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Mike, UK Car Mechanic
Category: UK Car
Satisfied Customers: 39198
Experience:  Hi, I am a Car/ vehicle technician of 34 years. 29of -running my own repair/diagnostic business.
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Citroen C3 Desire engine auto-diagnosis light on engine starts

Customer Question

engine auto-diagnosis light on engine starts but no definite drive
Submitted: 5 years ago.
Category: UK Car
Expert:  Mike replied 5 years ago.

Hello and Welcome to justanswer.........


As you have an EML on ..( Engine Management Light ) ( "auto diagnosis light ") this is indicating that the ECU - management computer, has detected and logged a fault or faults, somewhere in the engine management systems...

This could be a sensor fault or wiring issues or even a fault with the main ecu itself... ( the latter is quite rare ) but you see the problem... it's impossible to guess where the fault(s) may be.

What you will need to do now is have the cars systems connected to a suitable diagnostic machine - preferably dealer level equipment... to read / scan the cars ecu - to retrieve the now stored / logged fault code(s)...

Once these are retrieved - then you / the user - will be directed to the area of fault and that can then be dealt with.

To be honest , its usually a sensor fault or a poor connection somewhere... but as I said earlier - it's impossible to guess.

What you can do on a DIY basis - is go around all the wiring connectors around the engine - giving them a tug and a wiggle... just in case you have a poor connection somewhere on one of the sensors / drivers etc... If you do happen to hit on one thats causing the light to come on - the light will usually go off then at the next "start" as the ecu will see the fault is cleared. ( Some cars you need to have the ecu cleared with the diagnostic equipment ) ...

So try that -its worth a try... but failing that - you will need to have it connected up to equipment as I've mentioned...

Many smaller garages have suitable equipment for these these days so if you cannot locate the fault yourself as above - then have a ring around to arrange to have that done and then it will get sorted.

The reason the engine holds back on power by the way - will be because of one of two reasons.... either its because of the actual fault in itself - or, the ecu has put the systems into whats called LHM - Limp Home Mode... this is a basic running mode -(default settings) to allow you to get home (or a garage ) rather than break down -- and this protects the systems - so that you cannot rev it above a certain range whilst the fault exists...

I Sincerely XXXXX XXXXX have helped you - but do ask me if you need anything more..

Kind Rgds, MIKE


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