2000 s-10 blazer. Just finished rebuilding and installing trans, changed rear main seal, timing chain and differential seals. I took the differential out to do the job. All is together and now, no spark. I went through the ignition test procedures. I found a grounded driver circuit and fixed. Procedures told me to replace ignition module and I did ($72). Problem not fixed. Pink to ground on crank sensor has power. Pink to both other wires on crank sensor also show as other wires being ground. When I check other wires to ground for resistance it shows open circuit. I don't know what these leads are? It ran good before the other repairs? The grounded driver circuit at the coil harness was caused by a lead spliced in for a remote start. I cut the lead off and fixed the wire, now all tests good, except no signal? I haven't removed the remote start yet. Is there some other reason the vcm wouldn't be sending a signal. At the vcm white (procedure said clear) harness the top middle I believe is the timing signal and it tested ok. I believe it has something to do with my work, since it ran before. I was really expecting to see no ground. I don't want to replace the vcm. Any suggestions.

I didn't do anything to the distributor since no spark at coil.

 

I suggest you look at the OBDII trouble code diagnosis links and look at PO336, that'll give you an explanation of the wires and their functions for the crank position sensor. I don't know any backyard mechanic testing techniques. If you had a code reader with the ability to read active and pending codes it might give you a direction to move in?
I don't know what diagnosis chart you have so I may be preaching to the choir but some things you can try in no particular order:
Disconnect the ICM, set a DMM to the A/C scale, grounding one side, connect to the white wire of the harness. With the engine cranking you should see 1-4 volts, that's your timing signal. Check the pink in that harness for 12v (same fuse for the CKP so we know it should have power) With the ICM connected, with a test light, check the wht/blk and pink at the coil and see if you have a pulsing light when you crank it. Disconnect the cam sensor on the distributor and check from the pink to ground for power (ENG1 fuse powers that).

 

I tested the coil driver wht/blk to positive on battery while cranking engine, not to the pink wire. No signal. Would the distributer and cam sensor affect the coil driver circuit? Does the coil driver circuit run through the cam sensor? How do you test the crank sensor while cranking engine? Crank sensor was replaced less than 3,000 miles ago. Thanks!

Those trouble code links are very helpful, Thanks. I'll have to take a look at the cam sensor and distributor. I could have damaged it while putting in the trans fill tube in or tilting the motor. It looks like the vcm might not send a coil driver signal if it doesn't see cam rotation?

 

Unfortunately the only way to test the crank sensor is to connect an inline harness & check the duty% according to the FSM. GM harness and GM tester, I don't know what they mean by duty percentage and I don't know whether the test harness goes inline with the sensor wire? That why I was hoping for a code, your PCM knows if a sensor is disconnected (usually). Before replacing it the thing to do would to be disconnect the wires at the PCM and check for continuity to the cam and crank sensor. I don't have that info where I am at the moment (connectors and pin#'s) Check the coil driver wht/blk at the coil relative to BAT, the coil has a full time 12v thru the pink, the ICM is a switched ground to charge the coil for a spark. And yes, you need both coil and crank sensor input.

 

On the crank sensor harness both pink to yel and pink to ppl were showing voltage, yel and ppl acting as ground with ignition on. Yel and ppl to frame showed no continuity, so no short, correct? A wiring diagram is on the OBD diagnosis link. Can a remote starter interrupt the coil signal and still allow the starter to turnover?

 

A remote starter will provide a constant 12v to various things (ignition, radio, blower, etc.) but 12v to the starter relay until it's started. That wire tapped into the ICM is a "run sense" or "tach sense" depending on the term they use. My remote start seems to power everything with the exception of the wipers, I didn't install it so I dunno how they did that. I'll guess a remote start could kill the coil by grounding the driver if it became shorted internally but normally it shuts things off by simply removing the 12v inputs (from the remote start) at the ignition switch. As I read the descriptions of system components the crank sensor provides a signal 3x per revolution to the PCM. The cam sensor 1x per cam revolution (or 1 for ever 2 crank revolution) I mention this just to add "CMP sensor will not affect drive-ability, it's sole purpose is to provide the VCM with necessary information for misfire DTCs" Here I was hoping for something simple like a pinched harness...... Not to ask a silly question but re-reading your original post I see you replaced the timing chain. Maybe you ought to remove the crank sensor, turn the motor and see if you can see the reluctor wheel passing by the hole?

 

Well, I changed the crank sensor today and still no signal to coil. All wires check out good. All voltages check out good. I can see the reluctor through the timing cover, the tabs pass directly by the middle of the hole. The clear connection at the VCM has some discoloration, no distortion, in the clear plastic around the 2 ground pins on the harness, but they test good to ground. I didn't check the light fuses but I believe I checked all relevant fuses. Could the VCM gone bad when reconnecting the battery after I finished all my work? I made the mistake of having the ignition on when trying to connect the battery and it sparked quite a bit. Had the steering unlocked during before mentioned repairs and forgot to shut the ignition off. I don't have a scanner. I don't want to pay to tow it to someone who does. It looks like the VCM to me, but its very hard to believe. Any suggestions before I possibly replace a good VCM. Thanks!

 

I purchased a scanner! P0336 sets as pending DTC while cranking and clears when I shut IGN off. All wires check out good no shorts to positive or neg, with good continuity. AC voltage measurement is a little low on white wire from VCM to ICM. My old analog multi-meter reads .5 volts on the 10 volt AC setting. I think crank position sensor clearance with new timing cover has changed to much for VCM to send proper signal. Could a CASE relearn fix this?

Help anyone?

Thanks!

 

Blazer is up and running. I figured out a way to test the crank sensor (2000 Blazer). I unplugged the blue harness from the VCM and ran a wire from pin 28 to the battery ground. I then ran a wire from pin 31 on the same harness and another wire from the battery ground to the cab where i could hook up my multi-meter (ING has to be cranking or in run pos. to power the sensor) and turn over the engine and see what was happening (no helper). With the CKP hooked up, I could move the sensor toward and away from a bolt and watch the multi-meter. The signal wire changes from ground to voltage when the sensor is close enough to metal which effects the magnetic field. Now that I knew everything was working I could observe the multi-meter with the sensor in and crank the engine. The timing cover I bought from Autozone (made in China) was out of spec. With the sensor all the way in it was still to far away. I modified the flange on the sensor a few times with a file (took off about 1 mm) before I got it right. I figured a lot easier to modify the sensor than to remove and replace the timing cover. I hope this helps someone!

BE AWARE OF AUTOZONE MADE IN CHINA TIMING COVERS.