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[ChrisS]

Yes, I now, it's got TPMS

Anyhoo, it seems to work fine, and has done since I got the truck.

Had LPG put on it almost 2 years ago now, removed the spare to make way for the tank - no problems.

...until today. Got in the thing to come to work and the EVIC said 'spare tire low pressure' which is a neat trick, given that the spare is in the back garden. If I step round the EVIC to the TPMS display it reports 4 good pressures on the 'active' wheels.

Confess, I have yet to go look in the garden store to see if the spare is indeed low.....

Anyone got any experience like that with these things?

[Cockney Boy]

my money is on a Sensor fault. best do a fault scan and tell us what code it comes back with. Or go get the spare and put it near the car and see if the fault goes away.

[Dutch]

http://www.birtydastards.com/frm/index.php?topic=21590.0

Not much help but a problems shared is ........ 

[ChrisS]

Thanks for the thoughts chaps.

I will do a scan, and also try putting some air in the tyre too - never know!

It's odd that it should pop up almost 2 years after removing the spare. It's been in the garden store all that time.  I'll certainly be impressed it is actually reading the tyre from that far away.......

Had another odd one the other day - MIL lit up, pulled the code and it was P2610 (IIRC). Looked it up and it was one of the more obscure and unhelpful ones so did a quick Google. Turns out it's my fault for fitting a coolant pre-heater. I've confused the poor PCM by having the water warm up before the engine starts. There is a software update, but I don't think I'll bother somehow - dread to think what they charge for those.

..and even odder...no MIL today, despite it being about -4 outside and the water being at about 80 before I started it.

Too damn clever for it's own good I think.

[demonicwillow]

So how is that any different from starting up after you driven somewhere, stopped then started up warm and driven off ?? tis a weird one that

[JamesH]

They really are way too clever and measure and adjust everything

[ChrisS]

So how is that any different from starting up after you driven somewhere, stopped then started up warm and driven off ?? tis a weird one that

I think it counts the time it's been sat not running for as well, and it's got a 'map' of how long it takes to cool down in given ambient conditions. I think I can persuade myself it's a smart-arse way to figure out if either the ambient temp sensor or the water temp sensor has gone tits up.

Thoroughly OTT I think.....   I can understand the need for the careful measurement of oil viscocity in the MDS engine - had it throw one of those codes when I got it since the trader had given it a quick & dirty service....with the wrong oil, but this water temp thing is just way overboard.

[JamesH]

The CRD is just as crazy, I could be gullible but have been told the glow plugs receive varying voltages from a controlling module during normal running if combustion isn't perfect so that emissions are correct, fuel economy maximised etc. Also, given the multiple ECUs and control modules for everything, one small electrical glitch can cause chaos.

[ChrisS]

I know nothing about diesels, so couldn't begin to say if that would make sense or not, but it's certainly plausible from the electronics point of view..and if it's possible, then Jeep probably programmed it.

Checked the tyre pressure in the spare at the weekend...and it was low.  Do find it hard to believe it would be able to ping the sensor from that far away though. Mind you, it was still complaining about it yesterday so perhaps I will have to put the wheel next to the car to shut it up.

I thought the wheel sensors were a bit like RFID tags - powered by the scanner. That being the case, then no way could it be reading the spare.  Anyone know for sure?

[JamesH]

Bluetooth?

[Jonny Jeep]

Tyre pressure sensors/transmitters are battery powered. When the battery fails the TP sensor has to be replaced. This is from the 02 FSM tyre pressures will vary on model/year...

TIRE PRESSURE MONITORING

DESCRIPTION

The EVIC will monitor the tire pressure signals from the five tire sensors and determine if any tire has gone below the low pressure threshold or raised above the high pressure threshold. Refer to the table below.

LOW TIRE PRESSURE THRESHOLDS
SYSTEM STATUS INDICATOR
TIRE PRESSURE
ON 179 kPa (26 PSI)
OFF 214 kPa (31 PSI)

HIGH TIRE PRESSURE THRESHOLDS
SYSTEM STATUS
INDICATOR
TIRE PRESSURE
ON 310 kPa (45 PSI)
OFF 276 kPa (40 PSI)

The Remote Tire Pressure Monitors (RTPM) are not internally serviceable. For a Sensor Failure or Low Battery fault, the RTPM must be replaced.

OPERATION

If equipped with the Tire Pressure Monitoring System, each of the vehicle’s five wheels will have a valve stem with a pressure sensor and radio transmitter built in. Signals from the tire pressure sensors are received and interpreted by the Electronic Vehicle Information Center (EVIC). A sensor in a mounted wheel will broadcast its detected pressure once per minute when the vehicle is moving faster than 40 km/h (25 mph). The spare tire sensor will broadcast once every hour. Each sensor’s broadcast is uniquely coded so that the EVIC can determine location. The individual tire pressures can be displayed graphically on the EVIC

DIAGNOSIS AND TESTING - TIRE PRESSURE MONITORING SYSTEM

All Tire Pressure Monitoring System Faults are specific to one location. If a BATTERY LOW or SENSOR FAILURE fault is detected, the location will be displayed. The appropriate sensor/transmitter can then be replaced. If a single sensor/transmitter cannot be detected by the EVIC, replace that sensor transmitter.

[ChrisS]

Thank you sir - that all makes sense.  Suspect I'll need to carry the spare around in the back for a bit to shut it up then.....

Unless there is two-way comms going on, then I suspect the sensor has some kind of wee switch that triggers the once per minute mode once it gets up to speed. I'd guess they all ping at once per hour at rest.

Pressure in the spare was down to about 25 so bang on the trigger threshold.

[ChrisS]

Well, got round to putting the spare in the back over the holiday...and sorted.

I managed to find out a bit more info on the system installed on the later cars but apart from a few detail changes, it's as JJ posted.

FWIW, they use the 413MHz band (same as the remote) to transmit in this country and are supposed to have a 10 year battery life.

Thanks all - 'problem' solved. Came down to RTFM really.....

[Plank]

By christ these cars are clever. Glad mines a 1998 so it doesn't have the latest over complicated shit