Xantia V6 Lambada sensor wiring

[yannbeam]

Hi all. Could anybody tell me what wires go in what holes on the four pin plug for the oxygen sensor on a MK1 Xantia V6 ? While trying to undo the plug so I can remove the sensor, I have mnaged to pull the plug off the wiring loom. So now I have four wires dangling down and I'm not sure which order they go in !
I have a wiring diagram but it only lists codes, not colours.

The wire colours are yellow, orange, green, and red

Any help greatly appreciated

[xantia_v6]

I don't think that the colours are going to help, as Citroen seem not to have specified them.
I think that you are going to have to identify the 2 shielded signal wires that go to the ECU and the 2 heater wires that go to the fused supply and ground.

On the sensor, the polarity of the heater wires is not important, nor (as far as I am aware) is the polarity of the signal wires.

[white exec]

Mike,
Connection colours for #900 Oxygen Sensor are shown on Gabor's (XM V6) circuits, for each of the V6 engines.
Might help?

[xantia_v6]

I have the diagram for the Xantia Mk1 ES9, but it does not show wire colours:
The Lamda sensor is item 1350.

[wheeler]

If you have page 2 of that diagram above it should show the wire colours.
Are you not able to see the codes printed on the wires?

[xantia_v6]

If you have page 2 of that diagram above it should show the wire colours.
Are you not able to see the codes printed on the wires?

Here are the other 2 pages, but I don't think that they add much, no colours that I can see:

[wheeler]

No doesn’t look like it in this case, on later PSA diagrams the second page normally shows the wire colour too.

[white exec]

As Mike said earlier, pins 3 & 4 are for the screened pair, so 1 & 2 are for the other pair.
Polarity of each likely not important.

Lord knows why cable colours seem missing from those diagrams; always present on earlier ones, and seem to be there later on as well.

Looking at your original photo, the wire colours just could be
red - green - orange - yellow/green
If they are that, they could be the same as this diagram (Gabor's, for XM) for ES9J4 V6 . . . #900 on the diagram

Might/might not help you to nail the connections.

[edit: diagram now corrected]

[yannbeam]

Thanks for that. The Knowledge on this forum never fails to impress !
I wanted to check the feed/earth for the heater circuit but access is severely limited on the V6. She failed the MOT on emissions and I'm having trouble getting to the bottom of it.

[xantia_v6]

The V6 Xantia is typically quite difficult to get through the fast idle emissions test, most of my V6s have struggled (I have had 5 cars with ES9J4 engines). The problem seems to be that the car is fitted with a rather large catalytic converter, but as the engine itself is fairly clean, the converter does not burn enough HCs to get hot enough to work properly. Typically the tester needs to run the engine at about 3000 RPM for about 2 minutes to heat up the cat enough, and then the exhaust emissions magically drop to zero.

Before going much further, you should get the exhaust checked on a 4 gas analyser which will tell you if the lambda is correct. If it is, then there is nothing that you can repair or adjust on the engine that will improve matters, it is just down to the catalytic converter.

Many of these cars have had the cat replaced due to this, but I would advise against this, as the replacements that you can buy now are not up to the job, and will fail after a year or two. If I ever do need to replace a cat, I will try to get a quality cat from another make welded into the Xantia pipe, rather than buying one of the cheap pattern replacements.

[yannbeam]

The MOT tester was really good. We got it 'proper hot' but it wouldn't drop low enough to pass. We came to the conclusion it's not running quite right, its definitely got a slight hesitation. I think it may be running slightly rich, but cant find anything wrong with it !

[xantia_v6]

OK, with that information, here are my suggestions:

Check for oil or water in the spark plug recesses, this will entail removing the inlet manifold. Water will usually kill the spark to one cylinder which is immediately obvious, but oil (depending on how dirty it is) can just cause an odd misfire. Which will make the O2 sensor see too much oxygen and make the mixture too rich. Failing ignition leads to the rear cylinders have also been known to cause a misfire.

Check the rubber cap which closes off the spare vacuum port on the rear of the inlet manifold. If it has split it can cause an uneven mixture and misfire. A leaking inlet manifold gasket would of course give the same symptoms.

Check the vacuum hose to the fuel pressure regulator (while you have the manifold off), as a leak here would cause a rich mixture.

Some numbers from Lexia would probably also help with diagnosis.