Long story long here.....
Am working on a 2006 XJ8 that is misbehaving as follows.
When the car is driven in a heavy rain, the CAN network corrupts and ECM loses communication with the CAN modules connected to it. This has happened over the last 3 months at the most inopportune times and in all instances has resulted in having the vehicle towed. After sitting for an hour or 2 the car starts fine and runs with no issues.
When it happened in March of this year, it was being driven at highway speeds under wet and slushy conditions. Codes that were stored included:

U0073 - Control module communication bus off
U0164 - lost comms with hvac module
U0103 - lost comms with gear shift
U0132 - lost comms with ride level control module
U0128 - lost comms with park brake module - this was disconnected during a brake job years ago so this one makes sense.
U0121 - lost comms with ABS control module
U0155 - lost comms with instrument cluster
U0101 - lost comms with TCM
U0167 - lost comms with vehicle immobilizer
P2105 - throttle actuator control system - forced engine shutdown
P1797 - CAN TCM to ECM malfunction
P061A - int. control module torque performance
U0415 - invalid data received from ABS control module
P0504 - brake switch a/b correlation
P0500 - VSS cct malfunction.

At this point the 4 year old battery was load tested and it did not perform to spec, so it was replaced.

May this year - driving in a heavy rain the instruments lit up like a christmas tree and car began to drive/shift erratically. Pulled over shut it off. Turned key - no crank no start. Electrical appeared to function correctly meaning lights and wipers would work. When the tow came, the car would not start or shift into neutral. Same issue as in March.
Codes from May episode as follows:
U0128 - lost comm with park brake (still disconnected so may be a red herring)
P1797 - CAN TCM to ECM malfunction
U0300 - internal s/w incompatibility
U0155 - lost comms with instrument cluster
U0402 - invalid data from TCM
U0100 - lost comms with ECM
U0001 - high speed CAN bus
P1799 - CAN TCM/ABS cct malfunction
P1774 - CAN timeout gearshift

So my gut is telling me the CAN high and low are getting wet somewhere and shorting out causing widespread network issues.

This weekend I checked all module connectors that are physically outside of the cabin of the car. All appear to be ok - no evidence of water intrusion or corrosion. I even sprayed garden hose water at connectors on:

ECM, ABS, DSC, TCM harness on transmission plus 3 harness connections found under the car near the driveshaft rear axles - could not replicate the issue
Also tried to simulate water road spray by hosing the car down underneath and directly onto the front end - grill/lower grill areas. - no issues

It rained heavily (including hail) so left the car outside for a good wetting - ran fine.
Drove it through the puddles - hitting deep water - ran fine.
Other points to note:
I have checked the CAN network at various locations and get 60 ohms plus or minus 1.
Deep checks in the passenger cabin reveal no evidence of water intrusion anywhere. All is dry inside the cabin.

Any thoughts/suggestions would be appreciated.
Really don't want to declare this as a fairweather car only.
Thanks

 

Ted,

This is a very interesting thread. There have been quite a few CAN bus communication problems cropping up here lately. My particular version gives similar CAN errors but not just when it's wet -- including your same P1774, P1799 and P1797. My problems have only manifested in gearbox malfunctions and intermittient failure of the cruise control buttons on the steering wheel so far. I have been systematically checking all the related connectors and grounds but this is a big job! There are 27 grounds alone. I fear that a bad connector or a weak ground anywhere in the system could cause all kinds of spurious symptoms and codes. I have checked the ECM connector, the TCM connector, the ABS connector, and all the under hood grounds. Right now I have the interior apart to go after everything I can find under the dash and the console, including the J-Gate connector.

Good luck and keep us posted.

Jeff