From what I understand problem has to be located at
IL10 12-WAY / BLACK / ENGINE HARNESS TO FUEL INJECTOR LINK REAR OF ENGINE. Problem is that I cannot get to that on my own 🤣🤣

 

Excellent progress! Keep digging, sounds like you're getting close. If one of the 5V ref wires had a bare spot, rubbing against ground or another wire, that could be the issue. It could also be a connector with dirty or loose contacts, and moving the harness temporarily reestablishes a good connection.

For troubleshooting, can you reposition the harness so you get a consistent good voltage reading? Maybe something as simple as snaking a piece of cardboard next to the harness, for example. I wonder if the message could then be cleared. If so, then you'd know where to concentrate your efforts for a permanent fix.

 

PROBLEM SOLVED!! I finally reached the ecm and cleaned it. No result. But voltage was lower than 5v. So it crossed my mind another possibility (I should have think of it before). A relay with some wear, so not enough voltage to the ecm. That was it. Replaced the ecm relay with that one from wind washers and everything is back to normal. Could any one please advice on anything special I should do since I disconnected the ecm (I.e. it might has to re-learn some bits)

 

Good news!

You'll have cleared the fuel trims, OBD monitors, and various other learned things. They _should_ all relearn but you can use OBD to see if they do. Watch the OBD monitors / pending codes - you want P1000 to turn to P1111. You want LTFTs (hot engine,parked, at idle) to settle within about 5 of zero.

 

Absolutely stellar work! Glad to hear you've got the problem resolved.

Can you please pop off the plastic cover on the relay and post a picture? I wonder if it looks anything like this one (AC clutch) from my car:




It strikes me as unusual that the computer wasn't programmed to detect low input voltage. The only symptoms were the low reference (output) voltage and the one P2135 code. I think the TPS is still the most sensitive to low input voltage, and would set that code long before the others. I guess this shows that sometimes you have to read between the lines to get to the root cause. Glad you didn't replace the throttle body? And who was that mouth-breathing chucklehead telling you to chase after damaged wiring and unplug all sorts of stuff?

For any reset required, this may be applicable:

https://www.jaguarforums.com/forum/s...ection-176446/

 

All advices on this forum were very helpful (not from the repair stores). The process was very very educational. In a couple of days I will post the photo.
Thank you very much all of you.

 

Still loving it! I came up with a simple test for anybody else who comes across a similar problem and suspects the EMS control relay. Swapping the relay with a known-good unit is an excellent idea. It looks like a lot of current flows through that relay, and it controls a lot of circuits. If the relay's switched contacts (the connection between prongs #3 and #5) had failed, they may have overheated and damaged the sockets on the power distribution box. This quick test makes sure the relay is properly handling the current flow, and that there is no extra resistance in the sockets.

See figure 01.7 in the wiring diagram. The EMS control relay is R5 in the front power distribution box. The switched portion of the relay is circled in red:




To test, turn on the ignition. If possible, turn on the engine for maximum load through the relay, but this test should work even if the engine won't start. Connect the voltmeter leads to the two fuses as shown, and set your meter to VDC. Do NOT remove the fuses, just touch the meter leads to the recessed metal test pockets in the head of each fuse. It doesn't matter which side of the fuse you test, as long as the fuse is good.






With the ignition on, and current flowing through the relay's contacts, you should only see a very small fraction of a volt between fuses F9 and F38. If you see more than approximately 0.25 VDC, this means you've got excess resistance between those two points, and it's acting like a resistor and reducing the voltage that reaches the Engine Control Module (ECM). The most likely culprit would be the relay itself, so swap with a known good relay and see if that helps. Repeat the test with a good relay in case the old relay had arcing damage, which may have overheated the sockets in the power distribution box.

 

yup thatll do it. todays systems are pwm and networked with busses that send data via 1's and 0's so it you dont have the right voltages, things go bonkers. I found connector corrosion messes up systems as well so ya, CHECK THE VOLTAGE UNDER LOAD!