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Greg Szczygiel
Greg Szczygiel, UK Car Mechanic
Category: Car
Satisfied Customers: 12
Experience:  Vehicle technician and electrician currently working in reputable independent garage in UK. Fully acredited ATA diagnostic technician.
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A190 2001 intermittent starting problem. Changed starter motor,

Resolved Question:

A190 2001 intermittent starting problem. Changed starter motor, ignition switch, battery.
Still having problem. Switch on all dash lights come on but turn ignition further to start engine. nothing. This problem has been happening over the past few months, had AA out numerous times, taken to AA approved garage, now in my local garage. They say it might be a relay! Can you advise. Many thanks
Submitted: 2 years ago.
Category: Car
Expert:  Greg Szczygiel replied 2 years ago.
The starter motor is controlled by 2 relays, Engine control module, immobiliser control module and ignition switch.
Relay 1 (Engine control) must supply power to Relay 2 (Starter inhibitor) in order to activate starter motor.
All of the above will not work if Immobiliser is not allowing engine control module to supply voltage to the relays.
I suggest to check starter relay operation while turning key to start position it is located in footwell fuse box.
If relay is not responding the engine control relay must be checked from engine control module (under bonnet relay box).
If relays are checked ok, we may suspect wiring fault or engine control unit with immobiliser.
Another way to approach this type of fault is to use diagnostic equipment to check if signal from the key turned into start position is being detected by engine or immobiliser module and go from there.
I hope it helps.
Greg Szczygiel and other Car Specialists are ready to help you
Customer: replied 2 years ago.


Many thanks info. It looks very possible you are right. Can I come back to you when we have been able to try out your suggestions.

Once again thank you.


Expert:  Greg Szczygiel replied 2 years ago.
, sure no worries, I'm happy to assist you at any point in order to find the answer.
Customer: replied 2 years ago.

Many thanks Greg,

The car is running and seems ok, but as stated ealier it has been an intermittent fault and so we cannot say if the fault has been rectified. The car was running prior to your reply re the relays. We fitted 1 of the relays but could not locate where the other one went. We even spoke Merc main dealer and tried with their suggestions but we still could not find where to put the 2nd relay. The car is running but we wait and see.

Many thanks


Expert:  Greg Szczygiel replied 2 years ago.
, I hope replacement of the relay will fix the problem, Starter relay should be under bonnet in fuse box, second one I've mentioned is in footwell fuse box, it is not starter relay but if it will not work it will also make starter relay inactive.
Hopefully it makes sense.
Let me know how it goes.

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