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lambda sensor fault?????

  Clio 182
Hi all
Am sure it is but just checking. Did a RSTuner cal the other day and the engine management light came on after. Had a look at the fault codes and there were none.
Asked fast chip if they had any idea what it may be but no joy.
Looking again today and there is a 02 sensor fault in the memory. Had a look at the live data and got this after 5 min of tick over.


Rear voltage sensor never changed from 409.92
Do i take it the after CAT lambda sensor is FUBAR?

Thanks for any help


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  Trophy #392
mine does exactly the same and its exactly the same reading,i also have the 'rear 02 sensor' fault, think its just a new sensor needed there pretty expensive though best price so far is GSF
  Clio 182
mine does exactly the same and its exactly the same reading,i also have the 'rear 02 sensor' fault, think its just a new sensor needed there pretty expensive though best price so far is GSF
Hi the rear almbda sensor voltage correct if continual the voltage(0,409Volt) because it's check the CAT correctly working. :)
  Clio 182
Have found this info but does not give the values for the rear sensor.
Anyone know what they should be?

Richness regulation
The oxygen sensor is reheated by the injection computer when the engine is started.
Heating the oxygen sensor is stopped:
– when the vehicle speed is greater than​
108 mph (180 km/h) (value given for information purposes),
– according to the load and engine speed.

The value read on the diagnostic equipment (except XR25) under the Upstream sensor voltage parameter
represents the voltage supplied to the computer by the oxygen sensor located upstream from the catalytic converter.
It is expressed in millivolts.
The voltage should fluctuate between two values during richness regulation:
150 100 mV for a lean mixture,
750 100 mV for a rich mixture.
The smaller the difference between the minimum and maximum values, the poorer the signal from the sensor (the
difference is usually at least
500 mV).

The value read on the diagnostic equipment under the Mixture correction parameter represents the average of the
richness corrections made by the computer in line with the richness of the fuel mixture seen by the oxygen sensor
located upstream of the catalytic converter.
The correction value has a mid-point of​
128 and limits of 0 and 255:
– value less than
128 = request for mixture to be made leaner.
– value greater than
128 = request for mixture to be made richer.
If the difference is small, check the sensor heater.

Richness regulation​

Richness regulation will start after a timed starting period according to the coolant temperature if the oxygen sensor
is ready (sufficiently warm).
In all cases, richness regulation should be active after​
2 minutes if the coolant temperature is above 70 C.
When the mixture regulation is complete the parameter value is
128. Refer to the richness regulation state on the
diagnostic equipment.

Unlooping phase​
In the mixture regulation phase, the stages of operation during which the computer does not take into account the
value of the voltage supplied by the upstream sensor are:
– at full load,
– under heavy acceleration,
– under deceleration with a no load signal,
– when the oxygen sensor is faulty.
In this case the value​
128 is displayed.

When the voltage from the oxygen sensor is incorrect (varying only slightly or not at all) during mixture regulation,
the computer will only enter defect mode if the fault has been recognised as present for​
10 seconds. In this case
only the fault will be memorised, the parameter: "Mixture correction" is
If an oxygen sensor fault is present and recognised and if the fault has already been stored, the system enters the
open loop mode directly.

  clio 172
yeah, rear lambda should read something like that, and front lambda should be jumping like crazy exactly like it does, always under 1.0
  Clio 182 Mondeo Ghia Est
Had the same fault and car failed it's MoT altho engine managment light wasn't on at the time. changing the rear sensor made no difference. moved the new one to the front as they are identical and that made no difference either. each time the lambda reading was 0.40 or so. I have a cat back Scorpion exhaust and the problem was a slight air leak at the joints. the oxygen is effectively leaking back to the sensor. Bit of paste around the joints and it was sorted, readin well within limits. Hope this helps someone as Isaw the same prob on numerous forums but never saw an answer.


ClioSport Club Member
  182 FFAT
I have something similar
I mapped the car using the RS tuner 2 days ago and then went for a drive. the next day after the emission light came on. I plugged the rs tuner and cleared it out but came back few hours later.
Is this a coincidence or can it be related to the mapping?
I used the performance cal (not the overrun map)