Fault code pending

Q: My 2007 Vauxhall Combo 1.3 CDTI van is showing the fault code ‘P0108, pending’ and when the little light with the spanner flashes, I lose power momentarily. If I stop and restart, it will go back to normal till next time. Has this got anything to do with the EGR valve? If so, can it be cleaned out or will it need replacing? Ray Dullick

A: Code ‘P0108’ refers to ‘Manifold Absolute Pressure/barometric Pressure Circuit High’. The code is triggered when the engine management system records a voltage reading from the MAP sensor that’s greater than 5V or higher than the normal standard. The voltage output is regulated by the recorded vacuum – the higher the vacuum, the lower the output voltage; at idle, the output reading should be around 1 volt. If the MAP sensor is not faulty, then the higher output voltage could be caused by positive pressure in the system, for example by a blocked EGR valve.

First, check the MAP sensor output voltage. If this appears to be within acceptable parameters, check and clean out the EGR valve, ensuring the solenoid rod inside the valve is clean. As the valve is electrically operated it may need replacing, but often a good clean will provide at least a temporary repair, confirming that the problem is with the EGR valve.

The third possibility is that the turbo actuator rod is sticking, so the turbo is unable to regulate boost pressure by releasing the wastegate. This can be checked by manually operating the actuator rod and checking the vacuum pipes and diaphragm.