Car won’t start after turning off engine

Post by **Tommyb 2579** » Sat May 31, 2025 12:19 pm

Hi all
Got a problem with my P reg 24v probe,can do a short journey or like I did last weekend Wigan/thornton dale/Newcastle and back to Wigan 400+ miles stop car won’t restart,until I disconnect the cps and then reconnect it she starts,do I need a replacement censor or is there something else what is causing this ,any help appreciated oh and thanks to Malc for telling me about the cps trick.

Post by **jrh** » Tue Jun 03, 2025 1:42 pm

Bit of Ju-Ju magic going on there.
The active pulse generated by the CPS only occurs at a time set by the gaps/magnets.
Once clean and hard contact, the connections will be fine.

Post by **Tommyb 2579** » Tue Jun 03, 2025 2:55 pm

Hi thanks for your message,so do you mean unbolt the cps clean the end of it and should be fine,not to clued up with probes yet being a retired roofer tell you how to fix a roof,coz there’s no wheels on it. Thanks again tommy

Post by **jrh** » Tue Jun 03, 2025 3:11 pm

Yes , items like the CPS , ABS and Hall Effect sensors generate tiny little pulses of electrical current . Dirty or loose connections are as bad as a broken wire.
A missing pulse can e enough to stop the whole system.

Post by **Tommyb 2579** » Tue Jun 03, 2025 3:12 pm

Cheers will let you know how I get on with it.

Post by **Tommyb 2579** » Thu Jun 05, 2025 8:24 pm

Hi John
Did exactly what you said to do and it’s running and stop/starting fine,been for a decent run no problems,
thanks for your help,only done it today has we’ve had the grandkids for a couple of days,so it looks like Tatton park
is on this weekend for the probe, but thanks again for your help it’s much appreciated and also Malcolm for putting up with my nuisance calls.regards tommy

Post by **Tommyb 2579** » Fri Jun 06, 2025 11:39 am

Oops spoke to soon,was running fine yesterday been to put petrol in this morning cut out again couple of miles from home,got it started again after 10 mins got onto drive at home cut out again,so I think back to the drawing board,Tatton is out of the question I think,no hard shoulder on motorway near me for 5 miles not risking that smart motorway,away on Sunday to Spain so I’ll have a good think on the beech.

Post by **Micron** » Fri Jun 06, 2025 2:57 pm

Have you tried to let it tick over on the drive for a while to see if it cuts out. If it does, then try to restart it, if it does wait 20-30 mins and try again, if it then starts I would say it could be the dizzy?

Post by **Tommyb 2579** » Fri Jun 06, 2025 4:06 pm

I’ve got a new cps ordered so will see if that makes any difference,if not then have a look at dizzy,there’s one in my garage loft but I think it might be a early one,but I’ll wait till back from holiday before I do any more, thanks for the input Trev appreciated.

Post by **Sunfly** » Sat Jun 07, 2025 8:17 am

Two things will cause an otherwise ok engine to not start. CPS circuit and No1 tdc sensor. Can’t remember its proper acronym. When the cps fails it will keep running till you stop it cus it knows from the tdc where the rotation of the engine is, but when stopped it needs the positional info from the cps to get it started then the tdc can take over. If the tdc goes on the blink it can’t run.

The Bosch immobiliser will cause it to stop when running for no apparent reason caused by dry pcb solder joints

A failing dizzy before it finally gives up the ghost will often be a poor starter and will falter or not run smoothly.

No 1 tdc sensing is a function of the dizzy from memory. Mechanically it always knows where tdc no 1 is because it’s connected to the camshaft but the electronics is a different matter.

Such is my experience. Take your pick but if you blame the dizzy you’re rarely wrong. Being intermittent as it is I’d say dizzy most likely Bosch immobiliser highly likely if still fitted but not the cps.

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