2010 BMW 528i - No Start Problem

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liljoe
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2010 BMW 528i - No Start Problem

Post by liljoe »

I have a 2010 BMW 528i in here that came on the hook for a no crank, found starter to be defective so we sold and replaced it.

Got it on and car will now crank but not start most of the time. Sometimes it will start and run but mostly not. Scanned it and found a code for crank sensor. Checked for cranking RPM on scanner and had none when it would not start. Hooked to CKP signal wire at PCM and have a real nice looking square wave with one long notch in it like it should be but no RPM on data. During the course of testing I removed crank sensor and hooked to signal wire, with sensor removed and not near a metal trigger I had 5 volts. Using a wrench to trigger the sensor it would toggle from 5v to 0v like it should but sometimes when I would remove the trigger metal, the voltage would be 5v and others it would be 0v. Now if the sensor is doing this the PCM would not be able to determine if the sensor was on a slot or a trigger spot on the crankshaft cause it might be 5v on notches or it might be 0v on notches. I got a new sensor from BMW and it does the same thing. I checked the power supply to the sensor and also the sensor ground that goes to PCM. The supply voltage is steady within .2v of battery and the signal ground is showing a steady 0v on the lab scope even during cranking. According to customer the car ran fine before the starter went out.

Anyone got any advise on this one? It is making me doubt my abilities big time....
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ricmorin
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Re: 2010 BMW 528i, no start problem

Post by ricmorin »

You had the intake off for this one, right? Check crank signal right at PCM. Maybe something got dislodged during the intake removal?
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liljoe
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Re: 2010 BMW 528i, no start problem

Post by liljoe »

ricmorin wrote:You had the intake off for this one, right? Check crank signal right at PCM. Maybe something got dislodged during the intake removal?
That is where I am doing my testing.....
The signal not being the same each time is what I am having trouble reconciling in my mind..... One time the sensor is at 5v when not near metal and others it is 0v under the same condition....
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Re: 2010 BMW 528i - No Start Problem

Post by ricmorin »

I wouldn't sweat that. Although I've never seen it, I've heard of signal inversion being common and not an issue. The PCM is looking for voltage swap, not polarity.
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