This vehicle was delivered from another workshop with the engine running issues of poor idle quality and high emissions. The 2005 Micra 1.4 fitted with a CR14DE engine had previously had the upstream Lambda sensor replaced, due to a fault code for O2 sensor signal P2274.

After the first workshop could not identify the root cause of this reoccurring fault, it was sent to a second garage for more investigation.
And after some further testing, they concluded the O2 sensor was still the issue and was replaced a second time. The fault remained.
 
It was then the Helpline was called to assist with the diagnosis and repair. We asked for the lambda sensor signal to be tested with a scope. In doing this, we found that the signal was switching in the low range 0.1 volts to 0.45 volts.

The heater circuit was checked, and had a healthy battery supply. The ground for the heater was also working correctly.
Then we asked for the sensor ground to be scoped, and this is when we found 0.25 volts present on the O2 sensor earth. Testing the sensor earth at the ECM multiplug still showed the high voltage drop on the earth return line.

This is a known problem for the Nissan K12 Micra and an internal issue within the ECM is the root cause.

However, a fix has been found. Externally grounding the Lambda sensor loom rectifies the issue, and allows the Lambda signal to return to the correct level. With this fix, the emissions settles back to the correct levels and the idle improves.

To join the Autobiz Helpline, call 01-905-9500, and then press 2, for further information.