Hi Folks, another question for you. I have been having some major problems with my Jag. It has been deciding not to start for days at a time, the doors are locking and unlocking and registering as open when closed. I feel like my baby has lost her mind. =(. So we are convinced this is a computer problem. I was amazed to find used ECMs for this make and model are surprisingly inexpensive, but if the ECM does not come with the compatible Key, how do I program it to my mine?

 

I'm not sure about swapping a used ECM - VIN is written to it once programmed. Anything that needs to be programmed, you would need someone with SDD, or the dealer.


Before you proceed with swapping ECM's, what is the issue or issues you're having?

 

Thanks for replying. Where do I begin. It randomly won't start w/dash reading restricted performance, the gate wont open, sometimes it insists the rear driver door is open when it's closed. It unlocks and locks every time I try to start it when it's behaving this way. It also reads empty when the tank is at least half full randomly before and during it's episodes. Last week it went to restricted performance while I was pulling into a busy street, and just died right there. It wouldn't start for 30 or so minutes then just fired up like nothing was the matter. One time it wouldn't start for over a week I had to have it towed from a friends, then randomly started a few days later.

 

Have you tested the battery?
Multiple threads in here about the issues encountered with a failing battery.

Also you need to scan the fault codes which may well help in identifying the issue(s).

Last resort would be replacing the ECU.

If necessary get it reprogrammed/re-flashed. But start with the easy things first.

 

There are no fault codes. How does one get it reflashed? I'm not sure about battery, but it has a lot of cranking power.

 

I thought I replied to this..already but in case it didn't go through, Not sure about battery, but cranks with a lot of power for a long time when it wont start. Lights and bells all come on. There are no fault codes, no check engine light on. =/. Every now and then it will read to check fuel filler cap.

 

A long shot but you could try a hard reset by disconnecting the battery leads and touching them together for about 10 seconds

I suggest getting a proper scan thru the ODBII port for error codes before doing anything else.

IF there is an issue with the ECU and it is not damaged then someone with the correct software system can reprogram it.

A dealer obviously can do this but will charge a lot whereas an independent Jaguar mechanic probably a lot less.

 

Thank you Jackra, what is touching the leads together doing? Is it discharging capacitors or getting rid of static?

 

Discharging capacitors some of which maintain "soft" chips logic. Probably will not help your situation but worth a shot.

 

ECM is the very last suspect.

Battery is #1 suspect.

Wiring etc are next.

Do not reflash or replace the ECM until you are SURE you have eliminated every other possibility AND you know about anti-theft mode. Get the free workshop manual - BTW it's in the S-Type forum where this ought to be.

 

And one for you. Why post in Other Jaguar Models / Concepts / Replicas forum?

I've moved it to S-Type forum.

Graham

 

I think there's even more to it. Somewhere in my stack of documents, it says an ECM cannot be transferred from one vehicle to another. Once the VIN is set, it cannot be overwritten. This means if you tried swapping in a used ECM, it cannot be made to work with the rest of the car, even with dealer-level programming. The only way to replace an ECM is with a new "clean" one that has never been assigned to any vehicle.

That would explain why the used ones are so cheap. They won't work in another vehicle. I can search for this info if interested.

 

I did a lot of research on this as I was considering replacing mine. When I posted a question on this topic a week ago or so I did not get any definitive response other than how to re-flash my existing one.

Where I was able to see posts on this topic none were conclusive one way or another.

The worst scenario that I could see happening would be getting locked out when trying to reprogram a used ECU.

I presume that would be overcome by putting back the original but I am not even sure of that .

The ECU is "non volatile" memory but has to be programmable in the first instance so why could you not reprogram/re-flash as if it were the 1st time?

 

It's not a one size fits all answer as there are several different PCMs depending on year, engine, etc and the rules vary.

As it's almost never the PCM go hunting elsewhere for problems until you have nowhere else to go.

In the extraordinarily rare situation where it really is the PCM you can then get into whether it can be reflashed and if not then how many modules you'll need to buy to avoid anti-theft. (Expect pain.)

If you're thinking along the lines of "do they lose their programming" it appears not. Or "do parts inside blow readily", definitely not. As I put, PCM is the last suspect.

 

I must have missed that thread. I'd have chimed in if I had seen it. Here's the info, straight from Jaguar, via Gus:


http://www.jagrepair.com/images/Trai...es/870B_SG.pdf


Read pages 1-8 through 1-10. It describes how once the VIN is written into memory, it cannot be overwritten.

The note on page 1-10 is even clearer:

"Once a PCM is configured to a vehicle, it cannot be reconfigured to another vehicle."

The same page also mentions: "The new PCM must be configured to the instrument pack as part of the security system set-up. If this is not carried out, the engine will not start."









Oh, sorry, I missed this part until just now. Somewhere, in a different document, it said the PCM sends out certain internal configuration data to be stored as a backup in other modules. If you install a different PCM, it also tries to send out its own data. The way I read it, if you then try to reinstall the original PCM, you now have a big conflict. At the very minimum, you would need dealer-level programming to be able to reuse the original PCM.

Dang, I wish I could find it again but I'm having a brain fart. But no matter, the upshot was don't swap PCMs. Install a new one if needed, but don't swap from vehicle to vehicle.

Back to the OP, I'm with the JagV8. I highly doubt the PCM is at fault. Have you checked for water in the spare tire compartment? There are lots of electronics back there that could have been affected.

 

So... how about we get back to the OP's problems...

They DO NOT sound like a PCM fault.

They sound like bad power, bad battery, bad loom, water/damp, etc, particularly as the problems described are in many cases NOT the responsibility of the PCM but instead belong to other module(s).

Proper diagnosis is needed.

I note the part "So we are convinced this is a computer problem" - who is WE? Whoever it is must have a poor grasp of the car's electrical and computer systems! Please go elsewhere.

 

Yes!! My Jag had a lot of water in the spare tire compartment! What kind of problems exactly does that cause. Why was there water and how do I undo the damage done? A new problem it's giving me is the tail lights are randomly going on and off at will. Not the brake lights or even Hazards work when it does that. Which I know is extremely dangerous, but my Dad just had a Massive Stroke and I have to get to the Hospital where is in the ICU, 35 miles away. I have to get that fixed right away. If I brake down I can live with that. I don't want to be risking lives including my own though, and that makes the tail light issue priority number one.

 

@Jagv8 - My husband is a long time Mechanic, he really does know his way around a vehicle. I have seen him work many miracles many times for many people. But this one has him stumped it is fair to say this our first ever Jag. But when it broke down in front of a friends house. He tried all sorts of different things, assuming it was the fuel pump but then he tried bypassing the fuel pump with another one to see if it would start and still nothing. He has scanned it for codes. He charged and tested battery, checked relays, circuits, nothing gave any clues as to what was the matter. We had to have it towed home then he just decides to give it a shot and it turned on as if it never had an issue. Since then he has spent hours outside getting to the bottom of it, he even tried the hard reset Jackra recommended, He can't think of any more possibilities, which is why I'm here. You know it's bad when my husband is willing to check his pride at the door and turn to someone- anyone for help. And believe me I would MUCH rather it be anything other than the computer, because if what you all are saying is true and it's a matter of buying a new one and going to a dealer then it might mean parking her. =( p.s. Where can I find the free workshop manual?

 

Bypassing like that is not going to work. The car is a networked computerised system.

It would be wiser to get the free workshop manual and other stuff and study! Not only is it explained but also there are details of how to go about testing just about everything.

There are plenty of threads about water like that with what to do to find & fix it so go reading

 

We may be running into a nomenclature problem, especially after the thread morphed a bit in the middle. I just realized we've probably been talking about some very different computer modules. In this thread, we've mentioned the ECU, ECM, PCM, and who knows what else. I know I've added to the confusion. Sorry about that.

The module that cannot be swapped is the Powertrain Control Module (PCM).

Your symptoms seem more likely to be the Rear Electronic Control Module (RECM). I don't what programming, if any, is required. For all I know, it may be plug and play. Does anybody know for sure?

The most likely problem with your RECM is water ingestion. Has the leak been corrected yet? If so, is it possible to open the cover on the RECM to fully dry it out? If the housing can be opened, I'd try that first before considering a replacement. Might save you a lot of money and aggravation.