dead PCM? or what?

jdc753 · Mar 15, 2013

My buddies truck has been down for a while and he has been attempting to diagnose it as best he can and not getting very far. We keep coming back to a dead PCM but don't want to drop that much coin on a hunch.

What we know:
Truck had a crank but no start condition with a camshaft position sensot pen circuit code

Replaced camshaft position sensor and still nothing

Batteries we're dying with all the cranking and 1 tested bad so he replaced both, and from there things only got worse...

From there the truck would no longer crank from the key. He was able to jump the starter solenoid and get it to crank.

But then noticed the fuel pump wasn't coming on, confirmed no power to the pump, but power to the fuel heater.

With power jumped to the pump the pump comes on and the bowl fills, however truck still does not fire. Cranks and no smoke out the pipe.

He has confirmed power to the pcm and checked all fuses and fusable links, fuel cutoff checks out and ficm checks out.

Also at one point the odometer jumped up to high 200k range when the truck only has 16x on it, it later came back down to close to right reading.

Basically stumped not being able to confirm much and open up more issues as time goes on. So has anyone experienced a faulty PCM.

Mdub707 · Mar 18, 2013

That's odd how it got worse when you put two new batteries in. If that's the case I would suspect some issues with the wires coming directly from the batteries.

The original camshaft position sensor code was probably falsely thrown because of all the cranking. When you could crank it, was it puffing any smoke at all? My guess is not. When you turn the key now can you hear the injectors buzz?

I have a really lengthy thread around here that goes over basically every condition you need to diagnose a no-start as I had a similar issue. Mine ended up being a stuck turbo after all said and done, which still boggles my mind to this day, as I'm still using the same said turbo.

Do you have a scanner to hook up? What's FICM voltage? Is it actually 48V for all three conditions? Do you have SYNC? Do you have FICM SYNC? What's ICP actual/desired and IPR?

Lassie · Mar 18, 2013

If you have a CMP or CKP open circuit code, you will not get SYNC. The cam and ckp performance codes will show during many problems, but the open circuit codes means there is a definite open felt by the PCM. Check your wiring to the sensor with the open code.

jdc753 · Mar 18, 2013

hmm, some good points.

The FICM checks out good, 48.2v while cranking. No smoke while cranking and can't hear injector buzzing.

I know he has chased all the wires, included all chassis wires

Sadly no scanner on hand and I don't know of anyone with AE around. He is hoping to diagnose it and figure it out himself but seems it is getting close to maybe needing to bring it to a shop to actually check things out.

Mdub707 · Mar 19, 2013

What does the FICM read with key on engine off? If you turn the key on and don't hear any injectors buzzing that will at least give us a direction to look.

I should have originally asked this, but what caused it to be put up anyways? You said it's been down for a while, well, why did it originally go down? Die on the road? He shut it off and couldn't restart it???

jdc753 · Mar 19, 2013

FICM checks out with 48v, been tested a couple times since that seemed like the obvious answer.

Originally was an intermittent crank no start condition, somedays it would fire off some it wouldn't. Been down a while since he had another vehicle and not much time to work on it so sort of on the back burner, would get some attention on the weekends and such. Then when he started diving into it that is when things seemed to go downhill, went from a classic simple crank no start (like a bad FICM) to a huge mess it is now.

jdc753 · Mar 19, 2013

Got an update...

The pcm was the the cause of no crank. Still wont start and fuel pump doesn't come on till key forward to start so you have to bump it. Still can't read ecm with the new one

I guess it is progress and he is still looking for an IDS computer or so to hook up to and finally figure things out.

Atsah · Mar 19, 2013

jdc753 said:
Got an update...

The pcm was the the cause of no crank. Still wont start and fuel pump doesn't come on till key forward to start so you have to bump it. Still can't read ecm with the new one

I guess it is progress and he is still looking for an IDS computer or so to hook up to and finally figure things out.

Somthing wrong in the ignition maybe.. :shrug:

Mdub707 · Mar 20, 2013

Definitely need to get this hooked up to something. I'd be looking at SYNC, and FICM SYNC now.

Cold Roller · Mar 20, 2013

He now can't read the PCM (OBDII), won't crank, no fuel pump... It was probably intermittant and now it is full-on broke. Seen this the other day and it was the VRef 5v+ was shorted out due to a wire very near the ICP sensor. Chased down grounds, fuses, relays but it was a simple little wire. There are only a handful of sensors or wires to trace out the problem. Thank Jugernaut.