No Crank BKD diesel engine on a Golf 2004 Mk5

[shabazmo]

Doing this for a local charity so any help appreciated. Supplied 12v to the starter solenoid with the ign on and the car springs into life and drives. My first thought was the ign switch, so replaced that but no fix. The starter relay in the engine compartment has continuity from pin 87 to the starter plug. Pin 30 has 12v with ign on, so my thoughts were that the relay was faulty. I have tested the relay and proven that the contacts close on energising the relay. There is no voltage reading on relay pin slots 85 86 or D. My thoughts therefore are that the supply voltage to energise the relay is missing.

Looking at the current flow diagram, pin 86 is fed from pin A11 of the power supply control unit. I have no idea what or where this is. 85 is to earth and I have tested that the pin socket is a good earth. D pin appears irrelevant as it only receives a signal once the relay is activated.

So how do I get find the fault which allows me 12v power to pin 86 of the Starter relay when I turn the ignition switch to start.

Thanks in advance.

[Crasher]

Remind me tomorrow as I can’t read the current flow diagram at home.

[shabazmo]

Thanks Mate. Will do.

[Crasher]

If you bridge the J682 position sockets 1 and 2 (corresponding to 30 and 87 respectively), does the starter crank? Socket 4 is the earth, 86 is the relay trigger from the BCM and D is the line 50 feedback.

[Roverfan]

Starter operation can be dependent upon the clutch switch

[Crasher]

They don't have that stupid idea on them that early, really annoys me. Another thing, why on an automatic do you have to put your foot on the brake to start the engine even though it is locked in park?

[shabazmo]

Thanks Crasher. Yes, the car does start when you bridge 30 and 87, and yes it does not have a clutch switch.

[Crasher]

It does have a clutch switch but it does not interfere with the starting unless you code it in. So, now you need to see why the BCM is not operating the relay, a faulty BCM is not unheard of but studying the measuring blocks from the steering column controller will help.

[Roverfan]

They don't have that stupid idea on them that early, really annoys me. Another thing, why on an automatic do you have to put your foot on the brake to start the engine even though it is locked in park?

I should be one of those that sees the safety of the design. I once posted a dodgy handbraked parked in gear corsa into the lamp post in front of it...luckily I was into body repair those days

On the automatics I have theorised (probably way off) that it depends on the key design, if they are metal key they need pressing on the brakes, and the mercs with plastic key do not. Is it a choice of key locked in ignition till box in park or depress brake on start up? I drive sprinters and occasionally iveco automatics for my supermarket food delivery job. The ivecos need brake pressing to start. The mercs can be started whilst just turning the key but will not release the key till box is in park.

[shabazmo]

It does have a clutch switch but it does not interfere with the starting unless you code it in. So, now you need to see why the BCM is not operating the relay, a faulty BCM is not unheard of but studying the measuring blocks from the steering column controller will help.

I am not sure what module the steering column controller is but on VCDS there is module 44 steering assist. On that module, terminal 30 voltage is 12v and it states relay voltage is 12v. Also in module 9 Central Electrics which I believe is called BCM, I can see that the line 50 relay is off and when I turn the ignition to start, it changes to on.

I have also back probed the steering control unit output terminal A18 which should be the line 50 supply out. It shows that there is 12v when the key is turned to start.

Can I assume that the Steering control unit is good and focus on the power supply unit or BCM as you have mentioned.
Sorry, if I am a bit unclear.

Thanks