Hi, long time forum stalker first time poster. I picked up a 98' C5 convertible awhile back that needed a lot of help. I've been working through it all with a lot of help from previous posts on this forum but haven't found anything to help me with my final issue. The car always seemed to start right up or sometimes take a sec longer cranking to start. Checking the codes it popped up a cam positioning sensor code which made sense with the occasional longer cranking time to start depending on whether it was on the exhaust or intake stroke. I've taken the intake off to change the cam positioning sensor but figured I'd better check the plug and I noticed with the key forward I'm not getting 12 volts at the plug. I'm assuming that the wires have broken somewhere in the loom and instead of opening up the whole loom I'd just run new wires and install a new pigtail. Can anyone give me the wiring colors and locations of these wires? I'm assuming one comes directly from the pcm and one goes to ground and the other to the crank position sensor? Any and all help would be appreciated.
One last thing, since I have the intake off to get to the cam positioning sensor and wiring I removed the fuel pump relay to not spray fuel everywhere. This isn't something that would effect the sensor would it?
Thank you in advance......

 

Mike,
Yes, a bad cam sensor can cause longer crank times. The CMP is a 3 wire Hall Effect Sensor. On your '98 at the pigtail connector the brown/white wire is your signal wire, the red wire is your 12 volt feed and the pink/black is sensor ground. ALL go to the PCM !!!...So you're saying with key ON you don't see 12 volts at the RED wire ??...that is your B+ feed from the PCM...are you seeing NO voltage or LOW voltage ??...if NO voltage you have to go to the PCM and see if you have 12 volts there...if you do there is an open somewhere between the PCM and PIGTAIL connector. That's my bet. The CAM and CRANK sensors share the same 12 volt feed from the PCM so if there were no 12 volt feed the crank sensor would not work and you would then have a "cranking-no start" !!....BTW, all 3 wires from each sensor and not shared externally but do share a 12 volt feed and sensor ground internally inside the PCM.

TO TEST: KEY "ON" - 12 volts at Red B+, LESS than 100 mv on signal ground...if more than 100mv there are 4 PCM grounds on the '98 that would have to be checked !!... the signal wire should be a "pull up" circuit design like the crank sensor signal. Hook up multimeter to signal wire and a good ground...you might see .02-.03 volts...now with multimeter leads still connected take a 12 volt test light connected to battery POSITIVE and touch the tip of the test light to the lead at the brown/white wire...the multimeter should now show 12 volts...if it does the signal wire is good !!

The PCM locations for a 1998 are:
1) brown/wire signal- pin 4 (C1 connector)
2) red B+ - pin 4 (C2 connector)
3) pink/black- pin 70 (C2 connector)

 

This is exactly the info I was looking for, thank you very much! The car ran so definitely getting feed to the crank sensor, I will follow your steps when I get home this evening and get back to you. Again thank you much, I love this forum....

 

Mike,
SUPER !!!...if you have a question I'll PM you my number...feel free to call tonight !!

 

I pinned the red (pin 4-c2) wire at the PCM and had 12 volts there. Must be a break in the wire somewhere so I ran a new one to the cam positioning sensor. Now have 12v @ the pigtail.
I continued to follow your directions by connecting my multi-meter to a GOOD ground and the brown/white signal wire, .025 volts.
I clip my test light to Battery+ and touch the tip of my test light to brown/white signal wire and DON'T have 12 volts. It's reading .73v.
I test the signal ground pink/black at the pigtail and DONT read 100mv either, I'm reading same as signal, .025 volts.
I'm going to run new wires for the signal & signal ground and use the new cam positioning sensor pigtail that came in today as well.
I would like to get the PCM grounding locations you mentioned earlier if you don't mind?
Thank you very much for the help Rob!
It is much appreciated.

 

Mike, .025 volts is 25 Mv so signal ground is good...less than 100 !!...so I guess you must have an open in the B+ since you had 12 at the PCM but not at the pigtail..as far as the signal wire I found this video !!...get a piece of metal and follow testing in the video !!...with new CMP sensor if test is no good we will have to check the signal wire from the PCM to the pigtail !!

 

I went and mowed the lawn and decided to check back to the forum before I started running new wires. Glad I did!!! Lol!
I followed the video and we're all good,!
I wish I could buy you a beer Rob for all your help, living on opposite coasts though that won't happen today. A simple thank you is all I got, thank you sir, thank you much!

 

Mike, SUPER !!...when everything is running let us know if CMP is working and if the car starts right up !!...and this sums up my motto...”TEST...DON’T GUESS”...LOL !!