I connected the ODBII Scanner and the Wifi/iPhone combo I had tried on this car to our X300 and they were all able to communicate with the ECM, so it appears they all have the proper ODBII protocols and no issues communicating with a good ECU.

I had to order the TS30 five point security bit to inspect the ECM connector because I couldn't source it locally. Got it today and pulled the ECM. There are no signs of corrosion on the unit or at the connector. There are no signs of water or prior water incursion in the area on the unit. Used contact cleaner on both the ECM and connector plug, and let it dry for several hours.

Checked the Ground Points G26 and G30 for corrosion. Though I didn't see any visible corrosion I used contact cleaner and a brass brush to clean everything up.

Same issues after reconnection.

So next I'll see if I can figure out what pins in the Data Link Connector coincide with the pins in the ECM connector and check for resistance. I'm feeling a bit stupid because I haven't been able to figure it out from looking at the Electrical Guide or the Electrical portion of the workshop manual so far.

Since this is really the first time I've ever had to work on something outside of routine upkeep, I decided this would be a good time to invest in a cloned dealer tool. After reading the threads on that (sigh... my brain hurts!) I ordered the British Diagnostics kit on eBay, which should be here shortly.

I have a couple of questions that I hope someone with the correct expertise can answer:

1) How can I test or specifically determine if the ECM itself is at fault?

2) If I purchase a known good used ECM from the proper VIN range, can it be plugged in to determine if the wiring and network is working without causing a problem?

3) Can the used ECM be programmed or matched to my car using the SDD software? (I have access to one that would be cheaper than sending mine out for rebuild or test)

On top of this, the high pressure power steering hose on the XJS decided this was the time to give out (worst job ever trying to replace it). Being short on cars this time of year... well let's just say the wife and daughters are losing in faith in ability to "fix anything"...

I'd really appreciate some of you who know this stuff better than I do giving me some inspiration or answers.

 

Check my link first and try that before ECU change.

 

Yeah i'd be checking fuses now.

Have a look in the owners manual it lists out all the fuses, there are some which could explain the car being dead like this, for example;

There are fuses for the diagnostic connector
There are fuses for the ECU, as well as major electronic modules

And so on...

In answer to your questions;

1. A replacement ECU can be fitted and re-programmed to your car, provided that the vehicle is able to talk to the IDS/SDD diagnostic system, which it probably can't do at the moment.
2. If you plug in an ECU which is not coded to your vehicle and try to start the car, the security system will be activated and the vehicle will be immobilised
3. See answer #1

Check fuses relevant to the problem you have, or if you have time check them all...

 

I should have mentioned that I checked every fuse that looked like it might be related, but it might not be a bad idea to just check every fuse.

So, to confirm and so I don't do something stupid -- a used replacement ECU can be plugged in to test communication and wiring, but DO NOT start the car or it will be immobilized. Correct?

Thanks

 

I read through your linked thread, but it seems like you could communicate with your ECM and pull a trouble code. Did I read that correctly?

At this point, I can't even pull the DTCs.

 

Good news -- The car started

Bad news -- Not sure why it started

OK, now there is some interesting new information.

I had put the ECM back in, re-checked all the fuses, re-cleaned some groundpoints, etc. and I checked to see if there was any change. There was no change, I turned off the ignition, thought I heard something perhaps a relay click from the engine bay, tried the key again, but this time instead of the display starting with "Gearbox Fault" it started with "Bonnet Open" and "Engage Parking Brake"... so I turned the key and it fired right up.

After the car started, and while it was running I plugged the ODBii Wifi interface in, and this time had no issues connecting with ECM and communicating with car. Most interesting there were no DTCs other than P1000 pending code. I let the car run quite awhile, drove it around a bit, but no fault messages appeared on the display or DTCs recorded.

Started a second time... but not a third, and it has returned to it's dead state with same error messages on the display.

Hearing that noise prior to it returning to a working state I would hope is an important clue. I tried pulling ever relay I could find, inspecting the contacts, and reseating them, but did nothing.

Would a stuck relay cause current draw to confuse the system?

What else could it be?

Really need help on this. Thanks

 

Just curious, but where is the problematic front grounding point? It just crossed my mind that it may be the source of my ACC failure.

 

Just for my understanding

So now it's back in the dead state again, you can't communicate via the OBD port?

This is a weird one...

 

The connection is weak in the module inside the car.

The one underneath the radio setup, and the one just right underneath the parking brake lever thing but mine is the unit under the radio setup. Center console have to be pull to access that module which I forgot what that module it is call.

 

Exactly. Plus when it started and could communicate there were no DTC's and everything was just peachy.

 

There are three grounding points on either side of the radiator, on a LHD drive car there are two on the passenger side and one is on the driver side. These are the ones most exposed to the elements. Additionally, the two in the trunk that the battery negative terminal is attached are also reported as problematic over time.

Word of caution. The threads and nuts are aluminum so be careful with the torque.

 

So far it sounds like a bad connection/relay/fuse but not a suspect module.

 

[QUOTE=Mac Allan;1123258]Good news -- The car started

Bad news -- Not sure why it started


Would a stuck relay cause current draw to confuse the system?


The short answer is YES, a stuck relay could drain a battery very easily as well as burn itself or some related circuit out.

I've never bothered to look or ask but do the Jags have any inline fuses, especially in the ignition circuit, or perhaps some sort of a circuit breaker anywhere?

Your series of fixes, adjustments, and cleaning seems to have caused a situation where enough juice was able to get through before what every is causing the resistance to stop the flow of electricity to once again build up.


I'll have to review your steps again to see if I missed a hint.

 

I measured the voltage at the battery - 12.71

Then measured the voltage at the cigar lighter -

Key position I - 12.64
Key position II - 12.53

Key position II after 1 min - 12.44

Cycled between 12.42 to 12.44 over the next several minutes.


It occurred to me that on the prior occasions I got the car to start, it was after "doing something" cleaning contacts, jacking up the front to inspect the shift cable, etc. IOW, the state of the car had changed in some manner between it working and not working -- except in this last instance.

The car was in it's failed state, key turned to position II, no change.

I turned it to position I, then back to position II, hear something, no fault messages, and vroom it starts and ODB2 communication resumes.

Therefore something changed between the first attempt and the second, that was only caused by turning the key from II to I to II. So I think one of the following might be happening:

1. Something is NOT getting turned "on" that needs to be on for the car to start, but also to facilitate communication from the DLC to ECM.

2. Something is getting powered up, and that power is putting it into a state that interferes with the ECM.

 

Suspect relays or even power/ground somewhere.

 

Hi all, I've been studying the various schematics looking for something I haven't yet checked, and it looks like ground/earth point G32 (LHD) might be a potential culprit.

It is described as being behind the instrument cluster. I can't see it so far from beneath. Does anyone know how to access G32?

 

Found G32. Unfortunately, it's not the cause of the issue.

 

Here's a potentially useful link if you can find your starter relay.


https://www.jaguarforums.com/forum/x...-relay-133272/

 

Got my IDS/SDD software installed and connected to car.

Here are two screenshots:








Comments?

 

I should note that I took those screenshots after disconnecting from the car and going back to the session, so you can ignore the red battery icon.