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Robert, UK Qualified Car Technician
Category: Car
Satisfied Customers: 4709
Experience:  Fully qualified / self employed garage technician in the UK
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Interchange jumper cables while jumpstarting a merc A140,

Customer Question

Interchange jumper cables while jumpstarting a merc A140, now car just cranks but wont start? advice? have i burnt some fuses? is the ECU damaged?

Submitted: 3 years ago.
Category: Car
Expert:  Robert replied 3 years ago.


Hopefully i can help..

Normally you do actually blow the main/heavy duty fuses first if you have crossed the jump leads - those are the larger ones often in the main fuse box normally just the two so certainly check them first - on the A-class it should next to the main battery -

Customer: replied 3 years ago.

Thank you for answering my question. Would they stop the car from starting? If they are the ones that are blown? In this case the battery was completely flat? could this also be a reason why its not starting? Just going to check the huge fuses. Thanks

Customer: replied 3 years ago.

Checked all fuses next to the cables and all seem to be in good nick, what else can you suggest i do?

Expert:  Robert replied 3 years ago.

Hi..apologies for the delay..lost internet connection..

You need to be sure the fuses havent blown..pull them out and check the centre strip is intact..normally the large rated fuses do protect the systems for damage if its jumped the wrong way would also be worth double checking the smaller ones on that fuse panel too..other than that it possible the ecu/controls units have suffered a voltage spike - normally that would have to be tested for diagnostically/car plugged in so to speak before jumping straight in with replacement of those..but like i say you need to fully 100% sure that all fuses/inc those larger amp rated ones are intact..if so and alls ok then im afraid there might be possible damage elsewhere/immobiliser issue has surfaced only way to know is to get it scanned..maybe try disconnecting the battery..take both leads off and away from the battery posts itself and touch them together for about 10-15min then put the leads back on the battery and then see if that helps...