2003 S Type ECM
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Junior Member
Joined: Mar 2026
Posts: 1
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From: MO
2003 S Type ECM
Hi new here as a last resort.
I search older treads and did not find anything.
History: I have 220,000 miles on it and lost compression in the #2 Cylender.
Car is in great shape, no rust, dents, etc.
I had a new motor (used with 70K miles on it), after installing, the #2 cyl is not firing (shop did all the checking of plugs, Injectors, etc).
I ok it to two other shops, all said the same thing, bad ECM. I took it to a Jaguar dealer, but they did not look at it, said it would not start so they could not check it. They also said there are no new ECMs so they can’t fix it. They just did not want to be bother with it. 3 other deals outright told they don’t work on cars that old, 10 years old is the oldest.
I purchased a used ECM, but no one can program it. What to do? I’m not a mechanic, 65 and on a fixed income and only have this one car. Spent $10K putting a ne motor in thinking this car will last me the rest f my life.
HELP.
Richard
I search older treads and did not find anything.
History: I have 220,000 miles on it and lost compression in the #2 Cylender.
Car is in great shape, no rust, dents, etc.
I had a new motor (used with 70K miles on it), after installing, the #2 cyl is not firing (shop did all the checking of plugs, Injectors, etc).
I ok it to two other shops, all said the same thing, bad ECM. I took it to a Jaguar dealer, but they did not look at it, said it would not start so they could not check it. They also said there are no new ECMs so they can’t fix it. They just did not want to be bother with it. 3 other deals outright told they don’t work on cars that old, 10 years old is the oldest.
I purchased a used ECM, but no one can program it. What to do? I’m not a mechanic, 65 and on a fixed income and only have this one car. Spent $10K putting a ne motor in thinking this car will last me the rest f my life.
HELP.
Richard
Joined: Mar 2015
Posts: 45,578
Likes: 4,665
From: Dural, Northwest Sydney. Australia.
Welcome aboard Richard, here’s a link to the S Type section where you can ask your questions https://www.jaguarforums.com/forum/s...ed-v8-x200-15/
Joined: Oct 2007
Posts: 120,859
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From: PHX some of the time
Welcome to Jaguar Forums Richard,
Good to have you with us.
Enjoy the forum.
If you haven't done so already you should add your car details to your signature to help others to help you.
If you need help with getting around and using the forum follow this link for some help Forum Help
Good to have you with us.
Enjoy the forum.
If you haven't done so already you should add your car details to your signature to help others to help you.
If you need help with getting around and using the forum follow this link for some help Forum Help
Thread Starter
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Junior Member
Joined: Mar 2026
Posts: 1
Likes: 1
From: MO
2003 ECM
Hi new here as a last resort.
I search older treads and did not find anything.
History: I have 220,000 miles on it and lost compression in the #2 Cylender.
Car is in great shape, no rust, dents, etc.
I had a new motor (used with 70K miles on it), after installing, the #2 cyl is not firing (shop did all the checking of plugs, Injectors, etc).
I ok it to two other shops, all said the same thing, bad ECM. I took it to a Jaguar dealer, but they did not look at it, said it would not start so they could not check it. They also said there are no new ECMs so they can’t fix it. They just did not want to be bother with it. 3 other deals outright told they don’t work on cars that old, 10 years old is the oldest.
I purchased a used ECM, but no one can program it. What to do? I’m not a mechanic, 65 and on a fixed income and only have this one car. Spent $10K putting a ne motor in thinking this car will last me the rest f my life.
HELP.
Richard
I search older treads and did not find anything.
History: I have 220,000 miles on it and lost compression in the #2 Cylender.
Car is in great shape, no rust, dents, etc.
I had a new motor (used with 70K miles on it), after installing, the #2 cyl is not firing (shop did all the checking of plugs, Injectors, etc).
I ok it to two other shops, all said the same thing, bad ECM. I took it to a Jaguar dealer, but they did not look at it, said it would not start so they could not check it. They also said there are no new ECMs so they can’t fix it. They just did not want to be bother with it. 3 other deals outright told they don’t work on cars that old, 10 years old is the oldest.
I purchased a used ECM, but no one can program it. What to do? I’m not a mechanic, 65 and on a fixed income and only have this one car. Spent $10K putting a ne motor in thinking this car will last me the rest f my life.
HELP.
Richard
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Joined: Mar 2014
Posts: 26,695
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From: Tehama County, California, USA
Hello, Richard,
I'm sorry your kitty is having a little hair-ball fit, but members in the section where Jim directed you will be delighted to help.
Welcome to the forums from ElinorB.
(';')
I'm sorry your kitty is having a little hair-ball fit, but members in the section where Jim directed you will be delighted to help.
Welcome to the forums from ElinorB.
(';')
Veteran Member
Joined: May 2009
Posts: 27,473
Likes: 4,891
From: Yorkshire, England
It's unlikely to be the PCM (aka ECM), much more likely to be poor diagnosis.
What OBD II codes have you got?
(Each PCM is specially programmed and not trivial to change so forget the other one for now.)
What OBD II codes have you got?
(Each PCM is specially programmed and not trivial to change so forget the other one for now.)
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From: Oregon
Welcome to the forum. Sorry to hear your car is giving you such trouble.
Can you please elaborate on the timeline? Why was the original engine replaced? And most importantly, did the current problem only start after replacing the engine?
You didn’t specify the fault code, but I’m guessing it was P0302? That means low power in cylinder #2 (the last digit identifies which cylinder) compared to the others.
Did any of these shops run a compression test? You had mentioned that cylinder lost compression. If that’s true, you’ve got a problem on the mechanical side, such as a burnt valve, broken piston ring, etc. The control module won’t cause a mechanical problem like that, so I’m a bit confused.
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Junior Member
Joined: Mar 2026
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From: MO
The original engine had no compression in the #2 cyl, and 220,000 miles, I thought it would be best to get a new motor as the car is in perfect shape and my age. I do not know if the ECM problem was preexisting. One mechanic said the ECM probably knew the cyl was bad and accounted for it, but never reset. No one seems to know how to fix it.
it’s sad that the dealers will not work on it.
it’s sad that the dealers will not work on it.
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Joined: Oct 2012
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From: Oregon
Okay, peeling back some layers of the onion, so to speak. Hope you don't mind getting peppered with questions...
You said the original engine had no compression on #2. Was this confirmed with a test gauge? Or were you going by the check engine light and a corresponding fault code, such as P0302? And what about the replacement engine? Has the suspected low compression been confirmed with a mechanical gauge?
Were any parts swapped over to the replacement engine? For example, maybe the donor's wire harness was in poor condition, so the original was swapped to the replacement engine. Likewise with coils, injectors, etc.
If the original engine indeed did have low compression, the computer definitely would have picked up on that and set a P0302 code, and possibly others. Now as I understand it, when the computer is fully powered down (battery disconnected, for example), that fault code is forgotten. So are any adaptations the computer may have made to compensate. The computer goes through a relearn process when the engine is started again, using preprogrammed default values at first. Over several drive cycles, the outputs are tweaked, aka the learning process.
Now it's not impossible the computer is bad, but is extremely unlikely in my over-inflated opinion. These computers are typically very robust and not prone to such failures. I see it all the time where it's easy to blame the computer (self included), but it's usually not the case. Big clues will be if the suspected low compression in both engines has been confirmed with a mechanical gauge. And if parts were swapped from the original engine, I'd suspect something there long before condemning the computer.
You said the original engine had no compression on #2. Was this confirmed with a test gauge? Or were you going by the check engine light and a corresponding fault code, such as P0302? And what about the replacement engine? Has the suspected low compression been confirmed with a mechanical gauge?
Were any parts swapped over to the replacement engine? For example, maybe the donor's wire harness was in poor condition, so the original was swapped to the replacement engine. Likewise with coils, injectors, etc.
If the original engine indeed did have low compression, the computer definitely would have picked up on that and set a P0302 code, and possibly others. Now as I understand it, when the computer is fully powered down (battery disconnected, for example), that fault code is forgotten. So are any adaptations the computer may have made to compensate. The computer goes through a relearn process when the engine is started again, using preprogrammed default values at first. Over several drive cycles, the outputs are tweaked, aka the learning process.
Now it's not impossible the computer is bad, but is extremely unlikely in my over-inflated opinion. These computers are typically very robust and not prone to such failures. I see it all the time where it's easy to blame the computer (self included), but it's usually not the case. Big clues will be if the suspected low compression in both engines has been confirmed with a mechanical gauge. And if parts were swapped from the original engine, I'd suspect something there long before condemning the computer.
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Junior Member
Joined: Mar 2026
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From: MO
Yes, the original engine was check with a gauge.
no donor electrical parts, just brackets.
Aftet starting the new engine and running rough, the cylinder was checked with a gauge. I also have a Cat fault, but they also were replaced with all 02 sensors.
3 different shops confirmed the above.
I never saw the code, so I can’t answer to that.
no donor electrical parts, just brackets.
Aftet starting the new engine and running rough, the cylinder was checked with a gauge. I also have a Cat fault, but they also were replaced with all 02 sensors.
3 different shops confirmed the above.
I never saw the code, so I can’t answer to that.
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From: Yorkshire, England
Fault codes are NOT forgotten.
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Joined: May 2009
Posts: 27,473
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From: Yorkshire, England
Yes, the original engine was check with a gauge.
no donor electrical parts, just brackets.
Aftet starting the new engine and running rough, the cylinder was checked with a gauge. I also have a Cat fault, but they also were replaced with all 02 sensors.
3 different shops confirmed the above.
I never saw the code, so I can’t answer to that.
no donor electrical parts, just brackets.
Aftet starting the new engine and running rough, the cylinder was checked with a gauge. I also have a Cat fault, but they also were replaced with all 02 sensors.
3 different shops confirmed the above.
I never saw the code, so I can’t answer to that.
Many shops are frankly useless. Read the codes yourself.
You can tell they're useless as they're just part swapping at great expense and just hoping that's a fix.
Last edited by JagV8; Mar 8, 2026 at 09:41 AM.
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From: Oregon
Well, maybe a better wording would be something like faults presently not active are not displayed to the driver. I’m not familiar with dealer-level diagnostics, but there is probably some means to see historical faults.
Here is one common example: a loose gas cap. This will cause a fault in the test of the vapor recovery system, because the loose cap is sensed as a vacuum leak. The check engine light illuminates to alert the driver of the failed test. Retrieve the code, secure the cap (probably first item on the list of potential causes) and the problem is fixed. After several drive cycles with satisfactory tests of the system, the check engine light turns off automatically. That’s what I meant by “forgets”.
In this case, there was probably a P0302 code set with the original engine due to the low compression in #2. Once that was fixed (by replacing the engine!) the computer should no longer keep flagging that code if the new engine is mechanically sound. After the battery was disconnected, the code and check engine light should have been “forgotten”, or more accurately relegated to no longer active status.
On my ‘02, I can vouch for this behavior. I’ve had a coil fail and set P030X for the low power on that cylinder. I swapped with the coil from another cylinder. A new code was flagged for the new location of the suspect coil. Upon replacing the bad coil, all fault codes went away on their own. No reset needed.
Does an ‘03+ computer respond the same way? There are regulations behind the OBD II system, so I believe so. In that case, even if the existing computer set a P0302 code due to low compression, it should have cleared on its own. Makes me think there’s more going on than just one thing.
Here is one common example: a loose gas cap. This will cause a fault in the test of the vapor recovery system, because the loose cap is sensed as a vacuum leak. The check engine light illuminates to alert the driver of the failed test. Retrieve the code, secure the cap (probably first item on the list of potential causes) and the problem is fixed. After several drive cycles with satisfactory tests of the system, the check engine light turns off automatically. That’s what I meant by “forgets”.
In this case, there was probably a P0302 code set with the original engine due to the low compression in #2. Once that was fixed (by replacing the engine!) the computer should no longer keep flagging that code if the new engine is mechanically sound. After the battery was disconnected, the code and check engine light should have been “forgotten”, or more accurately relegated to no longer active status.
On my ‘02, I can vouch for this behavior. I’ve had a coil fail and set P030X for the low power on that cylinder. I swapped with the coil from another cylinder. A new code was flagged for the new location of the suspect coil. Upon replacing the bad coil, all fault codes went away on their own. No reset needed.
Does an ‘03+ computer respond the same way? There are regulations behind the OBD II system, so I believe so. In that case, even if the existing computer set a P0302 code due to low compression, it should have cleared on its own. Makes me think there’s more going on than just one thing.
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From: Oregon
Okay, that is important to know.
Definitely worth getting a code reader or simple scanner for yourself. We really need to know what codes are present. It’s all expensive guesswork to troubleshoot without them.
Definitely worth getting a code reader or simple scanner for yourself. We really need to know what codes are present. It’s all expensive guesswork to troubleshoot without them.
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Joined: May 2018
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From: california
You definitely need to find an independent shop that has sdd/ids software for jaguars. They can do a code scan and much more. Even a clear of ecm adaptations and possible reflash of ecm. I feel for you on tight budget and loving the car. Dont give up. Be aware that having that definite miss on the cylinder could cause cat converter damage. Does the check engine light ever flash. Keep answering the questions asked by forum members as best you can. Tons of knowledge on here and willingness to help.