Expert: Roland Finston - 12/24/2011

Question
Hi Roland. I have a 98 Cirrus that has developed a worsening condition where it will cut off while driving and won't restart. There is no spark and there are no codes on my OBD-II scan tool. I have switched the relays for the fuel pump and ASD with others. Since the tranny had just been rebuilt I suspected the CPS circuit and backprobed the Grey/Blackstripe signal wire at the PCM. It reads .31V with the key off???. While probing and turning the key it stayed at .31 briefly and then jumped to 4V and the car started but then it dropped back down to .31V again. Should it not start at 0V with the key off and read 4V while running?

Answer
Hi Mike,
That wire carries the crankshaft position sensor signal. My understanding would be that when the key is in the run position you should see it oscillate between 5v and O.3v as you turn the crankshaft by hand with a socket on the crank pulley bolt. I don't know whether it should read anything other than 0 with the key in the off position which is probably not relevant in any case.
So I would not interpret the reading with the crank sitting statically but rather while you turn it slowly by hand. Of course you would need an oscilloscope or similarly pulsed voltage detection ability type of unit to measure the signal at idling rpm.
Have you checked the egr valve to see if the stem might be stuck ajar? That can cause a stall when you slow down and also a refusal to restart, without setting a code? Try spraying some WD-40 on the stem where it enter the body of the valve and move it back and forth with the tip or a screwdriver inserted in the slot that circumscribes the stem.
Roland