Xsara Picasso: EML and random fault codes

[Picasso-VTX]

This has been a long time coming. My car is a 2007 Citroen Xsara Picasso VTX, with the 1.6i 16v petrol engine, (TU5JP4). Over a period of a year to eighteen months the EML has come on and random fault codes have plagued this vehicle. The fault codes were mainly Oxygen sensor related both front and rear. At one point, to trace wires I removed the three ECU connecters. The middle connector was full of what appeared to be oil. It was clear and I thought possibly something Citroen put in situ to prevent corrosion, although the other two ECU connectors were dry. How wrong can you be.

To cut the story short, I have tracked the fault down to a faulty power steering pressure switch. I opened up the wiring harness to the ECU middle connector the sensors terminated were: multiway connector to the coil pack, the water temperature sensor, both oxygen sensors and the power steering pressure switch. The only sensor with pressurised oil behind it was the power steering switch. Oil had been wicked/pressurised into the wiring harness entered all the connectors to the above sensors and poisoned both Oxygen sensors. I have gotten through no end of O2 sensors because, as I changed them the EML and faults would clear and then re-emerge some miles later but with a different set of fault codes. When I disconnected the power steering pressure switch the connector was full of oil and the switch pins had oil oozing past them. There was no external oil leak just a stain on the switch mounting.
I could go on at length to the full story but lessons I've learnt along the way: from the Bosch website, O2 sensors do not like oil,WD40, or any other form of electrical cleaner on the connectors. It prevents air entering the sensor and ends up poisoning the sensor internal components as it wicks down the wires. O2 sensors, Bosch 0-258-006-028, FAE 77282, and Hella 6PA-009-165-681 are all compatible and fit both front and rear positions, although the Hella has a slightly shorter lead. I'm currently running a Hella in the front posiition and an FAE behind the catalytic converter. When changing the engine oil filter, cover the engine oil pressure switch with rag or tissue to prevent oil saturating the switch and penetrating through the sleeving around the switch. That's another story.

As an aside, oil wicking into harnesses is quite common with Vauxhall Astras & Corsas, Land Rovers with the TD5 engine, some models of Mercedes Benz cars and Honda CB750 engine stators. The same switch is fitted to a number of Peugeots, so something to watch out for.

Now, having replaced the switch, with a few hundred miles under the belt no EML, no fault codes and no pending codes either. Just don't give up.

[white exec]

Hi, and welcome to the forum.

Wicking of oil along a wiring harness has been written about before, iirc.
It will ring a bell with someone here, for sure, who will know more detail.
Well done in nailing the problem.

[wheeler]

Not a fault ive seen on a PSA car with oil, seen it plenty of times with coolant wicking up the wiring from a cracked coolant temp sensor & straight into the ECU, never any signs of external leaks.
Like you say the TD5 Landrovers are very common for this with the ECU filling with oil.