S4 Solenoid Or Ecu?

Banana-wagon

Registered User
Hi, my B6 S4 occasionally refuses to start. All the lights come on but nothing at key turn. Eventually after locking and unlocking or waiting it starts and runs no problem.

Related things: It is always a long time, several (1-2) seconds between turning the key and anything happening.
Today it died momentarily twice while driving but then immediately started again.
Occasionally the radio turns itself on and off just after starting.
Having read around I'm thinking solenoid or ECU.
Any thoughts?

Incidentally, she's an old girl with 176,000 on the clock, running on LPG, no timing chain rattle, but a regular oil habit.
 

john777w

Registered User
When you say solenoid I guess you mean starter solenoid......these can stick, but would not cause the engine to die while driving, as the solenoid is only active while cranking the engine
 

Banana-wagon

Registered User
Yes, starter solenoid. I thought that and the momentary cut out was a new phenomenon this morning, I'll see if it does it again.
 

dualmono21

Well-Known Member
VCDS Map User
left the passenger side carpet up and see if its damp
the comfort control module is located under there and can suffer with water ingress which can cause all the problems mentioned
 

Banana-wagon

Registered User
left the passenger side carpet up and see if its damp
the comfort control module is located under there and can suffer with water ingress which can cause all the problems mentioned

That is interesting, because a while ago my passenger said that some water had dripped on her feet in the footwell, I presumed it might be from the aircon. I'll look when I get back after the weekend. If it is, what do I do about it other than dry it out? Cheers
 

john777w

Registered User
There are some drain holes under the battery area, if these block, water will overflow into the footwell.
 

rjm180

Registered User
I experienced this and I had water ingress on the passenger side.
 

rjm180

Registered User
left the passenger side carpet up and see if its damp
the comfort control module is located under there and can suffer with water ingress which can cause all the problems mentioned

+1 for what dualmono said.
 

dualmono21

Well-Known Member
VCDS Map User
if it is water logged the best thing to do is remove the passenger seat
lift the carpet and let the ccm module dry of its own accord
if you pop the top off and can see lots of corrosion around the connections it may well have completely done the ccm module
however if you cannot see any corrosion maybe just evidence of water ingress simply open the car door , dry things as much as you can and then let nature do the rest

while this is happening its a good idea to remove your battery and check all the drainage holes underneath it
make sure they are completely clear before re-installing the battery
whilst the battery is out i would also reccomend checking your ecu seal

this is on the drivers side right underneath where the windscreen wipers are
the ecu box has two seperate seals one to seal the box to the bodywork and one to seal the ecu itself
the ecu and housing should be firmly mounted underneath the windscreen wiper this could be where the water is getting in and causing problems
if its not firmly mounted you need to ensure its is and sealed correctly
unfortunatly in the cars past it may have come across a gung ho owner or mechanic who didnt remove all the torques screws to remove the housing and simply broke the last one off
i have seen a lot of these with broken ecu housings
 

S3 GAZ

Registered User
Had very similar problem with my 1.9tdi quattro. Would get intermittent starting problems. Car would crank but not start. Vag com could not communicate with ECU when this happened so pointed to ECU. When I opened up the ECU box I found ECU power relays sitting in pool of water. Wiring was to relay was corroded.

Replaced ECU power relay and fixed wiring and. Drilled a couple of holes in ECU box and used some sealant on the lid.

Never had any issues after that.

As mentioned above I had to remove window wipers and scuttle trim to get to back bolt on ECU cover. Don't brake it or u won't get a seal.
 
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GeoffDunk

Registered User
Hi, my B6 S4 occasionally refuses to start. All the lights come on but nothing at key turn. Eventually after locking and unlocking or waiting it starts and runs no problem.

Related things: It is always a long time, several (1-2) seconds between turning the key and anything happening.
Today it died momentarily twice while driving but then immediately started again.
Occasionally the radio turns itself on and off just after starting.
Having read around I'm thinking solenoid or ECU.
Any thoughts?

Incidentally, she's an old girl with 176,000 on the clock, running on LPG, no timing chain rattle, but a regular oil habit.

I had exactly the same scenario with my B6 S4 and it was the starter solenoid, I posted the problem on here over a year ago and it turned out to be the case after some ideas and recommendations from some helpfull folks; it was my very 1st post.

I initially thought it was the emobiliser, or the key fob but after eliminating that it was just the solenoid, I swapped the starter for new and its never done it since.
 

DanV8

Still waiting for a new ECU!!
Thats what killed my ecu and voltage relay as some idiot had removed them in the past (before my owner ship) not sealed them back correctly and water was inside killing both units, £1700 and 6 weeks later, all sorted!
 
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