Hello all, as you have been reading lately, my jaguar XJ8 non-supercharged was having transmission issues, so I went ahead and bought one with 53,000 miles on it and replaced it. After replacing it, however, my mechanic noted that limp mode did not Go away, and that transmission fault Error continued to show on the dash display. After scanning the car with the OBD tool, we found three separate codes, ABS wheel speed, sensor fault, Pedal position sensor fault, and throttle data loss fault. After consulting with some of you, here, and my own research, we concluded that it would probably be best to replace the throttlebody and pedal position sensor. this worked momentarily, before the car went back to limp mode. It has now been almost 5 months since I took the car to my mechanic and he still hasn't been able to figure out what's wrong with it. He even hired two electricians to come to him and try to figure out what was going on, they couldn't figure it out. He blamed it on their inexperience. I have called him today and told him that I will be picking up the car. Before anyone tells me I should give up, no, I'm not. I have a different vehicle that I daily now, and the jaguar is simply a project car now. I have no rush to fix it or sell it. My question is, what do you gentlemen Think could possibly be the issue, an issue so problematic and complex that not even electrician and mechanic can figure it out? There's still quite the possibility that all of the issues may be caused by the ABS speed sensor. any help is appreciated, thanks, eric

 

Posting a COMPLETE DTC scan of ALL the modules might make diagnosing a little easier.
Seems to be some C codes and P codes that might point to something on the CAN bus?

WDS or IDS complete scan would look like this.

 

Job one: Find a new tech! Lots of them in Southern CA.

 

Just spoke with mechanic, can't get a full scan but he says the electrician mentioned the can bus line being faulty. No/poor connection from TB to ECU. I'm gonna need to take the car someplace else where they can properly diagnose the area of fault or voltage issue.

Also, none of the codes erased after swapping TB. I'm quite certain this mechanic messed something up while swapping the trans. The c and p codes weren't there before. Maybe somewhere near the J gate?

 

I just thought of something to check. Sounds like now the car is saying that it can't communicate with the TB at all. Did they attach the metal brackets and install the bolts on the bottom of the TB or did they just leave the whole assembly hanging from the plastic manifold? There's two little metal brackets that are directly above the top two bellhousing bolts. If they thought they needed to remove the TB for access, they may have removed those little brackets depending how they went about it. Did they get put back? They're small, hidden away, difficult to access and so could easily be overlooked during re-assembly. My guess is that without those brackets and the bolts cinched tight, the TB is not well grounded, or maybe not grounded at all. I can imagine the car's computer brain thinking to itself, "Hey, I can't complete a circuit to these critical things so I'm just going into limp mode." I borrowed a picture of an engine for sale off a famous online auction site and circled the brackets in red for reference.

 

Mechanic said he didn't remove the TB to remove the transmission, I'm assuming he did it the hard way. You're positive these brackets can for certain cause the issue? As for putting those back, who knows, I honestly doubt he did though, he doesn't seem like a meticulous man. He probably put them on a shelf and forgot about them. Either way, thank you so much for your reply, and will check that area once I get the car back.

 

The TB does not get/need any ground through its body. It gets ground through one of the wires and it is only for the Air Assist Valve. All wires related to the Throttle Motor, the PPS and the TPS go to the ECM.

 

Another vote for codes? Actual numbers?
We just can't help without real information and just repeating what somebody said is of no value?

What codes were present before you replaced the transmission?
Did the code/part number on the transmission match what was originally in the car?
Do you still have the original transmission?

Is your mechanic using SDD as motorcarman ask above?
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Finding a competent mechanic for these complicated cars is a daunting task. Finding one willing
and capable enough to chase down a communication problem without charging more than the car
is worth would be phenomenal! Our choices narrow to becoming more knowledgeable toward the
systems employed or replacing our beloved Jaguars with something different. The problem with
the latter is, of course, a whole new and unfamiliar territory of issues which may not be as well
supported as they are within this excellent forum.

 

Might be a shot in the dark but the wheel sensor may be the underlying issue. Might as well change the rear ones to see if it make a difference; or change them both. This site had a two pack for less than $20. Easy to swap and even easier if you remove the wheels.

Cheers!

 

I have posted all the codes on my previous threads, I can go pull them if you'd like. But all you need to know is before the transmission swap, I had incorrect ratio code, and that code only. After the swap, the incorrect ratio code disappeared, but then I got the aforementioned three other codes.

 

Swapping those now, will update after installation. Thanks!