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Upstream sensor died while driving?

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Upstream sensor died while driving?

Post by SvenGWK »

After my problem with false air has been solved, I did a somewhat longer test drive today.
At the beginning everything was great, but when I read out the ECU error log during a break there was already something stored in it.
P0131[O2 Sensor circuit low Voltage] was reported, a little later P0172[System too rich] was added. CEL is lit.
The car stinks of unburned fuel.
Long Term Trim is permanently at 25% now , the other Trim values are at 0.

I looked at the log of the trip and see that something must have happened along the way.
The voltage of the upstream sensor dropped off quite fast, then the Long-Term trim increased.
The voltage is really low: 30mV - often also at 0V - but the downstream sensor is nearly 1V.
I don't think a leaky exhaust could cause that. I can't hear any difference either. The car sounds the same as usual.
Uploaded the log of the trip where the error occurred: https://csvshare.com/view/E1TM5iyqE
I think the "turning point" came with measurement 862/863.

This measurement then shows the "result": https://csvshare.com/view/41JqDokcN
(There is a small error, Mass Air Flow is of course kg/h - not kg/s! :D )
The longterm trim was 25%.
The upstream sensor shows an extremely lean mixture, the downstream sensor an extremely rich mix.

Could I be right about the diagnosis that the upstream sensor perished?
Is it normal that these parts die so suddenly?
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Re: Upstream sensor died while driving?

Post by wizechatmgr »

Sounds to me that the sensor has indeed perished - but first I'd check the connections and make sure we don't have a wire broken or grounded out.
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Re: Upstream sensor died while driving?

Post by SvenGWK »

I rechecked today what the sensoor is now measuring.
Since the TRIM was at 25% I disconnected the battery. Afterwards I checked again and found that it measures normal values again.
After a short test drive, however, the values drifted back into the low range. https://csvshare.com/view/Vk1O4FecV
TRIM is still normal.
I think the sensor is broken and I should replace it.
The problem seems to be somehow temperature-dependent and I would also like to be able to push the pedal a little bit harder from time to time.

I can't see anything abnormal on the wires.
I suspect the defect is related to the fact that I have been driving with an extremely rich mixture for the last 1.5 years "thanks to false air". In town, by the way.
If it is actually still the originally installed sensor, it has now also accomplished 167000km. As I have read in the meantime, a defect under these conditions is nothing unusual.

I have Motronic 4.4 .
If I enter the combination "C70, MY98, Engine B5254T, M56", on the Website of my "Shop of Trust" , I unfortunately get more than one sensor listed.
There are sensors with 1, 2, 3 or 4 wires.
I suspect I need a sensor with 4 wires?
The sensors that i can see in the shop for my car as "Volvo Original" (BOSCH) have 4 cables. Part no is 9202719 .
This is the most expensive sensor that can be bought from this series: 124,50 €.
A quick search at other parts dealers shows significantly cheaper alternatives, e.g. a universal sensor by RIDEX for 33,98 € or parts by STARK, FAE, DENSO for almost the same price. There is also a universal sensor by BOSCH for around 50,00 €.

I always can't decide what to take for lunch in our canteen - I find it even harder to choose sensors.
Which one should i buy? Is the Motronic 4.4 choosy about the lambda sensor? Due to the fact that they all have the same part number, the characteristic curves should all be the same, right?
Last edited by SvenGWK on Sun Mar 25, 2018 12:22 pm, edited 1 time in total.
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Re: Upstream sensor died while driving?

Post by abscate »

It’s worth taking your old one off and getting then part number

Don’t go with aftermarket or universal on this part, I know they arent cheap but look at the reports of people trying this route first
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Re: Upstream sensor died while driving?

Post by sleddriver »

I went with a Bosch sensor after much research. Can't remember the details though as it was quite awhile ago. I've read that O2 sensors age (decline) and replacing the front can improve MPG and performance.
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