Hello all,
I have a persistent lambda sensor failure P1647, even after replacing the sensor. I've swapped left to right by swapping the connectors and the 'failure' remains on the LH side and I have also 'beeped' out the harness between the connectors and the engine ECU.
I don't get any reduced performance message or MIL light, but I do get a slightly lumpy tick-over and it doesn't feel like I'm getting as much out of my considerable fuel bill as I should.
So I'm thinking the engine ECU is maybe faulty. I currently have the LNF1410AD - and on eBay I see may other types with different final 2 letters. Does anybody know which I can go for on my 2000MY XJR? (UK)

 

Some of the options are
wrong sensor replaced
new sensor is wrong type
new sensor is faulty despite being new - does happen
connector/wiring issue - beeping out is a start but not enough
PCM fault - send for test/repair

 

Thanks, JagV8, but I still suspect the ECU because in swapping left-right the fault remained as P1647 even when the sensors were the other way round. This leaves either the harness or the ECU. Then using an oscilloscope I measured equivalent voltages at both sensor pins at the ECU so I'm fairly confident the harness is ok.
I've taken a punt and just ordered an LNF1410AE off of the ebay, so we will see what happens when I swap that out. I'm hoping the move from AD to AE was innocuous.

 

Tom, I am afraid you are right, assuming the heater circuit is working. Have yu measured the heater voltage in both positions?

 

Yes - all heating seems to be operational.
When you trace real-time O2 signals through OBD, they seem to track left and right following each other, but then occasionally the LH goes bananas. So I suppose there is still the risk that the harness has an intermittent fault.
I've got the new ECU on order now, so if it doesn't fix it by direct replacement, I'll do a test where I do an oscilloscope trace of the voltage in parallel with the diagnostic values reported by the ECU.

 

Is the VCATS final 3 digits the same??? (the /xxx suffix)
Are you able to perform 'immobilization-setup'???

There is more to replacing the ECM than just plugging one in.

bob gauff