Hello.

I am getting no crank/start in my R56 MCS 2009 Non-LCI, N14. The car has been parked since around September of last year, just got it going again about a week ago after having diagnosed a no crank/start problem, and finding out it was a bad ground signal. I moved around the engine block ground strap and this fixed the issue the first time (went from a 3V signal to block -> 12V). It was test driven maybe 5 times, and now I am back to the same problem again, but the ground signal to block is fine, also tried moving it around again just in case.

Interior lights do come on, and when hitting the start button a large audible click is heard... Not every single time, but give it a few minutes and try it again, and the click is heard again.

A lot of work has been done to this car since it was driven regularly last year, but the car has started and been driven a bit SINCE this work was done… some of the potentially relevant work done: New Alternator, Oil Filter Housing, Battery (still have the old one, tried both)

I will outline below what I have tried.

Fault code:
CAS/EWS: A0B4 - Engine Starter Operation
(No other relevant codes are present at this time, though we were getting a “No BSM Message from Generator” code before, do not remember the code, this is gone now)

- Bench tested starter, works fine.

- 12V being received from CAS module through white signal plug when pressing start.

- Engine block/starter should be properly grounded now, getting 12V reading from POS battery terminal to engine block/starter

- Removed and visually inspected CAS module, all pins are present and wires look healthy, I know this one was a long shot, since I am not sure how to test this on the bench. Also tested the Omron relay on the CAS, clicks when presented with 5v across the coil pins.

-Engine Comp fuses intact

What do you guys suggest I do next? I suspect the CAS module is fried, because of all the attempts to start while not being properly grounded, finally took its toll on the CAS. Really hoping this isn’t the case as it’s very expensive to replace the CAS!

I can post pictures or videos this weekend if needed.

Thank you!

 

What year MCS?

 

Edited main post, 2009 MCS. N14

 

What voltage do you read between the two battery posts? If the voltage is 12.5V or higher try the test below.

Do you have some good jumper cables? If so, secure one clamp to a clean part of the block (e.g., lifting eye) and the other to the (-) battery terminal to bypass the ground strap. Does the engine now crank and start?

Your starter solenoid clicks and receives 12V, so the CAS is not a prime suspect.

 

I will try this as soon as I get home and report back, great idea! Might be a dumb question, but even though the voltage reads the same voltage between the battery posts, and positive terminal to block, just using the ground strap, it could still be a bad grounding issue?

I am not entirely certain I tested the starter solenoid properly, I just unplugged the white wire, and probed the end of it, while pressing the start button, this is where I was getting a 12V read, to me, this confirms the CAS is not at fault because it is still sending the 12V signal, which is its primary purpose in this case. ALSO, I am not sure if it necessarily "clicks" each time I press start, but it definitely does make a loud click if you try it once, then wait a few minutes and try it again.

Also something else I failed to mention, is, when pressing start and measuring voltage from B terminal on starter to ground (ground on both battery terminal and starter assembly), voltage drops from 12V to 1V/0V momentarily then back to 12V... This seems odd, shouldn't it only drop by around 0.5V?

 

Not a dumb question at all. Static voltage tests are not very informative when testing a high amperage circuit like the starter circuit. The more informative test is the voltage drop test. But for now, the jumper cable test is easier. If the engine cranks with the jumper cables connected, you can use a voltage drop test to locate the excess resistance in the ground circuit.

Your starter solenoid white wire test is convincing.

Have you already verified that (1) the nut that secures the red starter cable to the starter is clean and tight and (2) that you are able to turn the engine by hand?

This^ observation is potentially very important as it may indicate a problem with the red power cable that delivers battery voltage to the starter motor. Start by checking the connection of the red cable to the battery and to the alternator. Is either loose?

 

I just re-installed the starter, and in the process re-tightened the starter bolt to the stud on the starter. It is quite rusty and could be losing contact, I will take some sand paper to it and make sure it has a clean connection.

The engine was just rebuilt not too long ago, and had been running fine, I don't think there's any reason to assume it wouldn't turn by hand, but if the other tests don't prove successful I will do that next.

Thank you so much I will reply back here in an hour or so with my results

 

Good luck!

PB Blaster and a wire brush may be more effective than sand paper.

 

Voltage at battery posts read 12.06v. Brand new battery.

jumping Ground to engine block did not make the engine start.

 

Charge the battery to 12.6V before trying to crank the engine.

 

I will leave it on the charger longer, but I just charged it for a few minutes to get it up to 12.7 and tried it, no start.

tried it with crank assist on the charger, and it sparked at the battery while doing lots of those loud clicks I was mentioning.

 

Is it possible to perform a voltage drop test with only a multimeter?

 

At this point, have you cleaned all rust from the (+) starter stud and the red cable terminal that attaches to stud? Those two items must be very clean bare metal. If so, did you then bypass the ground strap with the jumper cables, charge the battery to at least 12.6V, and then attempt to crank the engine?

Yes, you can use a good digital multimeter to do a voltage drop test. You will need a helper to press the start button while you make voltage measurements under the car.

Try this test: Disconnect the red cable from the starter motor but leave the white wire solenoid connector plugged in. Do NOT let the disconnected red cable terminal short to ground. With the battery charged to at least 12.6V, then press the start button. Do you still hear the loud click?

 

I just jumped positive terminal from the battery straight to the starter, and it cranked and wanted to start right up. Doesn’t this pretty much immediately tell us that a connection to the starter through the cable isn’t making a good enough connection? I cleaned the end really good, it’s making a nice solid connection at the starter.

 

That's great progress! There's excess resistance somewhere between the battery (+) post and the starter motor (+) stud. Is the red cable in bad condition?

 

So… I literally JUST had it crank when jumping from positive on battery to the starter… checked all the connections, all is good (cable looks like it’s in good condition), still no crank when everything’s hooked up normally… so I’m like okay wtf… tried to jump positive again, now it won’t crank.

i have the new starter here now, im going to put this in now and see what happens, maybe the stud on the starter connection is just messed up inside or something… (it does wiggle if there’s no nut on it)

 

Current condition of the starter upon removal. The strap leading to the motor is very corroded by the looks of it.

 

Yeah, those pictures suggest the starter may be the issue.

 

New starter installed. Same issue.

 

Did you bench test the replacement starter before installing?

If so, try the jumper cable bypass tests again, but carefully avoid accidental shorting to ground of the (+) cable.

 

 

I did not bench test the new starter. Definitely should have though.

 

I just did the ground jump again and SHE CRANKS! And she cranked again I had to make sure haha!

so I need to re-do the grounding strap probably?

 

You're close. Buy a new ground strap and possibly new battery cables. They all seem to show some evidence of corrosion. Clean the block and chassis connection points before installation.

 

I was looking a little bit ago for battery cables, they look expensive for OEM. Do you have any suggestions? Also it looks like they run up over to the front of the engine to attach to the alternator all in one connected mess. Going to probably be a day project!