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Matt, Mechanical Engineer
Category: Audi
Satisfied Customers: 20391
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a audi q7 2007 s line. 3ltr tdi. my car does not start

Customer Question

i have a audi q7 2007 s line. 3ltr tdi. my car does not start at times and i will have to wait an hour or 2 before i try again and it would start. the coil light and the esp traction control lights stay on and it will not start.
on dash it gives a warning message esp fault check owners manual. i have had car checked and was advised to change battery which i have done. all faults went away for 2 weeks.
now the problem has come back again.
Submitted: 5 months ago.
Category: Audi
Customer: replied 5 months ago.
i have also changed the relay underpassenger seat next to battery but still no luck. this happens sometimes.
i have to wait a few hours before i try again and it will start.
Customer: replied 5 months ago.
at times i can hear a ticking sound when i press the brakes. the sound comes from the rear passenger side light
Customer: replied 5 months ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Customer: replied 5 months ago.
no fault codes are showing
Customer: replied 5 months ago.
iv noticed that the gear display is in red now. its normaly in white.
Customer: replied 5 months ago.
its not flashing but sometimes when i start the car the gear display PRNDS is displayed in red
Customer: replied 5 months ago.
Hello anyone
Expert:  Shantal-Mod replied 5 months ago.
I'm Shantal and I'm a moderator for this topic.
I've been working hard to find a Professional to assist you with your question, but sometimes finding the right Professional can take a little longer than expected.
I was checking to see if you had already found your answer or if you still need assistance from one of the Professionals.
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Thank you,
Customer: replied 5 months ago.
Im still waiting for an answer. Hope im not charged for this until its solved
Expert:  Matt replied 5 months ago.


sorry that you've had to wait for an answer, as this issue looks quite complex

I've known an ESP fault to immobilse a car in this same fashion as the traction control is on all the time which limits engine power to such an extant the engine will no longer run

I'm surprised that there are no logged fault codes as this sounds like there may be a transmission fault as well as the ESP issue

However with ABS / ESP systems 99% of the time its a problem with one of the wheel speed sensors and I'd first check the connections at all four corners first for any signs of corrosion or chafed wiring.

The sensor is located in the wheel hub so you'll have to remove each wheel in turn to inspect them all.

Also check that the toothed wheel that the sensor points to is clean and free of any debris.

you can check each sensor's function by plugging the two output wires into an AC voltmeter and spinning the wheel quite quickly, you should get a voltage signal that increases with rev's.

Its possible that the fault is only a bad connection to one of the wheel sensors.

This may be remedied by removing each wheel in turn and unplugging each sensor and cleaning the contacts with a squirt of electrical contact cleaner. Then refitting.

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

Customer: replied 5 months ago.
Have booked in for checkup this monday and will give you update. Thanx
Expert:  Matt replied 5 months ago.

no problem

Customer: replied 5 months ago.
Had it checked and faults showing ecu communication
As follows
Customer: replied 5 months ago.
When coil light and esp light stays on the engine turns but doesnt start.
Iv just replaced the ec relay but still no luck
Expert:  Matt replied 5 months ago.


1st thing to check is if you have 12V on the ECU fuses with the ignition on and check the state of these fuses for corrosion and signs of overheating - also check that the correct rating is in each slot

If thats all OK then I'd suspect that either the ECU is faulty and should be sent off for testing or there's a fault with the CAN bus communication between it and the other car modules and probably down to a corroded connector so I'd check the ECU sockets - spray with contact cleaner and work back from there

Expert:  Matt replied 5 months ago.


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