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Oxygen Sensors - HELP PLEASE!


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I'm confused with the oxygen sensors.

I looked at RAVE and on section 19 page 14-> of the workshop manual it shows the Engine ECM connectors and what the relevant wires are.

Looking at the middle connector (red one) C507 it says the following pins are to do with the Oxygen Sensors:

Pin 8 - Bank B Upstream

Pin 17 - Bank A Downstream

Pin 33 - Bank B Downstream

Pin 34 - Bank A Upstream

I have a UK 1998 4.6 HSE which pins should have wires?

On mine Pin 8 and 17 don't have any wires going to them, pin 33 and 34 do have wires going to them.

I connected the Multimeter to the negative terminal on the battery then probed pins 33 and 34, 33 just stayed at 0 all the time, pin 34 varied whilst I was watching it went between 0.1 and 0.7 volts.

If it makes any difference the MAF is disconnected as I clean it (although it doesn't seem very dirty) - I have managed to start by applying some revs, as without revs when the MAF is disconnected it just dies, after a couple of seconds I can leave it to idle although the idle feels a little low.

I also tested pin 15 which is the TPS, that gave me 0.65 volts on idle going up as I revved, I then turned of the engine and tested full movement which appears to function perfectly with no dead spots all the way up to 4.57v

So questions are:

Should it just be pins 33 and 34 with oxygen sensors connected? (the upstream and downstream terminoligy has me confused!)

Does the fact that I can't get a reading from Pin 33 indicate that, that sensor is dead?

Does the Pin 34 reading look OK?

Thanks in advance

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If your Lambdas are the same as for the Classic 3.9 then they have three wires - this includes the heater feed for the Lambda as they need to be heated in order to output a voltage - if this pin 33 is for the heater element then it may be that the Lambda is not heating (faulty) and therefore will not operate properly - if at all.

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They are a 4 wire sensor, pin 33 is the output wire from one lamda, pin 34 is the output from the other. I have now got pin 33 working.

Pin 33 goes from 0-5v and all plugs on that side are black.

Pin 34 goes from 0-1v and all plugs look ok on that side

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I'm confused with the oxygen sensors.

I looked at RAVE and on section 19 page 14-> of the workshop manual it shows the Engine ECM connectors and what the relevant wires are.


(the upstream and downstream terminology has me confused!)

Upstream and downstream refer to the positions of the sensor in relation to the catalytic converter and the engine.

Upstream is between the engine and the cat, downstream is after the cat, and thus between the cat and the tailpipe.

By comparing the upstream and downstream readings the management system can report on the effectiveness of the cat.

The whole (economic) issue of cats is the principle reason I don't run 'modern' petrol engines, so my knowledge is not as extensive as it might be. While writing, and without consulting a manual, I'm not sure whether UK cars have both upstream and downstream sensors, but if they only have one (as I suspect) I don't know which one they have.

I suspect you have misread the pin numbers, or you are looking at a diagram of a NAS car. Some of the RAVE CDs available on the 'aftermarket' are for NAS vehicles, not UK or RoW vehicles.

If you want a comprehensive understanding of cats and oxygen sensors, look for a section normally ignored, titled in the Index as EOBD. If you are paying for it and spending time maintaining it, why shouldn't you have a comprehensive understanding?



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Thanks David,

I have since found out they only have the upstream sensors and the Rave Manual has errors in it! The pins are correct and are shown later in the manual correctly but on the earlier page they are labeled incorrectly.

I have also used my OBDII cable and checked the lamdas there which both appear to be functioning correctly.

Should have chance to have a good look over tomorrow - still got me stumped but I believe it's running on 7 cylinders

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