Engine cut out, wouldn't restart - solved

[T!M]

I had a squeak coming from my accessory belt so decided to take it off and check all the pulleys.
There was minimal end float, no graunching and very little play on the pulleys for the tensioner, idler or the power steering and air con pumps. The alternator clucthed pulley operated correctly and the serpentine belt was in good condition so I refitted it.
Started the car, squeak gone, I think the tensioner mechanism may have been a bit grubby and sticking then was freed up when I excersised it, result!


Two minutes later the engine cuts out with the ESP warning showing on the DIS.
Re-started, two minutes later same again but I noticed the rev counter instantly dropped like a stone (loss of power/ signal?).
Re-started engine again, ran fine for 10 miles then fault re-occured.
Plugged in a cheapo code reader, no logged DTCs.


The car ran fine for a couple of days then cuts out again and all hell breaks loose with the warning lights & DIS.
ECS (engine management light, ESP, Glow plugs and red oil low pressure when the engine cut out.


I was a bit worried about the oil low pressure but decided it was a symptom of the fault and if it re-occured on restart I'd just shut down immedeately. The engine cranked healthly but wouldn't restart and the DIS showed ECS, ESP, glow plug and brake fault warnings, again no DTCs logged.


The radiator cooling fan sporadically turned on and there was a buzzing & clicking noise from around the EGR valve body area.


My reason for posting this is that I spent a good few hours scanning the forums for causes and eventually found the solution and thought I'd do my bit by collating what I found. Hopefully there's some helpful, cash saving info here for anyone in the same predicament.


Possible causes posted by others with similar symptoms.


Faulty wiring to these sensors or the sensor itself:-
Coolant temp sensor G62
Coolant temp sensor radiator outlet G83
Throttle position sensors G79 & G185
Crank positon sensor G40
Engine speed sensor G28
Brake light switch.


Low battery voltage or faulty battery - checked my static voltage 12.5v (I didn't have an alternator warning prior to breakdown)


Loose connectors or damaged wiring to the injectors.
Fuse #28 - fuel pump
Fuse #43 - Engine managment


Water in the ECU compartment caused by a poorly fitted cover, perished/ damaged cover seal or knackered loom grommet.
This can also lead to water in the drivers footwell.
(The ECU cover screw below the wiper arm is a bugger to get in and out and was missing on mine.)


Faulty relays in the ECU compartment or the wiring to them:-
J179 Relay 457 - Glow plug relay (the expensive one)
J317 Relay 644 (was a 614 before uprating) - Terminal 30 voltage supply for ECU, also supplies V157 Intake manifold flap motor, Glow plug control unit and J293 Radiator fan control unit.
J17 Relay 646 (was 395) - I think this is the low pressure fuel pump


Armed with a checklist I started on some fault diagnosis.


I checked all the listed sensors I could find easily and wiggled the wires to them - no joy.
Removed the ECU, then the relays and fuses in the ECU compartment - fuses ok, relays bell out de-energised, good relay coil resistance figures. Disconnected the bulkhead connectors at the back of the ECU compartment and checked for damaged, corroded or pushed back pins - all fine.


Charged the battery, cleaned the battery terminals/ clamps.
Disconnected, cleaned and secured the battery earth lead to the chassis and resistance tested earth.
Engine still cranked but wouldn't start.


Thought about disconnecting the fuel filter to check for fuel flow but diesel stinks so I didn't bother.


Sat scratching my head when a friend turns up and says a pal has just bought a Launch X431 pro diagnostic tool!!!
Got him round, plugged it in, Launch can't access the ECU automatically.
Got it reading the ECU through a different menu and he says to me "your radio works but everything else is f***ed"!
Every system had an error, he thinks ECU is knackered, I want a cheaper solution so assume the ECU's not powered up.
We borrow some relays from his ex-wifes A4 and substitue them one by one and it tries to fire up with J317 replaced.
Put some battery jump leads on and it fires up and purrs like only a BRE and an Iron Fairy can. I'm happy now!
I put my relay back in and it starts, then it won't - back to the original fault.
Turns out that the female spade connections in the relay holder are splayed out, so not a good connection.
Somone had obviously been poking about in there before as I had the uprated 644 and 646 relays.


I think the battery is fairly old as it had a VW part number and probably installed at an Audi dealership, although it was showing a reasonable voltage and took a charge it just got to a point where it couldn't produce the current required to power everything up and overcome the resitance in the terminal 30 power supply relay coil circuit to operate it.
With the engine running I had 14.5v at the battery so the alternator is fine, but the knackered battery was stealing all the power so the relay kept dropping out dumping the ECU and killing the engine.
I've got a Bosch S5 coming tomorrow and hope that's the end of this particular Audi induced headache.

[Rob69]

Good write up and diagnosis, I like the borrowed relays off the ex-wife!

[T!M]

Cheers Rob,
unfortunately that hasn't been the end of my woes!!
Fitted the new battery and the beast started and ran fine for a few days then cut out on me again.
Launch connected to the ECU but there were no DTC's logged.
I haven't got access to a decent set of wiring diagrams to fault find with so thought I'd start replacing cheap bits.
I started with the J317 and J17 relays as J317 had a scoorch mark on it and the casing was cracked on J17.
Next was the coolant temperature sensor - bit of a pig to get to inbetween the rear of the block and the bulkhead.
Brake light switch didn't cure it either.
The next time it cut out the fault went from being intermittant to permanent.
Symptoms are:-
cranks but won't start
engine management light and glow plug light not lit
ESP and ABS lights lit
Launch can't communicate with the ECU
If I crank it for more than 5 seconds the red brake warning comes up on the DIS.
When the ignition is left in the on position for more than ten seconds the fan turns on.

Now I'm thinking it may be the crank sensor but that's more than a couple of quid and few hours work to change so I want to do some more diagnosis first. I've read that it should read between 500 and 800 ohms across pins 2 & 3 but the sensor connector is hard enough to get to, let alone getting test probes on it.
It would be easier to test it at the ECU connector if I knew what pins it's on.

Does anyone have wiring diagrams for an A4 2.0 TDI B7 BRE?
I want to test the wiring for the crank sensor, brake light switch, coolant temp sensor and ECU power supplies/ earths.

Any constructive input appreciated.

[derk137]

Cheers Rob,
unfortunately that hasn't been the end of my woes!!
Fitted the new battery and the beast started and ran fine for a few days then cut out on me again.
Launch connected to the ECU but there were no DTC's logged.
I haven't got access to a decent set of wiring diagrams to fault find with so thought I'd start replacing cheap bits.
I started with the J317 and J17 relays as J317 had a scoorch mark on it and the casing was cracked on J17.
Next was the coolant temperature sensor - bit of a pig to get to inbetween the rear of the block and the bulkhead.
Brake light switch didn't cure it either.
The next time it cut out the fault went from being intermittant to permanent.
Symptoms are:-
cranks but won't start
engine management light and glow plug light not lit
ESP and ABS lights lit
Launch can't communicate with the ECU
If I crank it for more than 5 seconds the red brake warning comes up on the DIS.
When the ignition is left in the on position for more than ten seconds the fan turns on.

Now I'm thinking it may be the crank sensor but that's more than a couple of quid and few hours work to change so I want to do some more diagnosis first. I've read that it should read between 500 and 800 ohms across pins 2 & 3 but the sensor connector is hard enough to get to, let alone getting test probes on it.
It would be easier to test it at the ECU connector if I knew what pins it's on.

Does anyone have wiring diagrams for an A4 2.0 TDI B7 BRE?
I want to test the wiring for the crank sensor, brake light switch, coolant temp sensor and ECU power supplies/ earths.

Any constructive input appreciated.

Hi. I know it has been a few years since this post, but did you ever solve the problem?

I have the A6 2.0tdi Bre engine and have had the same issues. Currently have a crank no start problem.

[T!M]

Evening Dirk,
Yeah, it was the connections on the J317 relay located in the ECU compartment.
I think someone had been messing around in there before I owned the car.
You can do away with the relay holder and just crimp new female spade crimps on then strap the relay to the housing.
Electrically check the relay first though, there’s a schematic drawn on it.
Unfortunately for me it had also damaged the power board in the ECU and another chip but I got it repaired by a company called BBA Reman which was a hell of a lot cheaper than getting a new one and comes with a lifetime guarantee!
Hope this helps, good luck
Btw mines still going strong at 140,000 miles and no re-occurrence