Ecu main relay

[Ciajis]

Hi,

Every now and then the car won't start. When it fails to start the eml light doesn't lit up with the ignition. Posibly no power is coming to the ecu. I checked the ecu and it's clean and dry, can anyone help me to locate main relay, as that could potentially be the problem. I was hoping it will be next to the ecu, but can't see it. Any other suggestions appreciated. TA

 

[WOMBLERULZ]

Check underneath the ecu


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[Charlie Farley]

Hi,

Every now and then the car won't start. When it fails to start the eml light doesn't lit up with the ignition. Posibly no power is coming to the ecu. I checked the ecu and it's clean and dry, can anyone help me to locate main relay, as that could potentially be the problem. I was hoping it will be next to the ecu, but can't see it. Any other suggestions appreciated. TA

normally a failing relay under the ecu module, green in colour, best replace both as there are 2 and check the fuses to be sure but its most likely the relay failing and its a known problem.

you need to lift the ecu module out of the way to access the fuses and relay holder underneath.

 

[Charlie Farley]

here.

 

[kevin elliott]

Just found my ecu box flooded as the last muppet who worked on it left the lid off/lost it which flooded the ecu box in all the recent rain but also let water into the cabin so I had 4" of water in driver side rear footwell and 3" in driver front footwell!!

Ive dried out the ecu box and took the 4 relays out (644 which was new, 614 which was new and 2 smaller black ones same size on the right). Took all 4 relays out and covers off and dried them out - they looked ok, no corrosion etc. Car is drying out now but im worried that other components under the dash have been affected?

Car wont start - it turns over fine but the EML is on and the ABS light too. Any ideas on what to check next please?

 

[Charlie Farley]

Just resolved the same issue with my S4, try spraying some electrical contact cleaner in everything just to help things, if the ecu box itself was wet then you may have bigger issues, normal it doesn’t get soaked as it is higher than the aperture that goes into the driver footwell and water overflows into there and soaks all the wiring within the water range.

 

[Charlie Farley]

Try leaving the ecu box in a warm place for a day to slowly dry out a bit, may help a bit but you will probably need vcds to clear all the faults aswell.

 

[kevin elliott]

Just resolved the same issue with my S4, try spraying some electrical contact cleaner in everything just to help things, if the ecu box itself was wet then you may have bigger issues, normal it doesn’t get soaked as it is higher than the aperture that goes into the driver footwell and water overflows into there and soaks all the wiring within the water range.

Yeah there was water in the ecu box up to the bottom of the relays - took them all out and dried, sprayed wd40 contact spray all over. Ecu itself didnt look to get wet, I do have another one to replace it as I had an intermittent fault before where all the drive lights lit up so it wouldnt fire. Clearing codes with a cheap code reader usually cleared the lights and it started. Not seen EML and ABS lights before though.

Once it starts I can get it to a garage to get the codes out of the old ECU to swap it over to new one. I did have VCDS on it ages ago and it reported ECU intermittent comms and someone before had been in there, cut off side of ecu cover and also had tried to pry ecu case apart??

Will take out the ecu and put in airing cupboard as ive cut slots in the security screws now to get the harness off.

cheers for your quick response!

 

[Charlie Farley]

when those relays in the ecu box get soaked you will get a heap of fault codes across numerous modules, my s4 had 28 faults that were resolved as soon as I replaced the relays and dried it all out.
possibly some of the lower items may have been soaked as the water flowed out of the ecu box and into the cabin.
VCDS is allways the best option.

 

[kevin elliott]

when those relays in the ecu box get soaked you will get a heap of fault codes across numerous modules, my s4 had 28 faults that were resolved as soon as I replaced the relays and dried it all out.
possibly some of the lower items may have been soaked as the water flowed out of the ecu box and into the cabin.
VCDS is allways the best option.

Yeah VCDS is great - I did have a version but got rid of it ages ago. I just took the battery leads off and held them for 10 seconds then plugged in the battery again and it fired up! At least now I can get it to the garage to swap the ecu over - result