Sud­den power loss

Car Mechanics (UK) - - Tales From The Workshop -

This 2005 Audi A4 1.9 TDI was run­ning around quite hap­pily un­til it ap­proached an in­cline, when the owner started to feel a dis­tinct lack of oomph. No EML was il­lu­mi­nated and the en­gine didn’t tech­ni­cally en­ter ‘limphome’ mode, but it had cer­tainly lost power.

Many mo­torists are un­der the mis­con­cep­tion that plug­ging in a scan­ner will in­stantly di­ag­nose all prob­lems, but when no codes are in the sys­tem (and some­times even when they are) this is not the case. How­ever, we did have a good idea of the source of the prob­lem with this Audi, and a sim­ple test proved us right. By un­plug­ging the air mass sen­sor and giv­ing the ve­hi­cle a quick spin round the block, we found that power had re­turned. This is not a de­fin­i­tive test, but very of­ten when the air mass sen­sor fails it will limit the power, and un­plug­ging it will re­move the re­stric­tion. Un­plug­ging will also il­lu­mi­nate the EML, which we ex­tin­guished af­ter re­new­ing the sen­sor.

Un­plug­ging the air mass sen­sor con­firmed that it was faulty.

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