My 2004 Vanden Plas 130k miles is in limp mode. I currently have the following codes po351.354,356,357, and 1367also 1646. I replaced the relay and the motor ran fine for about 5 minutes then went back to limp mode with no change in codes. I am currently trying to remove the ECU cable to check for water damage, just waiting on prime delivery for the t-30. Please any ideas would be helpful. I would like to say that the week prior I would get the restricted performance pop up for a few seconds during trips, before full limp mode.

 

They look fairly consistent so probably not the cable - but worth checking.

P1646 is likely the sensor, just change it unless you want to spend ages hunting around.

Very odd to get so many all at once.

Can't recall anyone getting P1367 but check via Search

 

Take a look at the wiring below - 1,7 same bank, 2,4 same bank. They are all spliced together within the wiring harness. Possible you might have a wiring harness issue with this splice ( I have seen where the fail due to heat over time ) or possible chaffed. I have also seen the PCM's give problems internally with the injector circuits and coil circuits.



As for the Oxygen sensor code, I would agree with JagV8 that its most likely the sensor that is faulty.

Have you done any wiring checks for the coils, etc? Maybe try labelling the coils, and swapping them to different cylinders to see if the DTC moves with the coil?

 

You may also have a faulty circuit board. I have a 2001 Mercedes SLK that was throwing lots of codes and limp mode. After replacing parts and sensors I finally found a post on a forum that said the soldering joints on the circuit board develop hairline cracks. $250 at the wrecking yard (instead of $4,500 at the dealer) and 15 minutes to replace it, everything cleared and it has run happily ever after. I've not yet encountered that problem with my 2004 XJ6, but I would not be surprised to learn that circuit board soldering is a generic issue when cars are nearing two-decades old.

 

So I ordered the 02 units both up and downstream. The car was starting but while I was moving it to get it up on the ramps it cut off and now won't start. It will crank. I took the batter in to have it fully charge. When I put it back in the car cranked but to no prevail. I think I should pull the ECU and have it repaired I DON"T KNOW HELP!!