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P0141 and strange o2 eading



Hi guys,

I have a strange problem, maybe someone has seen something like this before and can help me with some tips.

Clio RS 182, F4R 738, Siemens Sirius 34 ECU
I have a permanent Check Engine light with: P0141 Oxygen O2 Sensor Heater Circuit Malfunction (Bank1, Sensor2)

Both oxygen sensors are brand new Bosch ones, the resistance of the heater circuit measured and proven to be OK, 12 Volts are present in the wiring loom at the heater pins of the connector.

The downstream sensor provides uninterpretable signals (the upstream sensor seems to be fine), see attached graphs. After cold start, it sends constant 1.275 Volts, after about 10-12 minutes of driving it suddenly falls down to 0 Volts, stays there with little bounces below 0.2 Volts. When I clear DTC’s then the Check Engine light comes back at the second full operating cycle (with cold start and reaching operating temperature) at the exact moment when the downstream graph falls dows to 0 Volts.

If I disconnect the sensor, it immediately switches to 0.45 Volts fallback value, if I plug it back, it returns to the previous behaviour - so I assume the ECU perceives the signal wires and open circuits fine.

Some people say it’s because of the catalytic converter (Milltek), but I think in this case the downstream sensor would mimic the signals of the upstream sensor, not provide out of range values.

The ECU was mapped at one of the previous owners, but it was restored to the lastest OEM map before I purchased the car (at least I was told this happened).

Has anybody seen something like this before, do you have ideas what to check next?
Flashing an OEM map at the local dealer could make sense, or does it seem like an ECU hardware problem?

Thanks for your help!
 

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  dan's cast offs.
could be a wiring issue? post should be sat at 0.45v (can't remember exactly) what did you read codes with and any other codes?
 
could be a wiring issue? post should be sat at 0.45v (can't remember exactly) what did you read codes with and any other codes?

Thank you for your reply!

ELM327 + Torque, no other codes present. If I clear the code, it comes back on the second operating cycle.
 
  dan's cast offs.
torque is s**t!!!!!!!!! get it read with something decent, need to check other stuff for codes, don't be surprised if you have short on ac pressure sensor circuit.
 
torque is s**t!!!!!!!!! get it read with something decent, need to check other stuff for codes, don't be surprised if you have short on ac pressure sensor circuit.

It's OK to get it read with another device, but how does the O2 sensor relate to the AC pressure sensor circuit? Do they have a common wiring loom, fuse or something like that?
 
  dan's cast offs.
had issues with the loom on both circuits, didn't check the actual problem as the car had a few issues so it worked out cheaper to just swap for a known good loom. still got the faulty loom and will probably open it up one day.
 


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