Strange No-Start Issue

[e46IX]

Having a strange no-start issue on my M3 that I'm having trouble figuring out. This all started when I had to boost another car on the driveway with a weak battery and the M3 was the only car beside it. I boosted that car, everything was good, I shut off the M3 and next time I went to fire up the M3 all I get is the starter click. Also before anyone suggests it, no I didn't cross-jump the terminals.

Here's what I can tell you:

-The M3 does fire up when I bump start it... meaning I get a rolling start in gear, pop the clutch and it will fire up. Ok cool... gotta be either a starter or bad ground right? Nope.

-Battery is brand new from dealer, and registered

-Engine ground strap is brand new, and I checked all the ground points in the engine bay, getting 11V everywhere and getting power to the positive battery terminal.

-I had a hard time believing a car with only 40,000 km's would have a starter failure so soon but I removed the original starter assembly regardless and took it to a local starter/alternator rebuilder. He said everything was good with the starter but we refurbished it anyways. Before I left, I had him bench-test the starter and sure enough it fires up like new on a bench with 12V hitting it.

-I don't think its the CAS, if it was an immobilizer issue I wouldn't even hear the starter click.

-I don't think it's an issue with corrosion on the positive battery cable that goes from the battery in the back to the front jumper terminal. Car is mint, its not a rustbucket.

-I checked any fuses in the fuse box that made sense to check. I'm getting continuity on all of them.

Scanning with Bimmergeeks ProTool, the only codes I'm getting is from the CAS for:

A0B4 - 'Engine Start, Starter Operation'
A0C1 - 'Output, Terminal 50'

I'm stumped at this point. Any ideas?

[happydude]

Originally Posted by e46IX

Having a strange no-start issue on my M3 that I'm having trouble figuring out. This all started when I had to boost another car on the driveway with a weak battery and the M3 was the only car beside it. I boosted that car, everything was good, I shut off the M3 and next time I went to fire up the M3 all I get is the starter click. Also before anyone suggests it, no I didn't cross-jump the terminals.

Here's what I can tell you:

-The M3 does fire up when I bump start it... meaning I get a rolling start in gear, pop the clutch and it will fire up. Ok cool... gotta be either a starter or bad ground right? Nope.

-Battery is brand new from dealer, and registered

-Engine ground strap is brand new, and I checked all the ground points in the engine bay, getting 11V everywhere and getting power to the positive battery terminal.

-I had a hard time believing a car with only 40,000 km's would have a starter failure so soon but I removed the original starter assembly regardless and took it to a local starter/alternator rebuilder. He said everything was good with the starter but we refurbished it anyways. Before I left, I had him bench-test the starter and sure enough it fires up like new on a bench with 12V hitting it.

-I don't think its the CAS, if it was an immobilizer issue I wouldn't even hear the starter click.

-I don't think it's an issue with corrosion on the positive battery cable that goes from the battery in the back to the front jumper terminal. Car is mint, its not a rustbucket.

-I checked any fuses in the fuse box that made sense to check. I'm getting continuity on all of them.

Scanning with Bimmergeeks ProTool, the only codes I'm getting is from the CAS for:

A0B4 - 'Engine Start, Starter Operation'
A0C1 - 'Output, Terminal 50'

I'm stumped at this point. Any ideas?

Had this issue. Got same codes. I replaced the starter almost 4 years ago and have not had any issues since.

The click you hear is the gear in the starter popping out to engage the flywheel, but the starter was unable to turn the flywheel. Had the old starter bench tested after I replaced it and it worked (spinning with no resistance) and so I concluded it was the starter just being worn out and unable to turn the flywheel to start the car.

[sparayno1]

I had the same codes and replaced the starter to fix the issue. Technically the solenoid was bad, but might as well replace the whole thing while you're there. I made a video guide on how to replace the starter here:

[dpaul]

Originally Posted by e46IX

Having a strange no-start issue on my M3 that I'm having trouble figuring out. This all started when I had to boost another car on the driveway with a weak battery and the M3 was the only car beside it. I boosted that car, everything was good, I shut off the M3 and next time I went to fire up the M3 all I get is the starter click. Also before anyone suggests it, no I didn't cross-jump the terminals.

Here's what I can tell you:

-The M3 does fire up when I bump start it... meaning I get a rolling start in gear, pop the clutch and it will fire up. Ok cool... gotta be either a starter or bad ground right? Nope.

-Battery is brand new from dealer, and registered

-Engine ground strap is brand new, and I checked all the ground points in the engine bay, getting 11V everywhere and getting power to the positive battery terminal.

-I had a hard time believing a car with only 40,000 km's would have a starter failure so soon but I removed the original starter assembly regardless and took it to a local starter/alternator rebuilder. He said everything was good with the starter but we refurbished it anyways. Before I left, I had him bench-test the starter and sure enough it fires up like new on a bench with 12V hitting it.

-I don't think its the CAS, if it was an immobilizer issue I wouldn't even hear the starter click.

-I don't think it's an issue with corrosion on the positive battery cable that goes from the battery in the back to the front jumper terminal. Car is mint, its not a rustbucket.

-I checked any fuses in the fuse box that made sense to check. I'm getting continuity on all of them.

Scanning with Bimmergeeks ProTool, the only codes I'm getting is from the CAS for:

A0B4 - 'Engine Start, Starter Operation'
A0C1 - 'Output, Terminal 50'

I'm stumped at this point. Any ideas?

A0C1 means that Terminal 50 is not being raised to 12 volts to activate the starter solenoid. This is a most likely a CAS problem as there is no relay - Terminal 50 voltage is semiconductor switched inside the CAS module. A0B4 just means you pressed the start button but the engine didn't start.

I don't know what the click you heard was but I'd make very sure where it was coming from. With an A0C1 code, it may be a relay in the JBE or DME box and not the solenoid/starter.

That said, the other concerning thing you report is the value of "11 volts", even with a brand new battery. If you are really only seeing 11v at the battery jumper terminal in the engine compartment, then you should re-examine your assumption that the cable from battery and/or ground straps are good.

Start by putting your voltmeter directly across the battery, then measure from the engine compartment jumper point. If you see 12.3-12.6 at the battery but 11-something elsewhere, a cable or passthrough is likely your problem.

[e46IX]

Originally Posted by dpaul

A0C1 means that Terminal 50 is not being raised to 12 volts to activate the starter solenoid. This is a most likely a CAS problem as there is no relay - Terminal 50 voltage is semiconductor switched inside the CAS module. A0B4 just means you pressed the start button but the engine didn't start.

I don't know what the click you heard was but I'd make very sure where it was coming from. With an A0C1 code, it may be a relay in the JBE or DME box and not the solenoid/starter.

That said, the other concerning thing you report is the value of "11 volts", even with a brand new battery. If you are really only seeing 11v at the battery jumper terminal in the engine compartment, then you should re-examine your assumption that the cable from battery and/or ground straps are good.

Start by putting your voltmeter directly across the battery, then measure from the engine compartment jumper point. If you see 12.3-12.6 at the battery but 11-something elsewhere, a cable or passthrough is likely your problem.

Thank you for the info. Yes don't mind the 11V part, I worked down the battery from trying to start it so many times. I have since hooked up a trickle to it and it's back over 12V.

I have tested voltage directly from battery and at the positive jumper point in the engine bay. There is no loss of voltage between the two points, which leads me to believe the long power cable from back to front is ok.

I will try to get a friend to cycle the ignition while I listen to where the click is coming from, will also check for voltage at the plug that connects to the starter solenoid. I assume it only sends voltage to the solenoid when you actually attempt to start the car, and not just in ignition mode.

In regards to the CAS, if it was faulty do you think I would still be able to bump start it?

[dpaul]

Originally Posted by e46IX

I will try to get a friend to cycle the ignition while I listen to where the click is coming from, will also check for voltage at the plug that connects to the starter solenoid. I assume it only sends voltage to the solenoid when you actually attempt to start the car, and not just in ignition mode.

That's correct - there will only be 12 volts on that line when you attempt to start.

You can also monitor it directly in INPA if you wish. I suppose that a short in the solenoid would pull down the Terminal 50 voltage to a level that would throw the fault. But you already know that the solenoid is good because you tested it on the bench. That doesn't leave much besides a wiring/connector fault or a CAS fault

Originally Posted by e46IX

In regards to the CAS, if it was faulty do you think I would still be able to bump start it?

I expect so but don't know it for a fact

[nrubenstein]

Dead CAS means that the car is absolutely dead to the world. It's very similar to no battery. I'm sure that there are other CAS failure modes, but I would not expect the CAS to allow the car to run but prevent the car from cranking.

In particular, the fact that you get any sound from the starter indicates that the CAS is working. The start gets a crank signal from the car, then tries to turn over. There isn't a separate signal for the solenoid.

[Etansinsta]

had the same codes and it was starter fwiw

[Richneerd]

Same codes on my X3, changed the starter and ignition starter switch

Fired right up!

[dpaul]

Originally Posted by nrubenstein

Dead CAS means that the car is absolutely dead to the world. It's very similar to no battery. I'm sure that there are other CAS failure modes, but I would not expect the CAS to allow the car to run but prevent the car from cranking.

In particular, the fact that you get any sound from the starter indicates that the CAS is working. The start gets a crank signal from the car, then tries to turn over. There isn't a separate signal for the solenoid.

It is far from clear that the click the OP reports was from the starter/solenoid. Of course you are correct, a non-communicative CAS would leave the car dead to the world. But his is clearly not dead.

The simplest (not necessarily correct) explanation based on a careful reading of what the OP reports is that a MOSFET or some other type of silicon switching device has failed on the CAS motherboard so that Terminal 50 cannot be successfully activated. There are a number of threads on M3forum and e90forum describing this problem. Just to be clear the "signal from the car" that activates the solenoid comes directly from CAS and requires a fairly high current delivery.

Since the OP has ALREADY had the starter rebuilt, it seems unlikely to me that a replacement will remedy this situation. But of course, the person he took it to could have made an honest error of some sort or is just incompetent.