Crankshaft Sensor Testing/Replacement
 

I figured I would do a quick write up on my recent no start concern with my 93. The engine would turn over but would not fire and it turned out to be the crankshaft sensor.

There were no codes during the final failure of this part and I was having the following symptoms prior to complete no start failure.
1.) The car had a hard time starting when it was hot
2.) The car quit for no reason when driving, but would re-fire after extended cranking
3.) The car finally quit and would not start again

If you run into a similar situation where the engine turns over, but does not fire, there are few things to consider before looking at the crankshaft sensor. However in my situation, when I was doing the preliminary checks, I determined that all my other systems were working correctly, and I simply had no spark.

Crankshaft Description (As noted in 1993 GM Service Manual)
The magnetic crank sensor is used to determine engine crankshaft position. The sensor is mounted inside the block near a nine slot wheel on the crankshaft. The rotation of the wheel creates a flux change in the sensor which produces a voltage signal. The ignition control module processes this signal and creates the reference pulse needed by the ECM to trigger the correct coil at the correct time.

Step1: Removed the crank sensor connector/harness from ignition control module and probed terminals A and C on the connector of the wiring harness with an ohm meter. You are looking for a reading of 800-1200ohms. I had an open circuit indication.
(Note: To access this sensor, you need to remove the MAP sensor and bracket as well as the PCV hoses from behind the intake.)

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Step2: The FSM says less than 800ohms means the sensor leads have shorted together or the sensor is faulty. If you have a reading greater than 1200ohms, there there is an open sensor circuit or faulty connection at the sensor, or faulty sensor.

Step3: Since the crankshaft sensor is so inconvenient to get to, I decided that I would purchase a new one to replace it with since I would be under the car anyways. I went to Napa and picked up the sensor (Part# CSS109)


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Step4: As soon as I attempted to remove the sensor, the head broke off leaving the rest of the sensor inside the engine block. I attempted to extract the remaining piece of sensor with epoxy and a bolt, a screw, and o-rings piks. The sensor would not move, so I ended up having to drop the oil pan and punch the sensor out from the inside.

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Step5: After replacing the sensor and buttoning everything up, the car started and all systems checked out!

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Re: Crankshaft Sensor Testing/Replacement
 

Nice little write up. Did an ECM code lead you to this as a problem area?

Re: Crankshaft Sensor Testing/Replacement
 

Oh my goodness, I apologize for not answering that question GC. I must have missed the notification back when. Anyways, there was no ECM code that had every flashed up during that whole ordeal. I just had a no start issue and had to do the old fashion diagnosis with the help of the FSM.


No worries. I'm glad that I could add to the wealth of knowledge on here!

Re: Crankshaft Sensor Testing/Replacement
 

Awesome write up with pics. Thanks for closing this thread out. GC

Re: Crankshaft Sensor Testing/Replacement
 

Good diagnostic work...

Shouldn't there have been a DTC for CP Sensor? Even a History DTC, for out of spec parameter?

Re: Crankshaft Sensor Testing/Replacement
 

There wasn't any DTC's logged or in history. From my understanding there isn't a specific code for the CP sensor. The two codes that deal with electronic ignition appear to be DTC 42 (Ignition Control Timing Circuit) and DTC 36 (Electronic Ignition Circuit Missing).

The fault tree for DTC 42 has to do with timing above and below 400 rpm and the ECM, ICM, and ignition control (IC) signal. A 42 is set when IC mode isn't demanding a bypass of the system (like it should be), the ECM doesn't detect a IC pulse or no IC pulse detected by the ICM.

Similar to DTC 42, DTC 36 is engine timing in ignition control (IC) mode enabled at over 400rpm, or the ICM is not seeing the IC signal from the ECM or the ECM is not detecting the correct voltage on it's fault line to the ICM.

Neither DTC technical description or fault tree make reference to the high or low input from the crankshaft sensor either.

From my readings of the system design, I simply think it was a case of the sensor slowly packing it in... until it finally broke (open circuit) once and for all.

Here is my theory on this whole ordeal:

The occasional hot no start:

• The heat from the engine running and then shutting off was perhaps was causing some minor expansion or contraction with the sensor to cause a open circuit
• That OC obviously effected the ICM's ability to determine engine speed or crankshaft location. Without that, the ICM can't send a reference signal to the ECM and the ECM doesn't know which coil to fire.
• For some reason the sensors wiring corrected itself enough for the ICM to get a sync pulse and then she'd fire

Suddenly quit while running:

• Similar to above, the sensor would open up from heat or something
• Once it opened, the ECM doesn't know if the engine is running, so it cuts the injectors and therefore kills the car....then restart results in my first bullet list

No start:

• Sensor packed it in finally...
• Refer to first post :dancing

Truth be told, I'm actually grateful that she got me home. I was down in Montana on a road trip about 1000km or so away from home, in a different country no less. I had experienced those no starts while I was in Montana, but it eventually fired every time. I had finally got back into Canada and was1.5 blocks away from the house, the car quit again and I was able to coast right up to the alley way...then it was dead in the water for good.

BUT it got me home....just something to be said there.:icon_thum

Re: Crankshaft Sensor Testing/Replacement
 

No code if the engine isn't running.