I finally got JTIS by connecting to my dad's computer. I cannot find diagnostic steps for P1638. I have no problem checking 2 wires between ECM and Instrument cluster (broken or shorted to bat+/ground/each other). If wires are OK(already checked them), it leaves me 2 choices: bad cluster or bad ECM.
If I can find diagnostic steps, I'll know which one.
Are there diagnostic steps in JTIS? Where are they? If they are not there, which manual do I need?
Thanks.
Attached picture is from DTC chapter of JTIS

 

You can't just connect wires as it's CAN. You must follow the CAN design requirements. (That said, it MIGHT work but you'll be misdiagnosing if it doesn't and good luck figuring which rathole you've gone down.)

Don't know about P1638 other than what the codes PDF / JTIS says.

If you have someone competent, maybe a jag indy, probably best to use them.

 

Diagnosing Jeep was pretty easy:
Manual said, voltage of CAN system should be 1.5-3v
If voltage is different, that means there is a problem. In my Jeep door window switch went bad and increased voltage to 7V. As soon as I disconnected door switch, everything went back to normal.
I am pretty sure this approach would be OK for a Jaguar:
check voltage, disconnect instrument cluster and check voltage again.
I talked to a local repair shop owner (very smart guy, but never repairs Jags. Is that one more sign to be a smart guy?). He said, he repaired about 10 cars with CAN problems, it was always some computer, going bad, never a wire or connector.

 

Sounds like you did not read up on CAN so anyone who knows it will be better.

 

run the ids program (it should show you a lot more information) and check it there. and read from page 2709 in that manual I sent you.

 

That is an extremely rare code and I am not sure the CAN bus is the problem?

I think what the JTIS is saying is swap one or both to see what happens. This is written for a factory tech so they will have access to things that we don't.

But I would start with simple stuff.
Have you cleared the code and did it come back?
How old is the battery? What's the voltage resting and running?
Check connections for corrosion and tightness.
Maybe find the relay for the ECM and swap it with another one. Most of the relays are the same.

Any work done lately?



PS: Kind of hate to post this because it's for an earlier car with the 4.0L V-8. But the TSB states you can get this code if the battery is connected when the ignition switch is in the run position.
Any chance that happened?


Was everything OK before this code?

Then if nothing turns up start looking at a new instrument cluster or other complex/expensive solutions.
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