Nox Sensor P220A Fault Code

[Trickiedickie]

Nox Sensor P220A Fault Code

I have a 2016 Partner Tepee 1.6 Blue HDI DV6FD engine.

I now regularly get this fault code. P220A nox sensor 1, bank 1 supply voltage circuit malfunction. It is easy to delete the code with a cheap Elm reader or with Diagbox. I am looking for input from members who understand this kind of intermittent fault.

So it all started about 6 months ago and I deleted it with Diagbox. All was good for a couple of jouneys and it came back again. So after clearing it several times I went under the car and disconnected the wiring harness plug/connector and sprayed in WD40 then reconnected the plug and it was all good. The fix lasted about 5 months and all was good.

Then a month ago the fault came back so I cleared it with Diagbox. Then it kept coming back. I carried out the same proceedure with the plug/harness and WD40 but this time no fix.

For a month or so I have been doing a mixture of long and short jouneys, then clearing the fault with the quick easy to use Elm diagnostics tool and carrying on until the next time and by doing this I have come to realise there is a distinct patten of use for the fault to appear.

The build up to the fault goes like this:
Clear the fault, then engine off, then restart the engine and drive for 5 or 500 miles and all is good with no fault appearing. Then switch off and at this point all is good.

Again for the next trip I start the engine and do the same, I can drive 10 or 100 miles and all is good with no fault appearing. Then switch off and again at this point all is good.

But on the third time I start the engine within 2 or 3 miles the fault reappears. So then I clear the fault code and we can then go through exactly the same 3 stage process for the fault to then reappear.

So in a nutshell I can do 2 journeys of any distance but on the third journey the fault appears within a couple of miles or so. It is happening with a regular pattern!

It is easy to swap out the Nox sensor but I really have my doubts. I mean I can do 2 journeys of any distance but on the next trip I get the fault. How mad is that? How come I can drive 100's of miles with a supposed voltage circuit malfunction on a faulty nox sensor and I don't get a fault showing?

It can't be a bad cable harness plug/connector and I don't believe it is a real supply voltage error because the fault always appears on the third time engine start.

What do you guys think?

[mickthemaverick]

I am not certain about this by any means but I believe that the ECU behaves differently for different types of fault. Thus if a fault is likely to cause damage it will flag up the fault immediately and possibly go into limp mode and give Stop light etc. For less severe faults I believe it may count occurences to a preprogrammed limit and then bring on the fault to indicate a problem. If I am correct then it is possible that the ECU needs three fail conditions before flagging it up and hence the fault may be there all the time but is only flagged each time the preprogrammed limit is reached. Thus if you are happy about the wiring then I'd suggest it could be the sensor always giving a fault but only generating a fault on each 3rd occurence. I could of course be completely wrong and if so you can be sure that someone will put me right and help you at the same time!

[Trickiedickie]

@mickthemaverick
Thanks for your thoughts on this issue. I didn't think about the possibility of a preprogrammed limit which would explain the 3x start engine then fault occurence.

I am thinking it would be a good idea to check the voltage and data cables to the sensor. Also I am thinking of running the vehicle with the sensor disconnected. That would be, clear the fault code and disconnect the sensor and then see if the car produces a fault on the third start.

After doing all of that it looks like I will have to swap out the sensor to see if that is the real solution.

[Trickiedickie]

So I went under the car and tested the voltages with a multimeter with the results showing 12v for the supply and 2.5v for both canbus connections. So the culprit must be the sensor.

I removed the old sensor, which turned out to be tougher than I predicted, as the threads were well seized.

I fitted a new original PSA sensor part no. 9821120980 (the old part number was 9678570780).

Using Diagbox I cleared all the fault codes:
U029D 87
P2200 87

Then in Diagbox under repair I initialised the new sensor.

Done a few journeys now and all good so far.