FAIL­ING IG­NI­TION COILS

Car Mechanics (UK) - - Electronic Diagnostics -

If the en­gine is run­ning roughly or mis­fir­ing, pos­si­bly to the ex­tent that it is

ef­fec­tively un­drive­able, and the en­gine warn­ing lamp is il­lu­mi­nated on the dash, with a cylin­der-spe­cific fault code stored, this points to ig­ni­tion coil fail­ure.

If pos­si­ble, carry out a full fault code check of the en­gine con­trol unit (ECU) – you will al­most cer­tainly find a stored fault code re­lat­ing to a mis­fire spe­cific to a par­tic­u­lar cylin­der. So if the fault is in cylin­der No 1 the code would be ‘P0301’; ‘P0302’ would in­di­cate cylin­der 2, and so on. Also, if avail­able via the di­ag­nos­tic tester in ‘ac­tu­a­tors’, you can switch the fuel in­jec­tor off/on to see if the mis­fire dis­ap­pears on that cylin­der. It’s worth

not­ing that any ba­sic fault code reader can read en­gine faults if the warn­ing light is il­lu­mi­nated, but a more so­phis­ti­cated tool is needed for ad­vanced pro­gram­ming and other ECU checks.

We have come across a Qashqai fit­ted with al­legedly gen­uine NGK spark plugs bought via the in­ter­net, which turned out to be fake units that ended up burn­ing out two coils.

A quick test that can help di­ag­no­sis is to swap the coils be­tween cylin­ders, to see if the fault moves with the dodgy coil. An ad­di­tional check is to look for signs of burn­ing or a smell of burnt plas­tic.

You should al­ways re­new ig­ni­tion coils in com­plete sets. If one coil has failed, it’s highly likely that the re­main­ing ones won’t be far be­hind.

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