2007 GMC Sierra Classic 2500HD 6.0L U code engine SLE 4WD CRANK BUT NO START

Mice living in the UHBEC, MAP airbox, inside the dash & A/C Evaporator housing (nest plugged the drain and the tray filled with water) and somewhere under the seats. They chewed insulation on a couple of the wires underneath the UHBEC and I couldn't find any other chewed wiring. I repaired the damaged wires and the only DTC it's throwing is P0336 (Crankshaft Position Sensor reference circuit performance). The truck ran after draining the evaporator tray. Started the truck moved it 150 feet. Parked it and hasn't started since. Talked with a friend who is a mobile service tech and he thought since it didn't show any RPM indicator when cranking that the CPK was defective. Towed it into my garage and replaced the CPK .... STILL NO START same P0336 DTC. Over the last four weeks I have trapped 4 mice inside the cab and have traced the CPK wiring (all OK). Bought new Autel MAXIdas 808 Scan tool to assist with running the flow chart from Mitchell DIY and the diagnostic chart for the Crank Position Sensor. The only discrepancy I've found is that the 12 volt reference circuit to the CPK shows a voltage drop of 1.5 volts at the PCM output. STILL NO START. Mitchell DTC chart says that PCM needs to go.
What am I missing??

im looking at a wiring diagram do you have a purple/white white/black and gray and black wires at the crankshaft sensor?? you should have a 5 vols on the purple/white wire. a ground on the white/black wire. and a signal on the last wire its either a pull up or pull down design.

Hi Cheryl, My harness is coded differently. My Ltgrn=12v ignition. dkblu/wht= CKP signal, yel/blk=5v ref. Ltgrn shows 10.9v at the PCM output and the CKP sensor input. Still no crnk.

Now I have a U1000 class 2communication failure dtc. Still have no start and the P0336 CKP sensor code.

According to Mitchell, the yel/blk wire should be LOW REF (ground).



Cheryl, I believe, you are looking at the 6.2L

Do you get any voltage fluctuation on the CKP signal while cranking?

woops. i was my mistake

Hi Pole71
The ground on the yel/blk is good at Pin 21on the PCM. The ltgrn shows 12.03 at the Pin 2 on the PCM and 12.9 at the battery. The dkblu/wht does have varying voltage between 2.3 and 4.6 volts while cranking. Still stumped.

Ok. Let's cover the basics. When you are cranking, do you have sufficient fuel pressure? Spark? Injector pulse?

P0336 sets when the PCM detects that the CKP sensor signal is inconsistent for 3 seconds. If you clear the code, does it come back, immediately?

Check to make sure the CKP wires are not routed to closely to secondary ignition wires, ignition coil, or anything else that can cause some electromagnetic interference.

Hi pole71
Yes I have fuel pressure. The fuel pump runs while cranking. NO SPARK. Not sure about injector pulse. Haven’t chased that yet but I believe there is injector pulse as there is a real heavy odor of raw fuel after cranking.
The P0336 code returns immediately upon the next 15 second crank after clearing it with the scan tool.
I’ve checked the routing on the harness and can’t see anything that might have shifted or that might cause electromagnetic interference. The truck ran. Was parked for two days and will not start. It’ll crank all day long if you keep the battery charged. I can’t reach the camshaft sensor to backpin it and see if it might be the cause of the problem. It doesn’t share the same reference circuit as the crank sensor but they say it can cause the same DTC to get set. The CRANKSHAFT POSITION SENSOR was replaced five days ago.
I’m sure that this is really something stupid easy to fix but I just can’t seem to find it. I really, really hate mice.

Just a heads up I don’t have a lift and I’m chasing this on my back with the truck up on jack stands.
I hate to think that with about twenty five hours into this I don’t have any more results than when I started.
Pretty sure that all the powers grounds and fuses are all good.

Since you can't access the CMP sensor, here are the pin locations and colors for the CMP signal and low ref.

The RED wire on pin 39 of connector 2 is the IGN FEED.

Have you checked power and ground at the coils?

Hi Pole71,

Thanks for all your help and encouragement. My insurance company has stepped up to resolve this situation. I did check the cam sensor and it checked out OK. I put the underhood fuse box back together and everything went piffft. NO CRANK AND NO START and the PMC passed the system test. Now the engine live data can't find a crank request when the key is turned to start and the whole instrument panel lights up like a Christmas Tree and NOTHING. The tow truck came and took the truck to the dealer shop. They'll have the pleasure of finding the short or open that is deep in the wiring harness. Winter is coming and I need this truck to plow.

I promise to keep everybody up-dated on the situation and the results of the restoration of power.