This weeks Diagnostic Dilemma an Audi Q8 non start

Audi Q8

Recovered to the workshop this week an Audi Q8 reported as a non start no crank vehicle .Initial investigation confirmed the customer description visually there were multiple warning lights and messages on the dash display.

 

 

Audi Q8
non start no crank Q8

After supporting the battery with a support battery charger we set about our vehicle assessment process , initial global scans vehicle scans revealed multiple faults across multiple control units  after saving the vehicle report we cleared all control units to see what would return. Worryingly our visual inspection showed evidence of rodent damage to the under bonnet insulation close to the main engine control unit at the bulkhead.  We had loss of communication with the motor generator ( this vehicle uses a 48 volt system ) it was also reporting a fault with the brake position sensor hence the no crank situation, there was also many low voltage faults across many control units especially the engine control unit showing a power up relay fault.

We decided to concentrate on the power supply to the engine control unit first , after consulting manufacturer’s wiring diagram’s we determined that this supply was via a relay located in the nearside fuse board /relay holder .We initially by passed this relay to see what effect this would have . By passing the relay restored power to the engine control unit and the vehicle would then crank over so we then needed to determine why this relay was not operating . Testing at the relay socket reveled a voltage supply fault to the relay operating coil . Again consulting the manufacturers wiring information we could see that this relay voltage supply  was via a fuse on the same fuse board . Testing the fuse showed that is was intact and had voltage both sides , at the same time we tested all the other fuses in the board and established that with the relay not working the complete top row of fuses were not powered up as these are supplied by the same relay . At this stage we were suspecting possible rodent damage to the wiring loom .

After advising the customer of our findings we were given approval to investigate further , pulling back the fuse board we could see that the wiring ran under the carpet and as the wiring diagram showed a joiner or splice for this supply wire we needed to gain access to this loom to locate the splice . Removing the seat and side trims we were able to get better access to the main loom , there was evidence of water ingress under the carpet and when we traced the wire we found that the splice for this wire was corroded under the insulating tape and had separated inside . After stripping back the wiring to get to some non corroded wire we were able to re join the splice and this restored the relay operation along with power supply to all the other fuses . Clearing and rescanning the vehicle showed no faults and the vehicle would crank and start normally a complete fix with no parts used in the process.  Probably a better conclusion than the potential effect of wiring having been chewed through although quite a mission to get to the wiring loom

 

Rodent damaged insulation
Rodent damaged insulation

 

 

 

 

 

Carpet lifted up

 

 

 

 

corroded wiring splice
corroded wiring splice

 

Corroded wiring to the main power relay

 

 

Our industry standard vehicle assessment provides evidence based results quickly pin pointing the root cause of the vehicles issues saving time and money without having to waste money on unnecessary parts .

 

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