Crankshaft Position Sensor trouble shoot

[WobblyElvis]

I have never had a problem with one of these before so I'm not even sure this is the problem.
1.8 litre VW Jetta 2002 . Was difficult to start a few days ago and today it quit at a stop light. Cranks but no spark at all. Removed a plug and it was dry. Unfortunately I ran the battery down and removed it for charging, so trouble codes are lost for now.

With a faulty crank speed sensor, the computer would call for no spark or fuel? It appears to have a 3 wire plug. Is there a simple test? Resistance test?

Would the camshaft position sensor cause identical results?

Probably working on it tomorrow.
Any thoughts are welcome.

 

[kschachn]

My BMW will do as you describe when the crankshaft position sensor is disconnected. No spark, no fuel no ignition. The BMW manual only gives a resistance check for the component.

My car will run with the camshaft position sensor disconnected, it just batch fires the spark plugs to compensate. But it will trigger a CEL even in my old OBD-I system.

 

[WobblyElvis]

Originally Posted By: kschachn
My BMW will do as you describe when the crankshaft position sensor is disconnected. No spark, no fuel no ignition. The BMW manual only gives a resistance check for the component.

My car will run with the camshaft position sensor disconnected, it just batch fires the spark plugs to compensate. But it will trigger a CEL even in my old OBD-I system.


This is helpful information.

 

[RooflessVW]

The simplest test for the CPS is to replace it.

Here's a good link if you want to go through the trouble.

 

[Superflop]

For a completely gone cps there are rarely codes unless you had say a random misfire code.

Failed cps typically stops injectors from firing due to loss of synchronicity.

Since the cps if an off and on switch the ecm cant tell if its bad or not. Typically you can ohm them out to determine failure.

On my saab i just keep a spare in the trunk along with the torx bit and wrench i need to change it.

 

[WobblyElvis]

This vehicle was suffering from some random misfires. Sounds like I'm on the right track. I'll do a resistance check and I can check if it generates a signal when the engine is cranked. Good info from rooflessVW thank you.

 

[Superflop]

Oh and if you have a failed cps the tach will typicaly be inop during cranking

 

[clinebarger]

Originally Posted By: Superflop
Oh and if you have a failed cps the tach will typicaly be inop during cranking


With a early 2000's model vehicle.....I agree, Though a lot of the later ECM's could replicate CKP signals based off the CMP sensor/s output.

Case in point.....I had a 2008 Dodge Ram 3.7L come in with a CKP sensor code (Hard fault), Extended high idle, & a Long Crank.
The CKP senor was DEAD, Steady 5vdc on the signal circuit while running. Scanning the data was useless as the "Crank Hi/Lo & RPM signals" were being replicated.

This being a 3-wire CKP....I would guess it's Hall Effect?, 1 wire would be ground, 1 wire would be supply voltage (12 or 5vdc), The 3rd would be the signal circuit.

*Quite a few manufactures use a "Bias Voltage" on the signal circuit via a Resistor connected to the same power supply the sensor is running off of.

 

[WobblyElvis]

The Plot Thickens...
This is my son's car, he bought a CPS before I could test the old one so we put it in. It cranked with no ignition but this time we could smell fuel. Checked everything but still no go. Finally I disconnected the battery and touched the pos and neg leads together to drain any residual charge from the computer. Fired right up ran for a minute or two and quit. Wouldn't start so did the POS NEG trick again and it started. Ran for a while and stuttered but kept going. Quit and restarted with ease. Let it run for about 20 minutes more without a problem.

No trouble codes set. Don't make no sense to me. I'm guessing the computer is done.

 

[Wolf359]

For that type of part, was it OEM or aftermarket? I know on Mercedes they used to have problems with those in the first few years and then they redesigned them. Aftermarket ones would cause problems, but the newer OEM ones would be fine. For crankshaft and camshaft sensors, I'd always use OEM.

 

[WobblyElvis]

I believe the part was made by Standard Motor Products, but like anything these days, probably made in China. This car has a value that fluctuates with the price of scrap metal, so unless a miracle happens, it won't be around for long.