Faulty Oxygen Sensor On A 2.0 VW Golf 4

This story is just one example of a faulty oxygen sensor on a 2.0 VW Golf 4 that we were able to diagnose and solve. We received a call from a friendly young lady on a busy Thursday morning, it was 11am we were in the middle of quite a few big jobs. She was in a bit of distress having trouble with her Volkswagen Golf 4. She said the car is shuddering and running rough, she had been to 2 other mechanics over the week and they were unable to fix or diagnose the problem.We informed her that we specialise in Mercedes Benz, BMW, Audi and Volkswagen so are happy to have a look at it for her.

We booked her into Autoactive Mechanic Northshore on the same day at 1pm there to find out she was, just like many other new customers who came to us, recommended by one of our very valued customers. The car came in just after 1pm. With a fully booked schedule we did not get a chance to start looking at it until just around 2pm. First thing first was a road test to feel the shuddering and rough running. It was felt that the car was surging to the point where it was almost not drive-able. It felt like it could have been a fuelling problem.

Back To The Workshop

We scanned the engine electronics for faults. Two faults found:

  1. P0420 Catalyst Efficiency Below Threshold
  2. P0133 Oxygen Sensor Circuit Slow response B1 S1

The fact that Catalyst fault code is an emissions fault tells us it does not cause a running problem.Therefore the faulty oxygen sensor on a 2.0 VW Golf 4 is most likely the culprit.

We wasted no time started our Proof to Confirm diagnostic procedure. We started looking at the live data from the engine control unit. Turned out the faulty oxygen sensor on a 2.0 VW Golf 4 was stuck at 1.27V, with no fluctuation at idle or full throttle. The short term fuel trim was also at -20%. What does that mean exactly? OK, simply put, the oxygen sensor is telling the computer its running too rich and the computer is trying to reduce fuel to its maximum of -20%. Straight ahead the next step we knew would be nothing else but to replace the oxygen sensor first and then to road test again.

We called up the owner of the vehicle to tell her of our findings, the cost of repairs and also what component needed to be replaced first before any further diagnostic can be carried out if any. She gave us a go ahead. We immediately ordered in a Genuine Bosch oxygen sensor, which is the OEM oxygen sensor for Golf 4. After the sensor was fitted to the car, we reset all adaptations. Road test again and the car ran perfect just the way it should be.

It was now 3:45pm the same day, we called the customer to let her know of the successful out come and the car was pick up at 4:30pm. Although most of our services and repairs are by appointment only sometimes we are able to work on urgent fixes and we were pleased we were able to help.