Hey I own a Jagaur XK8 2001 Coupe,

I've made a few posts regarding the issue but this post will have all the updated info on the issue, at this point I think I know the issue but want some other enthusiast and techs opinions.

This code has been here since the car arrived 2 months ago, I've replaced a lot of modules on the car as in the past they were fried, from chairs to the SLM. I mention this because a mechanic who touched this car with the previous owner fried things when putting incorrect fuses and a bad alternator with janky wiring.

Now leading up to my end thoughts, I replaced the 02 sensor with 3 brand spanking new 220$ upstream sensors (Denso) from rock auto, all did not work. The heater elements in them I tested worked and they gave data as I did a bench test. Each time the code came back after clearing and driving the car for a week. Each time..

After, I tried thinking outside the box, someone gave me the workshop manual to start doing some tests. All the tests centered around testing the wiring harness for continuity had a result 0.3 ohms, passing the test amongst all 4 wires. All the codes testing the connection that went through testing the car with ignition on with the ECM connected gave odd results, sometimes this number, sometimes another but inconsistent, according to the manual the lack of detail in the instructions it makes it hard to say yes or no so I made it inconclusive.

I then had an idea and removed the 02 sensor (was really difficult as its under the coolant reservoir and put it in the passenger side (p1646))) and the code still persisted, I put it back where it came from (driver side) and it still worked. it was not the sensor...

So with that being said, I'm lead to believe there's a short in the ECM, all wires for the upstream are good going to the ECM, and 02 sensor is good. Is it even possible that the ECM just created a short in itself or possible during the past attempts at working on some electrical parts of the car with past owners? It looks too clean around the ECM and the warranty label is untouched so it's never been opened either. and when testing the system for emissions it always fails as 02 sensor and cats are subject of failure.

I think my next step should be removing the ecm opening it up and checking for shorts. Just looking for opinions first.

 

Output semiconductors can fail.
I had a customer car with a bank 1 VVT actuator fault.
Another shop ran a wire STRAIGHT to the VVT actuator from the ECM.(no change)

The wiring and connectors were all good as well as the actuator itself.

Turned out the internal ECM output circuit was faulty.
Replacement ECM and IMMOBILIZATION SETUP, the car was fixed!

 

Interesting.
This was actually an issue with the other modules as well. Most notable the chair modules. Your response motivates me more to rip the ECM out and check the semi conducts as per the diagram for the ECM. T

 

If the MOSFET (NEC K2498, T410 (I think) on the heatsink near EM85 connector) that activates the upstream bank A heater has failed (which normally is really unusual, but if you have had power overloads and spikes, I suppose it is possible), then it might be possible to verify this by looking at the voltage on pin1 of the heater (RU color) which goes to EM85-01 on the ECM. I think it should be pulled low (0V, i.e. Ground) when the heater is activated, and will float high (~12V - battery volts) when it is not activated. However, since the ECM will turn the MOSFET on and off with a duty cycle, it will probably be too quick to measure the on/off cycles with a multimeter (easy with an oscilloscope, but obviously most people don't have one) - I don't know the time period of the on/off cycle/PWM since I have never had cause to look at it. Various testing concepts using LED, or light bulb, etc. can be hooked up and might indicate a fault, assuming you don't have a scope.

With IDS you can monitor the O2 upstream sensor reading, but if there is a trouble code then I don't know if IDS and/or the ECM will allow the PID to be read.

Or you can try another ECU, but that is more expense and you need IDS to do the IMMO setup per Motorcarman.