Hi all!
A weird but seemingly known issue popped up on my 1996 XK8 Coupe:
The issue happens almost only when turning on the ignition (not starting the car) on a cold engine (even if hot outside).
After letting the car idling for 1 minute, cutting the ignition, and putting it on the ignition key position, the gearbox fault disappears.
It rarely happens when driving, it is possible but very unlikely. Once the engine is hot, the fault is very unlikely to reappear when turning the key to ignition.
I charged the battery and since the fault appears before cranking, I think the voltage is not the issue here.
I have tried moving and jiggling the J-Gate but it seems to work perfectly and I cannot reproduce the issue once the car is running with the fault cleared.

Could it be a bad connector inside the rotary switch, which actually connects when the temperature rises?
I have seen several DIY possible repairs for the switch, or people that can refurbish them, but I would like to be sure that the problem comes from it, and I don't know how to check that properly...

 

How old is the battery?

Richard

 

From the documentation DTC list:



...but definitely check the battery first.

 

There are two ways to ensure the DTC is not triggered.
1. Never use the 4,3,2 side of the 'J' gate.
2. Make sure the D4 switch and plastic cam plate are mounted correctly and not broken.

 

The DTC is already triggered when I turn the key to position 2 when the engine is cold, I do not even need to use the J-Gate's 2/3/4/N/R/D positions.
Jiggling the J-Gate or moving the J-Gate to any position, when the fault is cleared, does not make it pop up again.

The battery is two years old, it is a Varta Silver Dynamic 830A, 85 Ah. I have had a moment when it was discharged a bit and triggered the known ABS fault, but since it it charged, no issues whatsoever. This issue seems to come from a metal connector inside the transmission rotary switch that, when heated up, clears the fault and makes the connection.
Although I am not sure and I wonder what procedure I could follow to confirm or exclude the rotary switch being the culprit.

 

The fault is more likely to be in the D4 switch but the rotary switch can be faulty.
I have not found a faulty rotary switch unless it was physically damaged but..........
The rotary switch is easy to replace. it is on the side of the gearbox and does not need adjustment, it has a locating pin and two small bolts.
A used one can be had from a normally aspirated sedan (X308) or X100.

Possible causes
Selector cable adjustment / installation incorrect
D – 4 switch dislocated
D – 4 switch to TCM circuit open circuit or short circuit to ground
D – 4 switch failure
Rotary switch to TCM circuit open circuit or short circuit to ground
Rotary switch failure

 

Thank you for the info!
How can I pinpoint the cause between these 5 different possible failures?

 

I have checked, and actually, before turning the key to the ignition position, if I jiggle the shift lever when it is locked in the Park position, it can clear the fault. So yeah I will inspect the D-4 switch first indeed.