1996 Volvo D12 wia

Do u have wiring diagram of your truck? plz post me, I have EU D12A diagram, but wire coding differs a bit. I will tell you what to jump and what to check to start ECM

 

Ok, now I can tell u how does this stuff works.

When u turn ignition key it powers pin #6. Processor starts. And after that ECM switches to ground pin #3 to actuate Power relay.

So now pins #11 12 are powered and voltage converter works. Engine may be started.

If ECM throws codes - it surelly works, but if pins #11-12 not powered ore poor ECM grounding (pins 9-10), it throws fault code 14 and wont starting, becouse no power for injectors.

why do they use this silly power supply circuit? Answer is simple - paranoia. If engine selfrevs, ECM disables power relay. And it must stop.

How to check ECM. Things are simple. Put 12V wire on 11 12 and 6 pin and try to start engine.

If it starts - check all feeder relay circut and relay.

Try to jump relay contacts and start engine.

I post u FH12 diagram and fault code list. Very good descriprion how does it work. Pay attention, that europeans use color wire coding, but schematics is the same.

Surelly u will find problem easily

 

I used to fix many D12A ECMs. Usually damages with pressure ore with high voltage, welding, bad wiring

 

did u find feeder relay in cabin?

If yes - jump 30 and 87 terminals and try to start

If engine starts and works, do not forger to remove jumper after u stop engine, becouse powered voltage converter drains battery and heats ECM

 

newer D12B, C D and D13 ECMs are powered by feeder relay but it is controlled by VECU. A bit different approach