Update:

I did a road trip with the WJDiag Pro app connected, cleared all codes before the ride and monitored some live values. To my surprise, the transmission code did not occur during the trip but the 3 other engine codes did AND the jolt that was being felt, directly relates to the fuel pressure code! The pressure reading jumped from a correct pressure reading to 0, causing the MIL to light up. The transmission is no longer suspect and none of the sensors are neither, this now shifted to an electrical issue.

After more research, it appears that all these sensors potentially share a common wire/harness and that it's a known issue that these can get damaged and short out. My next move will be to completely rewire the following sensors:

- intake air temp
- cam position
- fuel rail pressure
- t-case switch (there's a Jeep bulletin regarding this wire, causing a different code P0836 that I don't have, but I'm replacing the wiring anyway)

I will also be checking the transmission connector for oil, because that appears to be a known issue as well. There's even an adapter available that stops oil wicking into the wiring: https://jeepswj.com/tips/ (point 4)

Will keep you posted...

Hi gang!

Been a minute since I posted something on the forum. After my last posts my father-in-law was able to enjoy his Jeep until recently it started acting up again. The phenomenon is the following: while cruising, he feels a sudden short jolt (I'm guessing gearbox) after which the check engine light comes on. When he turns off the car and turns it on again, the check engine light is gone. He's a really relaxed driver (read: sloooow), so he unfortunately doesn't know/feel the difference between a car stuck in limp mode or not. I haven't been able to reproduce the issue driving it myself yet. It has the following codes (some likely unrelated).

Engine Control Module:
P0110 Intake Air Temperature Sensor Circuit (it's in the mass airflow sensor I read, which I already replaced, so I guess it's not the sensor, haven't read the live data yet with WJDiag Pro)
P0702 Transmission Control (generic code for issues with the transmission?)
P0190 Fuel Pressure Sensor Circuit Malfunction (haven't replaced the sensor yet, also haven't read the live data yet with WJDiag Pro)
P0340 CMP Position Sensor Circuit (replaced the sensor already, didn't fix it)

Transmission Control Module:
P240D ID 44 Engine T-Case Switch Message

I tried to replace the t-case 5-position sensor; bought a new, but apparently faulty, unit from a German jeep shop (couldn't find it anywhere else at the time), but it immediately threw a P2502, transmission slipping. When I measured the resistance at the ECM (between pins 29-21) I noticed that both 4Lo and 4AllTime read 60 Ohm, neutral 200 Ohm. I then checked the old sensor and it read roughly 60/200/400/700/1200 Ohm according to spec, so I put it back and the P2502 disappeared. So it's NOT the sensor (unless it fails when hot or so) and NOT the wiring (unless it rubbed through somewhere and shorts while driving).

I also found a shifter-PCB that could be the cause of the P0702, but not sure if that causes this jolt? Either way at >350EUR for this PCB, I'm done firing the parts cannon at this thing, it's getting ridiculous.

I read the codes both when the MIL was illuminated and when it was not, the codes all came back exactly the same, so the code triggering the MIL to turn on disappears again? I would guess that it would get saved?

Could use some help figuring out this issue.
Oh, and if you have tips on the other codes, always welcome as well!

Cheers
Nic

Hi thanks for the info, i have always disconnected both battery leads but after reading on some of the American forums about frying electronic components i started to worry, I really don't fancy playing around with the pcm connections and possibly causing more problems, they have never been pulled apart since the day it was built.
Just had a bad day trying to fit a replacement transfer case linkage (from Amazon) but it will not fit i suspect because its a diesel and the gearboxes must sit further forward, so the adjustable linkage is far too long, more wasted money, so will have to reconditioned the original setup and live with it.
Thanks for the reply.
Cheers Ian

I've welded on my TJ without disconnecting the battery or PCM. Done the same on vehicles at work too. I'm not sure it matters much, if at all, as long as you have a good clean ground close to the place being welded.

Anybody have any advice regarding welding on 1999 diesel xj cherokees, ive just had my mot done and been given an advisory for some welding that needs doing to the chassis rail just forward of the drivers side rear Spring mounting.
I know to disconnect both battery leads but have read some horror stories on US forums that you can fry the PCM unless thats disconnected as well, not sure how to disconnect them and dont really want to disturb them if i dont need to, anybody with any experiences or advice I would like to here your comments, i dont want to totally fry my Jeeps electronics.

List of the chosen for cheapfest 2025

It's a sad day when the minority spoil it for the many.

I believe something similar happened at Seven Sisters / Walter's, resulting in clubs not being allowed to book the site.

Just so people who aren't on FB are aware.

Hi guys, my old TJ 97 has been in my local garage for 3 months after what seemed like a radiator issue. The garage is now saying one of the core plugs in the cylinder head is shot (and can't be re-bored), so I need to replace the cylinder head. I'm not happy it's taken 3 months for them to diagnose the problem, so can anyone recommend a Jeep specialist in Essex or Hertfordshire  (preferably near Waltham Abbey/Harlow). I'm looking to sell my TJ - which has been so much fun for the last 10 years - and just need to figure out cost implications......do I repalce the cylinder head then sell, or just sell it as-is to a Jeep fan who is handy with a spanner?

Hi all

Have a little question, I was putting in a new head gasket, and I noticed that the fuel injector with the sensor wire was actually in cylinder number 2 and not cylinder number 1, it must've been like that for years, as I've had the jeep for 8 years and I've never moved it. My question is, does this cause any issues and should I move it?