and has been great for the last 5 years with just with basic servicing and one incident with the crank position sensor just needing the connector cleaned. I live in West Lothian near Edinburgh.
Today I got into it and did a general fluids check and removed the air intake to get access to the cable loom and checked all around the engine bay but nothing obvious. The battery is good and spins the engine over fine.
Anyway I cleaned the crank sensor again just because I had good access to it.
Also disconnected the battery to re-set the CPU and took it for a run.
Now it will run better I can drive it almost normal but the engine does cut out sometimes just breaking for a junction. The check engine light is still on.
I cant seem to get the on off /on off / on to work and display the error codes.
I will take it out for a longer run later to see if the CPU can learn its setting and deal with the cut outs.
I have got a guy in the motor trade asking around if someone can do a plug in diagnosis locally. There was one place that could do it but they did not have enough demand for it to justify renewing the software licence. I find Jeep main dealers around here are not interested in old cars and make you feel like a leper, not to mention the costs.
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I cant seem to get the on off /on off / on to work and display the error codes.
Have a look here http://www.jeep-xj.info/HowtoECUcodes.htm it may explain it better than I did.
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It has OBDII, any garage will have a scanner capable of reading it.
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Thanks Mike and thanks General confusion for that link to the error code list.
Time to buy myself a scanner.
By the way I have tried every combination of key on/off and trip meter switching as per that link and all I ever get is a system check of the instrument panel but no codes.
Shame you cant just connect up a serial port on a laptop and run a bit of software, or can you?
Cheers
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you can but its supplied by jeep and an obvious licence cost to go with it
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Just for the record, having tried for ages myself in my '98 XJ, I researched some more and found that the key on-off trick doesn't seem to work after '97.
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if you have an adriod phone
have a look at this
https://play.google.com/store/apps/details?id=org.prowl.torque&hl=en
and get one of these
http://www.ebay.co.uk/itm/ELM327-ODB2-ODB-II-Wireless-Bluetooth-Car-Auto-Diagnostic-Scan-Tool-Scanner-BF-/351361606924?hash=item51cec8a50c:g:aLIAAOSwFnFV952x
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yeah found some of those on ebay last night and i think i am going to order one that works on a usb adapter cable with any windows pc from XP onwards.
In the mean time i see a basic hand held Maxi Scan unit in a local auto shop for £35 that will do for now just to get started and get the error codes off and move forward, i will try to get there and pick one up tomorrow.
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Got a cheap £35 scan tool and it shows generic OBD-2 codes as opposed to what to expect from the jeep onboard codes.
Generic code is P0123, which is listed as (TPS/Pedal Position sensor A Circuit High Input).
So I had a clean and re-seat of all the connecters around the throttle body but no luck.
Guess I will have to track down a circuit diagram and check out the cables.
Question before I get into that are these position sensors known to go faulty or is a cable fault more likely.
Also just wondering when the fault is finally corrected will the check engine light go out or will it need to be re-set?
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TPS do go. Cheap replacements are not always great. Before stumping out for a genuine Mopar one you can test the sensor with a multimeter. Connect to the signal wire and move the throttle position from 0 - full throttle and see the voltage steadily change. Alternatively borrow a good genuine one or get a genuine one from a good scrapper.
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:iagree:
if its the original then it's not water proofed and they get damp inside
the new mopar ones are sealed better
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Have a look at this :
http://troubleshootmyvehicle.com/jeep/4.0L/asd-relay-wiring-diagram
It's the Auto Shut Down device kicking in from the sound of it, mine has been doing the same for a week now, since getting it back from the MoT station where they welded the drivers side sill/floorpan area. Obviously they had to lift the carpets so the seat, sill trim etc had to come out including the kick panel trim. I can get the kickpanel out without disturbing the lower dash which holds the fusebox but obviously they couldn't. This means the lower dash was left hanging with the fusebox pulling on the wiring. It's pulled several connectors "out" - not all the way out so it's obvious but partially out so they no longer make proper contact. I've been pushing the fuses back in one by one while pushing the connectors back in with a thin screwdriver.
Obviously most of the info on the ASD shows the underbonnet fusebox (PDC) and i'm referring to the underdash fusebox but there are some feeds from it to the PCM and other things. As that was what was disturbed in mine that's where i'm concentrating my efforts. However, yours could just be a dirty fuse in the PDC or something of that sort.
Worth checking out maybe?
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Hi Lairdscooby, yeah mine was like that at first but after taking the battery off the CPU for a while and starting over it seemed to learn to deal with the bad TPS and actually drives not too bad now and only cuts out when slowing for junctions.
But I must say when you are doing a bit of speed and everything cuts off including all the power-assisted brakes and steering it is a bit of a shock.
I’ve got a cheap TPS on order just to eliminate it so I can move another bit forward.
Cheers
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Funny you should mention disconnecting the battery effecting a cure Bill - i've also had a similar experience. Although that almost sounds like a contradiction in what i said earlier, it does make sense when you know the sequence of events on mine.
Firstly i should say mine has LPG - a single point mixer system.
Four weeks ago i put it in for MoT and it failed on welding and emissions. The emissions i knew about, the stepper motor for the LPG had siezed in the en position so it was running rich. At some point someone has fitted a power valve to the mixer so i was able to tweak it down to 2% (a pass on LPG) which is still richer than ideal but a compromise to ensure it doesn't go lean at high revs. However, this would often cause the engine to die on a trailing throttle approaching a bend or junction - very embarassing and quite a shock the first time the steering goes heavy!
Anyway, when i got the car back, it wouldn't run on LPG as in the ECU wouldn't change over. Basically the LPG ECU had died while at the MoT station. I thought it was simply a wiring problem because of them pulling the fusebox down but no. Luckily i had another (different make) LPG ECU which i had bought to convert one of my Rovers. So i fitted this, it now runs better but still cuts out occasionally due to the over-rich idle but i haven't got the programming software working yet - another story, long and boring one!
Anyhow, the system was showing a Lambda fault because of the old LPG ECU so i disconnected the battery to reset the PCM. This has cured the ASD coming in. All because of an apparent Lambda fault which is no more because it was down to a FUBAR LPG ECU!
Today i finally found (and thought i had fixed) the last (i hope!) fault caused by the dash hanging on the fusebox - the heater switch! AMazingly the weight of the dash hanging had pulled so much on the loom that it had yanked on the cables that go to the heater control panel, in particular the switch that operates the fan and air con, breaking the mounting legs! This meant the switch "fell off" the temperature control part leaving no fan at all or direction control. I superglued it back together but the glue was past its best so broke again in short order. Fortunately i made sure it didn't go to the "OFF" position at any point so i still have the fan and heat coming through the screen and footwell with a little out of the vent.
There is a point to all this waffle - now it's running right, when the new TPS arrives don't fit it until the fault comes back or you could be chasing your tail as i was for a few days simply because there were several faults with similar symptoms. Hopefully you only have the one fault and have fixed it - if yours had a dodgy lambda and the PCM wasn't reset after renewing it, this could have caused your problems.
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Well I got my new TPS and fitted it today and nothing changed so out with the code reader and cleared the error codes but it comes straight back on as 0123 the A circuit is high.
OK so battery off and reset codes again but it comes straight back on, so I took it for a drive to see if it would learn and sort itself out but no luck.
So out with the voltmeter and splice in a test cable to check the TPS in circuit and it seems to be working fine to me. It varies smoothly from 1.3volts to 4,8volts and the earth cable checks out fine and the 5-volt supply is fine.
Interestingly while I had the 3-pin cable off the TPS to measure the voltage off load the CPU detected a 0122 error, which is for a low circuit, which yes it is due to the cable being off. So the CPU must be getting the signal feed ok because it can detect both high and low errors so that should eliminate any cable short or open circuit from the TPS to the CPU.
So ok I checked the old TPS on a bench rig with 5 volts supply and it works fine but because it is on the bench and the throttle mechanical connection is not there it goes right down to 0.1 volt and up to 4.8 volts. So it looks like that was always ok to start with.
So now I am stuffed I really don’t know where to go next because it detects a TPS error and shows the symptoms of a TPS error but I cant see anything wrong here.
Am I missing something here, does the TPS just get fitted and go or is there some set-up procedure.
I’m grasping at straws here but could it be a mechanical issue with the throttle mechanism holding it slightly open and giving 1.3 volts instead of allowing it to fully turn right down to 0.1volts. As far as I can see the operating blade is in the correct position.
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Check the earth point for the PCM. I think it's somewhere near the L/H headlamp and you'll probably have to remove the PCM (and before that, the battery) to do it. I had something similar on mine where it was telling me the Lambda sensor was U/S and it was running high emissions on both LPG and petrol and it turned out to be the earth point near the oil filter on the engine block - removed the nut, cleaned the ring terminals and the block/nut etc, refitted and problem solved! That is the earth for the Lambda ssensor strangely as the sensor is the other side of the engine.
Also check the earth for the TPS just to be on the safe side.
Basically the PCM will see an extra low voltage from most sensors if it has a bad earth and if the sensor has a bad earth, the PCM will see an extra high voltage from the sensor. This could only be something like 0.1 or 0.2 volts but that might be high enough to throw things into confusion.
There probably is a set-up procedure for the TPS but it might pay to make sure the throttle butterfly is shutting properly first. There is an electronic bypass for the idle speed/fast idle and the butterfly only supplies enough air for the basic idle speed which is usually lower than the correct idle speed.
Things that might stop the throttle shutting - over-tight throttle or kickdown (or cruise control) cable, someone has been messing with the throttle stop screw, gunge from blow by from the PCV system build up on the butterfly.
All basic stuff that's often overlooked.
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Typical values for TJ/XJ TPS are .6-.8V at idle and 3.6-3.9 at WOT. Yours seem a bit off from that and more like what would be seen from the TPS in a ZJ.
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Thanks for all the help so far guys.
I have swapped back to my old TPS and checked the output to see if I have anything different from the replacement and it is pretty much identical.
The TPS signal is 1,2-volt / 4-volts.
I am coming round to the idea that this is somehow mechanical, when I fit the TPS and slide the bolts in it has to twist just enough to turn it up to 1,2 volts even though the throttle butterfly is completely closed and you can hear it physically close. If the CPU is looking for 0.1 volts then 1.2 volts could be considered as high and produce the error C0123 which is TPS A circuit high.
The thing is you can’t fit it any other way so I can’t adjust it. Can anyone who has fitted a TPS in the past confirm that it is normal to have to give it a bit of a biased on twist to get the bolts in?
Anyway I have also cleaned and checked all the earth points around the CPU and checked all the pins on the CPU for corrosion but all is well there. For good measure I have also run an additional earth wire back to the battery.
That’s me for tonight will get back to it tomorrow.
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I went through this and it eventually got really bad and finally undriveable. Turned out to be the MAP sensor and fitting a known good one, genuine one off a scrapper fixed it instantly. Handy if you know a garage with this option near you.
And yes TPS needs a bit of a twist to line up and fit screws.
Where are you?
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hi james thanks for that confirmation about the twist of the TPS when fitting,that was bugging me.
I’m in West Lothian near Edinburgh.
I went to the big scrappy in the area (Sports car Breakers) and not a single jeep, I had planned to basically take off all the sensors.
did your MAP sensor not get a error report?
cheers
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I went through this and it eventually got really bad and finally undriveable. Turned out to be the MAP sensor and fitting a known good one, genuine one off a scrapper fixed it instantly. Handy if you know a garage with this option near you.
And yes TPS needs a bit of a twist to line up and fit screws.
Where are you?
That's really interesting - although i thought mine was cured of cutting out because of the fusebox troubles and the ASD kicking in, it seems to cut out every so often but fortunately for me, when it does the LPG takes over. I can still hear the clicking of the ASD relay every so often but it keeps going on gas.
That said i do want it completely sorted so i might have to look at the MAP sensor as well.
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I had rough running which then got worse and worse until undriveable. Eventually the check engine light came on but only after it was clearly a major problem. I had it scanned at a local Jeep specialist but only with a normal garage scanner and not a Jeep specific setup. They put on a MAP sensor and it was fixed.
Prior to that I had changed TPS, all the ignition parts, checked for air leaks and exhaust leaks, changed fuel pump and still not quite fixed the problem. All of these things can cause running problems.
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Hmm, best i look at the MAP sensor then. I've got a few non-Jeep MAP sensors floating around, if it comes to it i'll adapt one of those but i'll see if i can find a Jeep one first.
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So I got a MAP sensor and fitted that but no real improvement so I draw a blank there.
Anyway I got into the cable loom with a meter and checked all the continuity from the TPS to the PCM unit and checked out the internal sensors earth link in the PCM as well, Pin-4.
It was while doing all this I realised the TPS pin (23) was sitting at 5-volts when the 3 pin connecter was off the TPS, in theory it should be low.
So check this out and sure enough it is sitting at 5-volts any time the power is on but as the TPS is normally connected the 5-volts is pulled down to 1.3-volts by the sensor ground.
So when you check the sensor output it appears to work but it’s really just the grounding effect rising as the throttle opens.
So to cut a long story short I need to replace the PCM unit as it seems to have an internal 5-volt short circuit on to pin 23 where the TPS signal should go in.
So any help on fitting a second hand PCM unit from a scrappy would be appreciated, I hear it is programmed to the sentinel system so it wont just plug and play. Can anyone give me an outline of what is required assuming I can get one.
Also it follows if anyone wants to sell one for 1999 XJ 4.0 L petrol send me a message.
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Hmm, i had a look at the diagram i have for the 93 XJ 4.0 which also applies to my 95 XJ 4.0 and the TPS signal pin is Pin 22, not Pin 23.
I can't imagine changing the loom, the plug and the PCM just for the sake of shifting one pine along so are you sure you mean Pin 23 or is that maybe a typo, misread the diagram or something?
On a more technical note, there's a good chance the PCM has an internal pull-up resistor for biasing the signal processing, whether it's via a DAC/ADC, an op-amp or whatever. This 5.0V at the signal pin when the TPS is effectively open circuit is not necessarily a fault in itself, it could even be used byu the PCM to indicate a fault condition.
Next technical question, did you reset the PCM by disconnecting the battery for a few minutes after fitting the replacement MAP sensor? If not then it may still register the fault (even though it's not showing) and still be in limp mode. If you haven't reset itthen it would be worth doing before jumping the gun and condemning the PCM out of hand.
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Hmm, i had a look at the diagram i have for the 93 XJ 4.0 which also applies to my 95 XJ 4.0 and the TPS signal pin is Pin 22, not Pin 23.
I can't imagine changing the loom, the plug and the PCM just for the sake of shifting one pine along so are you sure you mean Pin 23 or is that maybe a typo, misread the diagram or something?
On a more technical note, there's a good chance the PCM has an internal pull-up resistor for biasing the signal processing, whether it's via a DAC/ADC, an op-amp or whatever. This 5.0V at the signal pin when the TPS is effectively open circuit is not necessarily a fault in itself, it could even be used byu the PCM to indicate a fault condition.
Next technical question, did you reset the PCM by disconnecting the battery for a few minutes after fitting the replacement MAP sensor? If not then it may still register the fault (even though it's not showing) and still be in limp mode. If you haven't reset itthen it would be worth doing before jumping the gun and condemning the PCM out of hand.
Hi there yes definitely pin 23 for my TPS signal; (pin 22) on a 1998 onward seems to be called (fused B+) in the diagram. I also did the battery and cleared the codes with a reader.
On my 1999 the TPS is going into the PCM connecter block nearest the headlight on the pins as below.
5-volt supply = pin 17 (Orange wire)
Signal output = pin 23 (orange with blue stripe)
Ground = pin 4 (brown with yellow stripe)
Nothing would surprise me about Chrysler electrics after the battle I had to get to the transmission module under the dash, there was a possibility of that causing the 5-volts to appear on the TPS signal pin because that is shared with the Transmission control module.
You could be right about the 5-volts on the pin being a sense for errors or something, I have been looking for an internal circuit diagram of the PCM unit and a good operating description of it but no luck so far.
My PCM part number is P56041 494AD if I could pick one up and figure out how to frig the immobiliser and maybe other stuff I would give it a go just to see.
Cheers
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Trust Chrysler to fanny about with the pin numbers just for the sake of making the PCMs non-interchangeable! If you could PM me your diagram i'm fairly sure i could find the bypass points for the immobiliser (will need not just the PCM diagram but the complete car diagram too) so you could frig it - not happy about posting that on the open forum as it puts mine, yours and all the other members cars at increased risk.
Still not convinced the PCM or the TPS is at fault though but without looking deeper can't think what else. Mine behaved perfectly on a 200-ish mile round trip today until it got home and was idling on pterol after restarting and it cut out on the ASD. Restarted fine first time and then i blipped the throttle to get it back on gas - no troubles at all on that!
The pins on my PCM for the TPS (as far as i know, i'm going on the 93 diagram which i've been assured is the same as my 95 XJ) are :
4 Sensor earth - Black/L.Blue
6 Sensor 5V - Violent/White
22 Sensor signal - Orange/D.Blue
So.................. not only did they change the pinouts on the PCM but they changed the colour codes as well! Gits!
Could well be the TCU is causing the 5V pull up on the signal pin of the TPS but given that exctra information, i would expect the gearbox to do something odd with the shit patterns. Does your box shift normally? If so i'd hazard a guess the TPS is ok.
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I think they made a big upgrade around 1997 / 1998 so lots of parts would change, that also ties in with the first Grand Cherokee models.
Anyway i was looking at module locations on in the books and there is a sentinel module I was hoping to maybe just remove that to try a new PCM (wishfull thinking maybe).
with the replacement TPS doing the exact same issue and the TPS error code still coming straight back on after being erased I would still like to pick up a PCM just to try and eliminate it.
Cheers
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I think the upgrade/update/facelift was about 96/97 and i saw a P reg G/Cherokee today while out and about. That would be 96-97 registered so ties in with the facelift/upgrade etc.
I see where you're going with the PCM idea, i hadn't realised it was still throwing the TPS fault code after a reset.
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In the US vehicle electronics had to be OBDII in petrol models so a PCM redesign was required.
As far as the security on a 99 is concerned, the SKIM (Sentry Key Immobiliser Module) and PCM use rolling codes and both have the VIN programmed. If they do not recognise each other the system will not allow the engine to run for more than a few seconds. A PCM from the US, where SKIS (Sentry Key Immobiliser System) was optional, that did not have SKIS enabled would work. The SKIM needs disconnecting before the non SKIS PCM is connected or SKIS will auto enable in the non-SKIS PCM.
If you wanted to try a PCM from the UK you would also need it's corresponding SKIM.
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:imwitstupid:
What he said. Removing the module in the steering column won't be enough. A non SKIS PCM from the U.S. might be a good idea though, I don't think they are too pricey.
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All of that makes a lot of sense and explains the need to alter the pin-outs on the PCM - what would be the point of having the immobiliser if it could be bypassed by fitting an earlier (non-immobiliser) PCM. Annoying (for you and your problem) that it has the software immobilisation too (rolling codes etc) as that makes life harder.
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Thanks for all that about the immobiliser situation that explains why I see some jeep PCM’s on ebay that also include the remote key fob but it looks like I would also need the SKIS module as well.
Oh well if there is a way it may be an option if I get in quick when the right jeep comes into a scrappy and I can get everything from the same car of the right year.
I did read up a bit on the sentinel system and there seems to be a chip in the actual key as well so maybe I would need keys and the main steering column ignition lock as well.
Hmmm, a bit daunting.
Thanks Guys
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Sounds like a plan to find a complete runner in a scrappies - or keep your eyes peeled on ebay for a spares/repair car.
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Keys. Of course, they would be needed to match the SKIM. Forgot about that. It would be relatively easy to rekey your ignition barrel for the different keys if you did end up going that route.
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Bit of an update.
I got my XJ connected up to a professional diagnostic tool running Jeep software and sure enough it came up with the 0123 code of the TPS circuit high.
So this tool can monitor all the sensors and their voltages in real time so with the engine running we can see that the TPS signal never moves so the PCM cannot read the signal even though the multimeter shows it going up and down on the PCM connector pin when the throttle is opened.
All the other sensors read and change with engine revs, a really good tool it can measure all the supply and signal voltages to everything but it's £1500 plus on going software upgrades charges.
So that kind of does it, it seems that the PCM unit is faulty.
We are looking into a repair from a specialist to see what costs are but I have had a few warnings from people about an attempted repair making it worse.
Just wondering has anyone here ever had a repair done with good or bad results?
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Borrow another PCM (any '98-99 XJ or TJ one will do, plug it in, don't bother to try to start it, just do the same test again and see if it can see the TPS working. You'll have to ignore the SKIS errors it'll throw up, but it'll prove it isn't a weird wiring fault without the aggro of programming a new unit.
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Borrow another PCM (any '98-99 XJ or TJ one will do, plug it in, don't bother to try to start it, just do the same test again and see if it can see the TPS working. You'll have to ignore the SKIS errors it'll throw up, but it'll prove it isn't a weird wiring fault without the aggro of programming a new unit.
Well that's a good one Mike.
So in theory i could buy an American one off eBay just to test, they seem to be more available there.
Cheers
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If you getting one from the 'states, you can get them without SKIS, as it was an option out there. It would need to be from an automatic XJ 4.0 of the same model year. It might throw up some strange codes for some odd emissions related stuff as they have different equipment for some states, but you can just ignore those. The other option is to try one for a UK spec 1996 model, which is the last of the pre facelift with a 3 plug OBD2 PCM, which didn't have SKIS or VTSS enabled so should in theory plug and play.
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My replacement used PCM unit has arrived from the US and it does not have the SKIS enabled so I get that I need to disconnect the cable off steering column module for the SKIS system before I plug in the PCM.
Up to that point im ok is there anything else I need to know about before I plug this PCM in and power up?
What about the VTSS that Mike mentioned, I take it that is an alarm system but is that not part of the immobiliser (SKIS) module or have I got that wrong is there another module somewhere on the car for a 99 XJ and if so will that be an issue with the US sourced PCM
Having read up on the central locking I can’t see any problems and I think that will still work, as it seems to be independent of the SKIS
Any help or tips appreciated because if possible I would like run this new PCM permanently if I can, and not just confirm or dismiss the error codes that I have with the current PCM and TPS error codes.
bill