Use your head

Car Mechanics (UK) - - Editorial -

Up un­til re­cently, buy­ing a used car with an il­lu­mi­nated en­gine man­age­ment light was fine for many of us, as it meant we could hag­gle for a bet­ter deal on the ask­ing price. That’s all changed since the MOT re­vi­sions from May this year, where there is now a lit­tle line in the MOT man­ual, un­der

Sec­tion 8 Nui­sance, that stip­u­lates that an ‘En­gine MIL in­op­er­a­tive or in­di­cat­ing a mal­func­tion’ is a MA­JOR fault. In other words, an in­stant MOT fail­ure, re­gard­less of the rea­son for it.

This has made buy­ing cars with an il­lu­mi­nated mal­func­tion in­di­ca­tor light (MIL) a whole dif­fer­ent ball game – if the MOT is loom­ing. The seller may have to drop the value sub­stan­tially or else the ve­hi­cle may well be un­sellable un­til the fault – what­ever it may be – is fixed.

Our di­ag­nos­tics fea­ture, start­ing on page 6, is based around this change in the MOT. It’s also an ac­knowl­edge­ment that a fault code reader is now an es­sen­tial com­po­nent of every mo­torist’s tool­kit. With­out one, we ei­ther have to ask some­one who does to check for fault codes for us, or else make a po­ten­tially costly visit to a garage for in­ter­ro­ga­tion of the ECU.

As we all know, a MIL can throw up a num­ber of trou­ble codes listed un­der the EOBD for­mat (which came into force from Jan­uary 1, 2001, on petrol en­gines and Jan­uary 1, 2004, on diesel units). Fig­ur­ing which of these codes di­rectly re­lates to the prob­lem isn’t so straight­for­ward. This is why our fea­ture also hopes to teach you the im­por­tance of not just read­ing the codes, but cor­rectly in­ter­pret­ing them, too.

This was brought home to me when I be­came aware of a flash­ing glow plug lamp on my 2003 Skoda Oc­tavia TDI last month. The car was per­form­ing as usual, so it wasn’t im­me­di­ately ap­par­ent what the prob­lem might be.

Luck­ily, I re­mem­bered an in­ci­dent some years pre­vi­ously, when a MIL led a main dealer to re­place the ECU at great ex­pense and that hadn’t re­solved the prob­lem. CM’S di­ag­nos­tic guru at the time, Si­mon Ashby, was asked to find the cause of the MIL and he found that the rear brake lights were not work­ing.

When I reached my des­ti­na­tion, I found a will­ing per­son to press the Oc­tavia’s brake pedal and yep, both brake lights and the high-level lamp were non-op­er­a­tional. Later, my Foxwell code reader found a few codes I hadn’t re­alised were stored in the ECU, along with one tell-tale code for the brake light switch. A gen­uine part from the Skoda dealer was or­dered – a nice £12.10 fix. The glow plugs, of course, were fine.

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