Intermittent fail to start
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Intermittent fail to start
2013 Q5 3.0T, 115k miles. Maybe 1 in 20 times, it will fail to start. Engine cranks fine, everything appears normal, just no fire up. Once it does start, it runs 100% fine, no issues at all, no codes, warning lights etc. Has new battery and spark plugs. It will either fire right up perfectly, or literally refuse to start. You can crank until the battery is dead and it would not start. I have not been able to trace it to anything in particular, but if you lock the car and try again later, it often works.
Some (potentially relevant) information. We had a water pump failure and coolant sprayed everywhere. The issue appeared after that. Maybe just coincidence, but wanted to mention. I know it has to be the usual air/fuel/spark diagnosis. Given it runs fine when running, and 95% of the time it fires right up, I have mostly dismissed more obscure issues that should be always present. My guess would be electrical - either immobilizer (there is literally no sign of a spark when the issue occurs), or potentially a relay not kicking in the fuel pump or something similar.
Before I start chasing ghosts, I thought I'd share here and see if others had ideas. (yes, I did search, but other posts were mostly no crank, or difficult starting. This is not difficult or rough starting. It either fires right up perfectly, or will refuse to start).
db
Some (potentially relevant) information. We had a water pump failure and coolant sprayed everywhere. The issue appeared after that. Maybe just coincidence, but wanted to mention. I know it has to be the usual air/fuel/spark diagnosis. Given it runs fine when running, and 95% of the time it fires right up, I have mostly dismissed more obscure issues that should be always present. My guess would be electrical - either immobilizer (there is literally no sign of a spark when the issue occurs), or potentially a relay not kicking in the fuel pump or something similar.
Before I start chasing ghosts, I thought I'd share here and see if others had ideas. (yes, I did search, but other posts were mostly no crank, or difficult starting. This is not difficult or rough starting. It either fires right up perfectly, or will refuse to start).
db
AudiWorld Senior Member
Joined: Nov 2023
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From: Sweden
Before asking questions about modern cars, it is crucial to first read the error codes. These codes can often provide valuable insights into the issue and may even resolve the problem without further assistance.
AudiWorld Senior Member
Joined: Feb 2018
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From: Canada
Is the issue temperature related? Meaning does it only happen when engine is hot or when cold?
Check the Crank Position Sensor. Try using VCDS or similar tool to log the CPS when cranking while it is not starting. If it reads zero rpm while cranking then CPS has likely become intermittent and will eventually fail completely.
Check the Crank Position Sensor. Try using VCDS or similar tool to log the CPS when cranking while it is not starting. If it reads zero rpm while cranking then CPS has likely become intermittent and will eventually fail completely.
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superman22x
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Feb 26, 2024 07:40 AM
