When the customer bought this 2015 Toyota Aygo 1.0 VVTi in to me, the engine was running ok, but the engine management light was glowing brightly, indicating a problem.

The first move was, of course, to plug the Aygo into the diagnostic scanner to see what codes would be revealed. A couple of codes came up P0030 and P0031, the first indicating Heated Oxygen Sensor (HO2S) 1, bank 1, heater control - circuit malfunction and the second indicating Heated Oxygen Sensor (HO2S) 1, bank 1, heater control - circuit low.

Although both of these faults could have been caused by a faulty sensor, it is always good not to jump to conclusions and to test the circuit involved before replacing the sensor. Although in this case, if the sensor had been replaced, the problem would have been cured. This was not because the sensor itself was faulty, but because the loom between the sensor and the plug (which would have been replaced) was the source of the problem.

Where the wiring loom had been fixed to the securing clip and held against the cylinder head, it had rubbed through. These sorted wires were the reason for the illuminated light and the trouble codes.

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