Hi All, long time since I was last here, actually forgot that I had a log-in and was reading through posts when I stumbled across my own profile.... what a moron!

That aside, my car has been laid up for the last few months with a very annoying problem.

The car starts fine and runs fine, it was my daily driver before the registration expired and I couldn't get it passed smog.

The CEL was on, and using both of my readers, I cannot communicate with the ECU. I took it to a local shop and they can't talk to the ECU either.

I replaced the ECU with a junkyard part with EXACTLY the same part number (what are the odds of that...?) and the CEL was no longer on, so yay! Except I still can't communicate with the ECU...

Does anyone have any suggestions? Wiring? something else?

I'm at a loss and fighting myself over whether to spend $$$$ on *maybe* getting it fixed. I love the car, it's in decent shape and it has only 118k miles. But there has to come a point when one decides it's time to let it go....

 

I don't have my manual right now, but I'm fairly sure there is a fuse for the obd plug.

 

John,

The Datal Link Connector (OBDII port) receives power on the Brown/Red wire from 5A Fuse #6 in the trunk fuse box.

It might also be worth cleaning the Logic Ground Stud, which is inside the right rear fender behind the carpeted trim panel. The wire or wires connected to it are Black with Pink tracer lines. Clean all the other grounds in that area while you're at it.

You can download the 1996 X300 Electrical Guide here:

http://www.jagrepair.com/images/Auto.../jagxj1996.pdf


The wiring for the DLC is shown in figure 21.1 in the guide.

Please keep us informed.

Cheers,

Don

 

Thanks guys, I contacted a local Jag shop and the guy there mentioned the possibility of no power to the OBD port.

I just went and checked all fuses in the trunk, then I found the fuse map on the fuse box lid under the hood. Can't see any reference to OBD, but I'm half-assuming that "JDS" is Jaguar Diagnostic System. That fuse is labeled as 10A, but it's not blown. None of them are...

I checked the ground contacts while I was there, everything is extremely clean, so I'm at a loss again...

Any other ideas?

 

Sounds like a time for a session with the electrical diagram and a digital meter. Test the pins for 12 volts at the socket. Disconnect the battery and "ohm out" each circuit from the socket to the ecu. Stand on your head with a good flashlight and examine the socket pins.

The fact that both ecus display the same behavior means it is either wiring or you have experienced some serious bad luck!

 

Thanks Ross,

I've booked the car in for a diagnostic at the local Jag shop, hopefully they can give me good news. I'll happily swing a wrench on any major mechanical repairs, but I hate troubleshooting electrical problems, so rather than give myself any more ****-ache, I'll let them deal with it.

Once I've got it smogged and road-legal again I have some other issues to fix (AC, steering, interior, paint blah blah blah), I'm sure there'll be something else to ask for help on.

Thanks again.

 

Do you have any non original electrical equipment installed? The reason I ask is that I had a similar problem with an Audi recently. Turned out the non factory stereo had been bodged into the CANBUS wiring system, and whilst it worked, it was blocking the signal path to the ECU. Disconnected it, and all diagnostics restored.

 

Interesting.... The only non-original equipment in the car is the stereo. I had an aftermarket unit "professionally" installed for the MP3 connection, but that was 5 years ago, and it's passed a California smog test twice since then. The CEL just came on last year, right before the smog test due, so I never gave it a second thought. Seems unlikely it would wait 4 years before presenting a problem, but what do I know? It originally came on after one fill-up at a "discount" gas station that I suspect was regular gasoline instead of premium, and I was assuming it would right itself after the correct fuel had cycled through. That was countless-tanks-of-gas ago...

With that said... if the CEL isn't on at the time of a smog test, they have no cause to try to connect to the ECU, so I suppose the stereo wiring could have been the problem the entire time. Has to be worth a look.

I'll try it today after work, but I have it booked in for a diagnostic on Friday anyway. I feel a solution is near.

Still, at least I don't have to deal with the same problems I used to in Scotland. Although strict in California, smog checks are only required every 2 years. Rust isn't an issue, nor is weather when repairs are needed, and we never have to endure the agony of an MoT. It's like waiting for your first-born child to be born. Every. F'n. Year....
I hear the "beloved" annual inspection is even more oppressive these days!

Cheers mate!

 

Three weeks in the shop and my Check Engine Light issue is fixed.

As it turned out, there was a short in a connector (a bent pin) somewhere in the circuitry of the Check Engine Light itself. There was no issue with the ECU after all, the fact that it wasn't giving me any codes is simply because there weren't any! I had reset whatever codes were stored but since the CEL never went off I assumed (as did the other shops that had looked at it) that the ECU was bad.

In the meantime while it was laid up since the tags expired, I replaced the harmonic balancer because it was completely shot, and I believe that was the original cause of the CEL when it first started to go bad (timing was being upset).

So now I have to drive 100-150 miles with my fingers crossed to reset the ECU readiness for smog and hope that fn CEL stays off.

Three weeks in the shop and they only charged me 3 hours, now that I like!

 

John,
Greetings from the peoples republic of Scotland!
No, the annual MoT is not becoming any less oppressive, with airbag warning lights and split balljoint gaiters recently being added to the list of automatic fail items. On a more positive note, it is now possible to see a vehicles MoT history online, including any "advisories" (items which the owner should be aware of, but which do not justify failure at that point in time), which can be very helpful when buying a secondhand vehicle.
I'm glad to hear your check engine light issue is fixed. I have come across a couple of issues where connector pins have broken or lost contact. In each case, there was a multipoint connector with 12+ wires going into it, and a sharp bend in the cable run just before the plug, which was in effect putting pressure on the connectors. The passage of time seemed to do the rest.
Anyway good result with you CEL.
PS Rust isn't such a big issue here nowadays, and thanks to Ford, the X300s are dramatically better than everything Jaguar that went before!

 

"People's Replublic of Scotland"... I like that, it has an independent ring to it... one day...

 

Looks like I am reopening an old thread, as I am hoping to clarify a point to help in my diagnostics!

I have a similar issue to the original post, my CEL is on and I have no connectivity to the ECU. The original has been swapped out and no data is able to be read from either ECU in the running Jag. The swapped ECU was giving fuel trims and data in its original car. Fuse is good, next check is the 12v, however my meter crapped out so am picking one up this week.

The point I wish to clarify is 'OHM out to the ECU'. Is this by going from each diagnostic pin to the ECU itself, or from the Diagnostic pin to the ECU pin on the plug?

Thanks in advance for the help, I can start a new thread if preferred too.

 

Lets pick up on your new example

The ECU is powered from a First Power source and a Second Power source once the first is " on "

This from the right engine bay fuse box small relay # 9 in the corner of the fuse box ( 1st ) and fuse # 12 ( blue wire path in the pic ) and the large # 5 ECU Controlled relay ( 2nd ) and fuse # 11 right engine bay fuse box ( red wire path in the pic , and fuse # 6 as the relay control power always " sitting on the relays pulling / clamping coils ) that the relay is controlled by the ECU ( purple wire path in the pic ) and brings power back into the ECU

You have relay swapping options from others on your X300

You will see this in the following 3 pics coming

Your Canadian 4.0 model will be the same as this supercharged pic but you only have 2 / O2 sensors as mounted rear and the fwd positions un occupied ( only serves that the Cats effeientcy up to par as CEL code 420 and 430 abouts when below par )

There is a fuse # 10 small 5 amp Right heelboard ( rear seat by heels panel ) fuse box that powers both your Fuel pump relay " control " and a power pin in the OBD2 port ( someone did find a bent pin in his OBD2 port ) . This requires that relay in the heelboard fuse box to remain closed to power fuse # 10 ( to test remove relay with ignition key in run and remove the relay , that relay should click back to open on removal )

Ask questions and We'll be on statiion and operationaly ready