Replacing W124 Lambda sensor

5907

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Further to my problems with a lack of power once the engine is warm, I'm now pretty sure that it's the lambda sensor that's the problem; I tried a new MAF and new spark plugs / air filter but still no improvement, and there are several fault codes relating to the lambda system.

How hard is it to change the lambda on a W124 estate? Could I do it myself or should I take it to a garage?
 
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5907

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bump......
 

Number_Cruncher

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>>there are several fault codes relating to the lambda system.

Be careful that you are not shooting the messenger!

If there's a fuelling fault which makes the fuelling either very rich, or very weak, then you would get oxygen sensor fault codes. i.e., it's possible that the lambda sensor is working correctly.

The fault codes are the beginning of the fault finding process, not the end.
 
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5907

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>>there are several fault codes relating to the lambda system.

Be careful that you are not shooting the messenger!

If there's a fuelling fault which makes the fuelling either very rich, or very weak, then you would get oxygen sensor fault codes. i.e., it's possible that the lambda sensor is working correctly.

The fault codes are the beginning of the fault finding process, not the end.

Yes; but I've already eliminated the MAF, spark plugs, air filter etc.

The lambda makes perfect sense, since it only loses power when it's up to temperature, it pulls like a train when it's cold and idles smoothly. Once it's warm, it has no power and the idle sometimes hunts up and down.

I'm getting the following codes:

9 O2S 1 (before TWC) - voltage too high, circuit open or voltage implausible

13 O2S (Lambda) control system operating at rich or lean limit

The next logical step is to try the Lambda.
 

Number_Cruncher

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The next logical step is to *test* the lambda sensor while also measuring the mixture via the exhaust gas.
 
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5907

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The next logical step is to *test* the lambda sensor while also measuring the mixture via the exhaust gas.

But what's the point? A new sensor can be picked up for £25 or less; I may aswell change it while I'm under there, since I don't know how old the current one is.
 

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You may find that the connections (under the drivers carpet) have corroded.
 

The Crooner

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I've done it.

The wiring does through the floor pan to a connector under the drivers seat. You will need to remove the drivers front carpet to get easy access to it.

The lamda itself is probably rusted into the exhaust under the car. Lots of patience and penetrating fluid - dont skimp, buy Plusgas, and it came out.

BUT - the new one is in but will never come out again as the threads in the exhaust boss were toast. I put exhaust paste around it to ensure it was sealed.

I recommend first that you probe the wires under the drivers seat and see if its working - Malcolm will come along and give you the readings. Second, dont buy a £25 lambda, at least get a decent make, or an original.

I got my from Lambda Power http://lambdapower.co.uk/ they delivered quickly and it was an NKG.

No special tools are required.

Tony
 

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Little tip, when removing the lambda sensor wait till the system is cold. So much eaiser to remove when it cold.

sTeVe
 
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5907

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I've done it.

The wiring does through the floor pan to a connector under the drivers seat. You will need to remove the drivers front carpet to get easy access to it.

The lamda itself is probably rusted into the exhaust under the car. Lots of patience and penetrating fluid - dont skimp, buy Plusgas, and it came out.

BUT - the new one is in but will never come out again as the threads in the exhaust boss were toast. I put exhaust paste around it to ensure it was sealed.

I recommend first that you probe the wires under the drivers seat and see if its working - Malcolm will come along and give you the readings. Second, dont buy a £25 lambda, at least get a decent make, or an original.

I got my from Lambda Power http://lambdapower.co.uk/ they delivered quickly and it was an NKG.

No special tools are required.

Tony

I'm not going to pull up any carpets; I'll probably cut the wires at the sensor and connect them to the new one under the car.

And I've heard good things about the cheap eBay ones, so I'll probably go for one of them.

Thanks for posting your experience though, I hope mine isn't rusted (it doesn't look like it).
 
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5907

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You may find that the connections (under the drivers carpet) have corroded.

I don't think so; it's an old sensor which I doubt has been changed in the last 50k miles, so no surprise if it has failed.
 

The Crooner

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I'm not going to pull up any carpets; I'll probably cut the wires at the sensor and connect them to the new one under the car.

And I've heard good things about the cheap eBay ones, so I'll probably go for one of them.

Thanks for posting your experience though, I hope mine isn't rusted (it doesn't look like it).

The signal levels involved in these circuits are small and you should not introduce any extra unnecessary joints.

It takes two minutes to lift the front carpet.

If the job is worth doing I would politely suggest that you do it properly.

Tony
 
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5907

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The signal levels involved in these circuits are small and you should not introduce any extra unnecessary joints.

Other people have done it this way without any problems.

It takes two minutes to lift the front carpet.

And two days to get it back into place? the carpets in W124s do not like being moved, they never go back into place properly.
 


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