Truck won't crank

[nonickatall]

I have a problem with my truck. it won't crank.

I had that problem a month ago as well a few times and I swapped the battery, after that it didn't happen again.

Today I helped someone who had a problem with his car. His battery was empty, so I bridged his battery with my battery while my engine was running. I checked the other car for error codes and noticed that my engine was had stopped for whatever reason.

After that i tried to crank, but nothing happens.

I thought first: My battery is low and I put on a charger.

The battery is new and now full and when I turn on the ignition, I have normal lights in my instrument cluster.

When I switch to start, I have the lights going away, like normal.

But there is no crank, so I first removed my right wheel and measured at my starter, if current is available. I can measure ground to ground and I have 12 Volt at the power line, from the battery.

On the line which controls the magnetic switch of the starter, there is no 12 Volt, when I let someone start the truck.

So I looked for the starter relay. I swapped the starter relay with the equal relay next to it, with "park lp", whatever that means. No change.

So I looked for the description on the relay and I measured between 87 an 86, but there is no current, so it seems that something else don't work.

I tried to bridge 30 to 85 but the starter don't crank as well.

When I switch on the ignition. There is this sign with the lock. I'm not sure if that is always there.

Does anybody have an idea, where I can start to search for the problem?

Best regards from Germany
Ralf

 

[Scottydoggs]

the fat cable to the starter should always be 12 v hot. the small wire should show 12 v when the key is turned to crank, its the trigger wire. so if thats got power the starter is not working, if its not getting power it could be something like the starter relay, or the fuse box melted under the relay, or the ignition harness in the steering column has gone bad.

 

[Fless]

Hit this link for an electrical diagram, but you may need to change the link at the top, depending on your specific model. I suspect one of the ignition fuses may have blown, but that's just a guess.

System Diagram — 2006 Cadillac Escalade/ESV 2WD V8-6.0L VIN N Service Manual | Operation CHARM

Detailed repair manual for the 2006 Cadillac Escalade/ESV 2WD V8-6.0L VIN N.

charm.li

 

[rockola1971]

I 2nd an ignition fuse popped. After that I suspect ignition switch on the steering column is burnt at contacts.

 

[Fless]

Also, your owner's manual will have a diagram of the various electrical centers (fuseboxes) with somewhat limited descriptions of each fuse.

 

[nonickatall]

Thank you all very much.

the fat cable to the starter should always be 12 v hot. the small wire should show 12 v when the key is turned to crank, its the trigger wire. so if thats got power the starter is not working, if its not getting power it could be something like the starter relay, or the fuse box melted under the relay, or the ignition harness in the steering column has gone bad.

I have 12v on the main cable of the starter and ground from the ground cable. But on the trigger wire, i have at start no 12v. So that must be the reason for the problem.

As far as i unterstand, these trigger wire comes from the starter relay. I am not sure if something is betweeen, like the key lock system, because when I bridge 30 to 85 on the relay socket, the starter should turn, like i know that from other cars. But it dont.

As well, i have not signal on start on 86 and 87 which means the problem, must be between ingnition switch and key lock and or engine controll unit.

Hit this link for an electrical diagram, but you may need to change the link at the top, depending on your specific model. I suspect one of the ignition fuses may have blown, but that's just a guess.

System Diagram — 2006 Cadillac Escalade/ESV 2WD V8-6.0L VIN N Service Manual | Operation CHARM

Detailed repair manual for the 2006 Cadillac Escalade/ESV 2WD V8-6.0L VIN N.

charm.li

Thank you very much for that info, i will try to check that.

I 2nd an ignition fuse popped. After that I suspect ignition switch on the steering column is burnt at contacts.

I found only two fuses for the ignition on the fuse box diagramm and ckecked both. Both are ok.
Is there a proper way to check the ignition switch? Is that switch available as spare part?

Also, your owner's manual will have a diagram of the various electrical centers (fuseboxes) with somewhat limited descriptions of each fuse.

Yes, ich found only two fuses, i am not sure if there a more.

 

[nonickatall]

Interesting fact is:

When i had the problem first, a few weeks back. The car was driving, i stopped at the school to pick up my daughter and after 5 minutes, i tried to start the engine again. My battery seems to be dead, because there was only a "click" noise from the starter. So i asked another mum to bridge my car. I have allways a starter cable in the truck. That didnt work. There was also only a "click". So i went home and come back later with a charged battery.

Strange was that the car made a alarm noise, like from the key lock system? And my Radio was not going off, when i switched off ignition and opened door like normal.

With the charged battery and after a few hours, i came back, bridged my car and it startet. But Radio was in a strange mode and the instrument cluster was dead. I had not temperature, speed, or engine rotations.
I
I drove home and disconnected the battery for a short time. I charged the battery and connected it again. After that the car startet and instrument cluster and radio was normal again.

I had that behavior another 2 times, then I swapped the battery with a new one. Since then that never happend again until now.

Any ideas?

 

[nonickatall]

I found something. I checked all the fuses an found a blown PCM B 20A fuse. I replaced it and the truck cranked for short. The engine didn't start, but maybe it cranked to short.

The fuse was immediately blown again.

Anybody an idea what to check?

 

[nonickatall]

I ask Chat GPT about that issue and it told me this points.

---

1. Short Circuit in a Sensor or Actuator

The PCM provides power to multiple sensors and actuators via the PCM B fuse. A short circuit in one of these components can overload the fuse. Commonly affected components include:

Throttle Position Sensor (TPS)

Mass Airflow Sensor (MAF)

Crankshaft or Camshaft Position Sensor

Fuel Injectors

Ignition Coils

EGR Valve (Exhaust Gas Recirculation)

Alternator (if internally faulty, it can backfeed power)

How to test:

1. Disconnect the connectors of these components one by one and replace the fuse each time.

2. If the fuse does not blow when a specific component is unplugged, that component may be faulty.

---

2. Problem with the Alternator

The alternator is often connected to the PCM B fuse. If it has an internal short circuit, it can cause the fuse to blow.

How to test:

Disconnect the alternator plug and install a new fuse.

If the fuse does not blow, the alternator might be faulty.

3. Ground Issue or Moisture in the Fuse Box

A bad ground connection or moisture in the underhood fuse box can also cause short circuits.

How to test:

Open the fuse box and check for corrosion or moisture.

Remove all fuses and relays and inspect the contacts for damage.

So I disconnected that small plug from top of the alternator, put in a new PCM B Fuse and tried again.

The fuse did blow again.

Does anybody know how too remove the cover from the PCM?

 

[rockola1971]

I ask Chat GPT about that issue and it told me this points.


So I disconnected that small plug from top of the alternator, put in a new PCM B Fuse and tried again.

The fuse did blow again.

Does anybody know how too remove the cover from the PCM?

Check resistance to ground at both terminals of the PCM B fuse. PCM B fuse also feeds power to some of the PCM so you may need to pull the C connector at the PCM and inspect for the green crusties growing on pins of the plug. Clean with rubbing alcohol and nylon bristle brush (While battery is disconnected).

Ive seen the cluster go haywire and radio not react correctly with a low voltage condition caused by either low alternator output or a battery with one or more dead or very weak cells.

Ignition switch is still available and cheap.

Power flow for ignition control (S terminal of Starter/ Small wire) is Fuse > Ignition Switch > BCM > PCM > Start Relay > S Terminal Starter.

If you know how to work a meter I can pull up your vehicle specific schematics and walk you through electrical checks to see where the voltage is stopped during the engine crank but with a fuse blowing it sounds more like you have a short to ground or crusties on terminals at PCM.

 

[nonickatall]

@rockola1971

I disassembled today the PCM. The connector was absolutely clean, no green crust.

I opened up as well the PCM and as well inside, it looks absolutely clean.

Yes I have a meter and I can work with it, I would appreciate your help very much.

I measured to ground at the fuse socket. On the terminal pointing to the front of the car, I have 90 ohm resistance. The other has no ground.

 

[nonickatall]

I have a friend how has the same truck. Can i swap the PCM, just to check if his PCM works, or do I have to program the Key Lock system or something else?

 

[rockola1971]

Have you done any work lately that involved installing any sheet metal screws or disassembly/removal of anything hard like a valve cover, alternator, master cylinder, etc? If so, thoroughly inspect around the part for a smashed, pinched wire harness. Also look for a wiring harness under the hood that is rubbing up against metal and has wire insulation damaged. If nothing at all those then I suspect your problem is internal of the PCM since a fuse is blowing to it.

 

[rockola1971]

I have a friend how has the same truck. Can i swap the PCM, just to check if his PCM works, or do I have to program the Key Lock system or something else?

You should be able to do a direct PCM swap. The PASSLOCK is in your BCM so no problems there. There may be some accesories like AUTO AC or maybe the radio that may not work correctly or not at all but the vehicle should start with your friends PCM. A BCM is programmed to the PCM but I believe thats only for certain features inside the vehicle to work.

 

[nonickatall]

No i did very less in the last half year on my truck. Only known problem is that my fuel pump is leaking. I smell gasoline when i drive. I have a new pump here, but wasn't able to fix that problem yet. Aside from that, everything worked, an the engine runs good.

 

[nonickatall]

I talked to my buddy and he will come tomorrow with his PCM, so i can check if the PCM is the problem.

Do you think the fuel pump can cause the problem by shortcut, because of the fuel leak?

 

[rockola1971]

I talked to my buddy and he will come tomorrow with his PCM, so i can check if the PCM is the problem.

Do you think the fuel pump can cause the problem by shortcut, because of the fuel leak?

Fuel pump leak (I assume you mean oring at the tank or broken hose connection at the tank) aint causing you to not get 12v at your terminal S at the starter. It also isnt causing PCM B fuse to blow.

 

[rockola1971]

Ok I tracked down some schematics for you 2006 Esky. Igntion E fuse is the feed for the control circuit for your starter RELAY coil. PCM B goes to the PCM. Ignition A is the feed for your ignition switch. First check those fuses (We know the PCM B fuse is blowing) then I would pull that Fuse Block up off its base (After disconnecting battery) and check for the green crusties and other foreign material or rodent damage. You still could have a damaged PCM and/or other problem like the fuseblock but at this point I dont believe your problem is in the ignition circuit including your IGN Switch since PCM B fuse is not related to that circuit.

 

[nonickatall]

I swapped the PCM from the buddy, but as soon when I switch on ignition the PCM B fuse blows.

@rockola1971
I will look on on the information of your last post, later ..

Thank you very much for your help...

 

[nonickatall]

I had checked concerning the fuse box. Looks all normal without moisture or green crust...