Possible ECU problem
A friend has asked me to look at his 2012 Nissan Micra 1.2 three-cylinder petrol. Over the past 18 months, the malfunction indicator light (MIL) has been illuminating, each time leaving this code: ‘P0036 O2 Sensor, Bank 1, Sensor 1 – voltage out of range’. Live data shows voltages of 2.250V at the pre-cat sensor, with a more usual 0.280V at the post-cat sensor.
The pre-cat sensor has now been changed three times, twice using secondhand genuine Nissan sensors. The first of these lasted almost a year. The owner then fitted a new aftermarket one. Initially, all was well, until I stopped the engine during a test-drive and checked for any new codes. All of a sudden, the MIL was on again and showing the code ‘P0031 O2 Sensor Bank 1, Sensor 1 Heater circuit’. It came back instantly after clearing. Live data from the precat sensor still shows 2.250V, irrespective of the throttle setting.
I’m beginning to suspect an ECU fault and have the owner’s permission to get it tested. I would also like to check the Lambda sensor wiring. What pins from the ECU govern it? I need to test both the heater and signal circuits.
The other thing that seems odd is that I can interrogate the ECU without switching on the ignition. Is this normal for a Nissan? Also, any time I connected my code reader previously, it worked first time. However, following the test-drive, it took three attempts! William Bamber The code ‘P0036’ refers to a circuit malfunction, while the later code ‘P0031’ indicates a circuit short to earth. With this in mind, your first move should be a continuity check between the ECU and 02 sensor to ensure that the source of the problem is not within the wiring loom. The signal circuit wires from the ECU are number 5 (green wire) and number 35 (blue wire). The heater element is fed from number 35 (yellow) on the fusebox relay plate and controlled by number 33 (pink) on the ECU. If the continuity checks on the wiring loom do not highlight any problems, I would send the ECU for testing.
The wiring diagram I have does suggest that the datalink controller has a live feed with the ignition off. The difficulty in connecting you have had on the last few attempts may suggest an ECU problem, but I would test the wiring circuits first.