Fault code pend­ing

Car Mechanics (UK) - - Help! -

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.

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