Re:Crank no Start on 2005 Mazda B2500TD Diesel

Hi folks
Please could someone help me out?

I have a crank no start on a 2005 Mazda B2500 Diesel. This particular model never made it to North America, so I am looking for general advice rather than super specifics. (although it is very similar to the Mazda BT50 and Ford Ranger)

The problem (or a symptom) is that the PCM does not ground the main relay circuit.
(Very (very) similar to this thread here )

If I take the command side of that relay at the pcm and ground it then the circuit energises and the truck starts and runs well.

From that previous thread this looks like Pauls test 1 - result yes, circuit is powered, relay clicks

For test 2, B+ to relay control at PCM via incandescent test light - no light, no power (measured 0.12v between)

the PCM has 3 powers and 7 grounds,
all the powers provide B+ (within 0.1v)
all the grounds seem fine.

Is the PCM toast or are there other tests I can do?

I assume the immobiliser is not interfering?
thanks
simon

can anyone suggest any further tests before I condemn the PCM.
('always tough to call a computer', right?)

I'm not sure exactly what is required for the relay to be grounded, but general basics, can you communicate with ECM? Does the cel come on with the key in the ignition in accessory position? Do you have 5v at any of the accessable engine sensors? Can you communicate with any other modules?

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Ah, I totally missed that!

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Thanks Guys
I do have wiring diagrams, what should I be looking for? or should I post them here?
The main relay powers the crank sensor, which made me think the pcm should ground that command circuit just with the key on and not depend on any other inputs.
Maybe thats a bad assumption?

The immobiliser light only comes on (in the normal operation way) when I manually ground that command, which makes me think that the immobiliser is not preventing the ground. Maybe thats a bad assumption too?
The immobiliser would prevent cranking if there was a key issue so I assume thats all ok. No comms errors recorded on pcm.

And as I said it runs fine with a manual ground, and cuts out when that is removed.

Thanks for the help

Sorry for the delay getting back I got sidetracked with another car.

Thanks for the suggestions, I will check out the crank signal when I get hold of a helper.

The immobiliser light doesnt even come on if I dont jump the circuit.

I need to check the fuel cut valve power again as that would be controlled by the immobiliser. I thought it was ok, but no sure now..