Technical Two failed O2 sensor - one is stuck

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Technical Two failed O2 sensor - one is stuck

MK2lover

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Joined
Sep 12, 2016
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41
I recently got:
P0141 (post cat O2 sensor heater control circuit malfunction)
P0130 (pre cat O2 sensor circuit malfunction)
And the car was doing about 12l/100km.

I replaced the pre cat O2 sensor and the fuel economy is back on track. I due however still get a P0141 error after driving for a while.

Now the obvious solution is to also replace the post cat O2 sensor. However, it is rusted completely into the exhaust and I doubt i can get it off without ruining the exhaust. I also find it very unlikely that the two O2 sensors should fail simultaneously. Could the problem be something else or does someone have an idea on how to remove the rusted sensor? I am currently running the car without the exhaust heat shield (since it is rusted into oblivion) - could this cause the "heater control circuit malfunction"?

I've attached the Pre and Post cat sensor readings.
 

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Joined
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The pre-cat sensor is the one that does all the work. Your code suggested that one's sensor circuit was dead, and replacing it seems to have fixed that issue.

The post-cat sensor is there to confirm that the catalyst is doing its job. The code you quote states 'heater circuit', so that sensor needs replacing too, although less urgently.
The sensors need to be hot to work properly. They have a heater in them to get them hot, so they work quickly, without having to wait for the hot exhaust to heat them. The heaters then shut off after a short time. Without the heater, it just takes longer before the senosr can give good readings. Once it is hot, from the exhaust, it will function properly. If you have no other codes, the catalyst is working fine, and so is the sensor itself, once hot. You may suffer a slight iincreasein fuel consumption until it is replaced.

They grow in.
Ideally you need the proper socket for the sensor, to avoid breaking it, although a normal ring spanner will work, if you're careful.
Soak it in release agent. Plus Gas is good, others are available, but ensure it is proper release agent, not WD-40 or equivalent.
Wait a few hours, soak it again. Repeat.
Run until hot. Soak it again. Whilst hot, try to remove it. They are easier when hot, beware 1st degree burns. Difficult to do with your stout leather gardening gloves on, but something like that may be necessary. If you have access to an impact gun, that might help 'shock' it off.
Once out, do not fit the new one until the system is cold, otherwise there is a high risk of you overtightening it, and it'll never come out again.
 
OP
OP
M

MK2lover

Member
Joined
Sep 12, 2016
Messages
41
The pre-cat sensor is the one that does all the work. Your code suggested that one's sensor circuit was dead, and replacing it seems to have fixed that issue.

The post-cat sensor is there to confirm that the catalyst is doing its job. The code you quote states 'heater circuit', so that sensor needs replacing too, although less urgently.
The sensors need to be hot to work properly. They have a heater in them to get them hot, so they work quickly, without having to wait for the hot exhaust to heat them. The heaters then shut off after a short time. Without the heater, it just takes longer before the senosr can give good readings. Once it is hot, from the exhaust, it will function properly. If you have no other codes, the catalyst is working fine, and so is the sensor itself, once hot. You may suffer a slight iincreasein fuel consumption until it is replaced.

They grow in.
Ideally you need the proper socket for the sensor, to avoid breaking it, although a normal ring spanner will work, if you're careful.
Soak it in release agent. Plus Gas is good, others are available, but ensure it is proper release agent, not WD-40 or equivalent.
Wait a few hours, soak it again. Repeat.
Run until hot. Soak it again. Whilst hot, try to remove it. They are easier when hot, beware 1st degree burns. Difficult to do with your stout leather gardening gloves on, but something like that may be necessary. If you have access to an impact gun, that might help 'shock' it off.
Once out, do not fit the new one until the system is cold, otherwise there is a high risk of you overtightening it, and it'll never come out again.
Thanks a lot for the answer. I will try to get an additional sensor asap. Meanwhile, should there be any concerns about driving the car? I'm worried about destroying the cat. The fuel consumption is back to normal.
 
Joined
Feb 22, 2004
Messages
9,099
Location
Faringdon, Oxfordshire UK
Thanks a lot for the answer. I will try to get an additional sensor asap. Meanwhile, should there be any concerns about driving the car? I'm worried about destroying the cat. The fuel consumption is back to normal.
No concerns. The pre-cat sensor is the important one, which is now working as it should. The post-cat is just an auditor, which due to the heating element beng dead, will just take longer to warm up and report properly. Only effect will be the code you've already got.
 

iABDOzz

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Feb 12, 2022
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13
Location
Egypt
i had the same problem with post cat O2 sensor bought a new one and zip tied it on the side of the coolant line for a year now, couldn't get the old one out - the car gets 17km/L - check engine light off.
 
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Location
Helsinki
i had the same problem with post cat O2 sensor bought a new one and zip tied it on the side of the coolant line for a year now, couldn't get the old one out - the car gets 17km/L - check engine light off.
There must be a way to get it out. Weld a piece of metal to it to make a spanner and get sufficient leverage and/or beat the hell out of it? Heating the exhaust and cooling the sensor will help break it free.
 
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