Crank­shaft sen­sor prob­lem

Car Mechanics (UK) - - Help! -

My Astra H (en­gine code Z18XER) is run­ning like a trac­tor. The only fault code I con­tin­u­ally have is the ‘P0335 Crank­shaft Sen­sor Open Cir­cuit’. I’ve re­placed the sen­sor and checked re­sis­tance and volt­age, but all is fine.

This has been a project car af­ter a pis­ton dis­in­te­grated on cylin­der No 4. The pis­tons had been re­placed with plus-sized items, so I as­sume it had cylin­der­head/ en­gine prob­lems in the past. Be­fore the pis­ton ex­ploded, if you kicked down on ac­cel­er­a­tor while driv­ing, a huge white cloud of smoke came out the ex­haust. Head gas­ket fail­ure, maybe?

I’ve since re­placed the bot­tom en­gine with stan­dard pis­tons and re­placed the cylin­der­head twice, yet still have this one fault code. I’m con­vinced it’s down to the crank­shaft pick-up ring, but this is a night­mare to ac­cess be­cause it acts as the rear crank­shaft seal, so it’s an en­gine-out job. How can one sen­sor cre­ate such prob­lems?

Mark An­thony Sum­mer­sett

The crank­shaft sen­sor pick-up may well be the prob­lem and is go­ing to take a few hours to re­place. I wouldn’t rec­om­mend us­ing a bud­get part, but rather go for a gen­uine or branded item. One pos­si­bil­ity – which is not pos­si­ble to check with­out re­mov­ing the gear­box – is that the sen­sor is not sit­ting per­fectly flat on the back of the en­gine. I have heard of cases where the lo­cat­ing tag on the sen­sor ring is slightly too wide and does not al­low the sen­sor to sit per­fectly flat. The small­est de­vi­a­tion from the cor­rect po­si­tion will cause a prob­lem. The torque set­ting for the sen­sor ring is 4.5Nm.

Hav­ing checked the re­sis­tance and volt­age, the prob­lem may not be with the sen­sor it­self. It would also be worth con­firm­ing the con­ti­nu­ity and re­sis­tance of the wiring be­tween the sen­sor and the ECU, to en­sure there is not a prob­lem in this area. Hav­ing elim­i­nated the wiring, I would then re-check the valve tim­ing, as this could also give the symp­toms you have, and as the cylin­der­head has been re­moved it is pos­si­ble that a slight er­ror has been made when tim­ing up.

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