dont understand why you need to do a crank relearn when you change the censor.isnt the job of the censor to know where tdc is at on #1 at all times?if this was in question it wouldnt run at all.if someone could clear this up for me it would be a big help.I had recently changed mine,havnt done a relearn yet,wondering what it would change.

just so there is no confusion its the same truck in my sig. 2001 8.1/alli

Not all sensors are the same... the crank and cam sensors need to be in synch, changing one throws that synch out the window. Most relearns consist of idling engine then flooring pedal till ECM cut off. Usually need a scanner hooked up for it to be done correctly.

It will run ok without the relearn but usually improves enough to notice a smoother running more powerful engine once it's done. I do them all the time as part of a regular tune up and just relearning a worn in sensor makes an immediate improvement in idle and power, and this is after the hard parts are in.

Vernon

Them answer's is correct, the 8.1's were noted for crank sensors too.

My Check eng light isnt on after swapping pcm's. The paperwork from w4me said it would be. Im going to do a crank relearn anyway if it helps improve how it runs.I can't see my truck idling any smoother than it does now,its like a lexus idling,you cant feel it running.

i changed mine 6 mo ago and no relearn.runs great.

gm sent me a letter that they recalled the crank sensor

thanks for the info,I will do a relearn,(I have efi live) so its easy.thanks again

You don't need a scan tool to do a relearn. Just follow these steps:

1. Turn off all of the accessories. With the Air temperature sensor and Coolant temperature within 5 degrees (Centigrade) of each other, start the engine and let it idle in Park or Neutral for two minutes.
2. Accelerate the vehicle to 55 mph at part throttle. Cruise at 55 mph for 8- 10 minutes until the engine reaches operating temperature.
3. Cruise at 55 mph for another 5-6 minutes.
4. Decelerate to 45 mph without using the brakes, and maintain 45 mph for 1 minute.
5. Perform 4 deceleration cycles, without using the brakes, of 25 seconds each where no specific speed is necessary. Returning to 45 mph for 15 seconds in between deceleration cycles.
6. Accelerate to 55 mph and cruise for 2 minutes.
7. Stop the vehicle and idle for 2 minutes with the brake applied and the transmission in Drive (automatic trans.) or Neutral (manual trans.) with the clutch depressed. Refer to diagram A on page 8.

You don't need a scan tool to do a relearn. Just follow these steps:

1. Turn off all of the accessories. With the Air temperature sensor and Coolant temperature within 5 degrees (Centigrade) of each other, start the engine and let it idle in Park or Neutral for two minutes.
2. Accelerate the vehicle to 55 mph at part throttle. Cruise at 55 mph for 8- 10 minutes until the engine reaches operating temperature.
3. Cruise at 55 mph for another 5-6 minutes.
4. Decelerate to 45 mph without using the brakes, and maintain 45 mph for 1 minute.
5. Perform 4 deceleration cycles, without using the brakes, of 25 seconds each where no specific speed is necessary. Returning to 45 mph for 15 seconds in between deceleration cycles.
6. Accelerate to 55 mph and cruise for 2 minutes.
7. Stop the vehicle and idle for 2 minutes with the brake applied and the transmission in Drive (automatic trans.) or Neutral (manual trans.) with the clutch depressed. Refer to diagram A on page 8.
sounds like you can do a relearn by accident,,,,thanks for the info thats very helpful

While that may be true, based on experience trying to perform drive cycles in the real world rarely works. If you have a chassis dyno then it may be easier. I don't know if you have to follow those step exactly or what but if any traffic pattern interrupts that sequince it will not work. I've wasted a lot of time on many different makes trying to get a drive cylce completed. Every once in a while if it's really simple and my geographical area is conductive to it I can get one off. As an example I've had a friend with a 2006 truck that had idled rough since day one with over 30K come over and only get a relearn then drive off with a smooth idle.

Vernon