LS motor crank sensor

I just put my truck back together after replacing the clutch, timing chain and have the trans rebuilt and it broke the crankshaft position sensor. I started this project due to the springs in the clutch hub coming apart and jamming bertween the clutch and flywheel. The main shaft of the trans was bad as where the bearing for the mainshaft. The truck has 180,000 miles and has been trouble free up until this point. The truck is a 06 GMC Sierra with the 4.8 and a 5 speed. On my test drive the truck ran good except for an exhaust manifold donut leak but then about a half mile from the house it made a strange mechanical sound and died. I towed it home and ran the code which indicatred a bad crankshaft position sensor. The wiring looked fine so I bought a new sensor. When I removed the old sendor I found that the end nearest the crankshaft was broken and missing with signs that it contacted the crankshaft (not good). I checked the hole and everything was clear so I installed the new sensor to see if it would run. The truck started but will barely idle and is missing badly. Has anyone run into this broblem before? Has anyone heard of an LS engine crankshaft contacting the crank sensor?

If memory servers me right (probably not), but the the later LS motors had the reluctor wheel at the back of the crankshaft. And if run out on it is off by just a smidge, it would cause anything from bad idle to a no run condition . . . Sounds like the crank sensor may have had contact with the reluctor wheel.

The only fix was R&R the wheel at the back of the crank

But I may be wrong on that . . .

Remember there are two different trigger wheels, a 24X and a 58X, and each takes a different sensor. IIRC, the trigger wheel diameter between the two is a smidge different. So the wrong sensor with the wrong wheel equals broken sensor.

BTW, all LS motors have the trigger wheel in the same spot.

Edit: after rereading, I think you have jammed the trans back in and caused a runout condition and killed the sensor. But also the trigger wheel is just pressed unto the crank, so it could have very well spun and is now off a bit which causes the rough running condition.

B: Thanks for clearing that up . . .

The Gen III engines featured 24X reluctor wheels and the Gen IV had the 58X reluctors.

• 97-05 = Gen III = 24x
• 06-Present = Gen IV = 58x
• 05 LS2 = 24x

In reply to Ranger50:

This is kind of what I am afraid of. The trans slipped in easily but it was a real struggle when I took it off. It was sticking on the alignment pins. Is it possible for the runnout to be bad enough to cause the crank interference. I would think that the rear main bearing would have to be pretty bad for that to happen. It is possible the rear main is worn with the miles on the motor and the fact that the trans had bad main shaft bearings but the oil pressure is still good.

In reply to Strike_Zero:

I looked at some pictures of reluctor wheels online and even though my truck is an 06 it has a 24x reluctor wheel judging by what I saw thru the sensor hole.

There is a Crank Position learn procedure you need to go through. One with a GM Tech2 or similar software, and a manual method. If memory serves me correct the manual method is to disconnect the negative battery cable, let the everything reset. Turn car on, rev to 4000rpm until engine speed decreases on its own. Shut car down for at least 15 seconds then start it back up.

IMPORTANT: While the learn procedure is in progress, release the throttle immediately when the engine starts to decelerate. The engine control is returned to the operator and the engine will respond to throttle position after the learn procedure is complete.

Install the scan tool. Apply the vehicle's parking brake. Block the drive wheels. Close the vehicle's hood. Place the vehicle's transmission in Park (A/T) or Neutral (M/T). Idle the engine until the engine coolant temperature reaches 65°C (150°F) . Turn OFF all the accessories. Apply the brakes for the duration of the procedure. IMPORTANT: If the CKP System Variation Learn Procedure cannot be completed successfully, refer to DTC P1336 Crankshaft Position (CKP) System Variation Not Learned for additional diagnostic information.

Enable the Crankshaft Position System Variation Learn Procedure with the scan tool. Slowly raise the engine speed to 4000 RPM . Immediately release the throttle when the engine speed decreases. Turn OFF the ignition for 15 seconds after the learn procedure is completed successfully.

Alot of the F body guys and most of us LS swapped guys just turn that code off on the ECU with no ill effects.

I've yet to hear of someone who actually needed to do the learning procedure because the car was running poorly and that fixed it.

I'm saying for the guys who still need it...

Thanks for the info guys. If the reluctor needs replaced (which would require removing the crankshaft) I think I will just put in a replacement engine as this one has a lot of miles on it and 4.8's are pretty cheap. I will probably drop the oil pan next week to check for damage and runnout on the reluctor before giving up on the engine.