My volvo mechanic can't figure out what is wrong with the car and I have posted to other volvo forums. It used to be intermittent, but basically the car does not crank. All the dummy lights come on and everything else works. I have changed the following items:

I initially replaced the starter
Ignition Switch
PNP Switch
Terminal connections were checked
Replaced positive battery cable
Brand new battery
Electrical connectors on the wiring harness on the starter motor

They did mention that bypassing the ignition to the starter works.

The other thing that is interesting is if the car does not crank, if the car is jumped, for some reason it will start up. I mentioned this new information to my mechanic and it did not help him with any diagnosis.

Anyone have any thoughts?

 

well, when you get a jump start, you're getting 14Vs from the running car not the 12.6V from the battery (assume your new battery will measure out as charged). Have you put a meter on the battery terminals to see where the voltage goes to when you turn the key? See if volvotips.com has anything useful posted for the anti-theft system. I'm wondering if the immobilizer is causing the no-start...

 

I tried all the tricks with the immobilizer:
Disconnected the battery
Pressed the alarm and then locked/unlocked doors several times

Not sure what else to do.

 

Immobilizer would not be disabled by jumping the car. Someone should look at it who knows how to do voltage drop testing on the high current battery cables while trying to crank the engine. Trying to crank engine w/remote starter switch would tell you a lot too.

See you replaced the positive cable, but what about the negative? Starter will draw around 100A IIRC; it's got to go through both cables you know..

But wait, what does this mean? "They did mention that bypassing the ignition to the starter works."

 

I bought a Hulkman Alpha 85 portable jump starter with 2000 Amps to start the car and nothing happened. I decided to jump start the car using my other car and it started right up. Does this make any sense as to what is going on?

 

No, it doesn't. Unless you jumped them differently.

When you jump started your car with another car and jumper cables, where did you hook up the negative jumper cable on the 850 (jumpee); to the negative battery terminal, or the engine block?

 

Both times to the negative battery post.

 

Will it run if you just trigger the starter with a wire? Is that what I am understanding from your first post?

 

Yes, that is correct.

 

has the car run since you installed the PNP switch or did you do all those changes (ie ignition switch, PNP) trying to get it to start?

 

Yes, I have done all those changes trying to get the car to start up consistently. The no start condition has been intermittent. It was guaranteed to start up every morning and can drive it, but if you went to make multiple stops, the car would go back to a no start situation. Eventually it would start up again.

 

Here's a wiring diagram focusing on the immobilizer. The transmission safety switch looks like a relay here (to me) but it's the switch at 3/71


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I suppose the "right" thing do to would be to see if you have power at this switch and whether it comes on during "start" (need 2 people to do that). That'll tell you if the immobilizer is involved and if the transmission switch is turning on and off. If the immobilizer is involved, then I don't know what you can do about that. Over my head.

 

The mechanic installed a new PNP switch. Are you saying it might not be getting power from something else? I have no clue how to test it though. Not a DIY guy.

 

Well, print that wiring diagram and give it to him.