I'm trying to help a garage customer of mine to sort an on going fault on this Corsa.

The car came to them about a month ago and had a Lambda and fuel trim fault. So without testing anything they threw both front and rear Bosch lambda sensors on it. Then the car came back with the same fault and they then replaced the sensors with genuine sensors. All seemed well until yesterday and the car was back in with the fault codes as listed above.

I popped in to have a quick look at the car to find the short term fuel trip at max 25% and the lambda not switching and flat lined a 0V when tested in OBD live data. I scoped the sensor and found that when measured across the black (live on scope) and grey (earth on scope) the sensor was outputting -0.6volts if you gave the engine a sniff of brake cleaner to make it bog the voltage would rise to +0.15 volts and this was then shown on the OBD live data as a rise from 0-0.15volts.

I then disconnected the O2 sensor and measured the output from the sensor with the engine running and we had about 0.35-0.4 volts engine running. Give it a sniff and it went up to 0.55volts.

The fuel trim fault codes P2191 and P0171 indicate the engine management is trying to add fuel due to a very low O2 reading and the fault codes P0130 and P0134 support lambda circuit issues.

I don't think I have ever seen a lambda sensor give a negative reading before does anybody have an idea why it would do this?