Originally Posted by 06MonteSS (Post 277913)

yes, you should absolutely do it! Not running the relearn procedure can cause idle and performance issues...

A CASE relearn is needed when you replace your original PCM (or the actual crank sensor). The vehicle is driveable without the relearn though you will usually get an SES light. The CASE relearn can only be done with the PCM installed in the vehicle in which it will be used. It's a way for the computer to learn a parameter (Crankshaft Angle Sensor Error) that is unique to each particular engine.

The core program from PCMforless/Intense is probably the most common reason you'd need a CASE relearn since you're permanently replacing your original PCM with a tuned PCM.

If you have access to a GM TechII scan tool here is the case relearn procedure:

Connect a scan tool to make sure there are no trouble codes stored in the computer’s memory. If there is any power train trouble code other than P1336 (Crankshaft Position Variation not learned), the computer will disable the relearn function until the problem that aused the code has been eliminated. Also, make sure that the engine coolant (check it when the engine is cold) and oil levels are at an acceptable level.

1. Set the parking brake and block the drive wheels. Make sure that the hood is closed.
2. Start the engine and make sure that the engine coolant temperature is at least 158 degrees F. (70 degrees C.)
3. Turn the engine off for at least 10 seconds.
4. Select the crankshaft position variation learn procedure (CASE Learn)on your scan tool.
5. Make sure that the transmission is in Park. Start the engine.
6. Apply the brakes and hold the pedal firmly.
7. Follow the scan tool instructions.

Remember: That you are going to increase the engine speed to approximately 3000 RPM, 4000 RPM, or 5150 RPM. That’s the variation learn fuel cutoff RPM (depending upon the engine), and that it’s important to release the throttle when the engine RPM starts to decrease as a result of the fuel cutoff going into effect. Failure to do such will result in over revving of the engine, causing possible engine damage.

8. Once the engine has returned to idle, check the status of Diagnostic trouble code P1336. If the scan tool indicates that the CASE has been learned, the relearn procedure is now complete. If CASE has not been learned, check for the presence of other power train codes. If any exist, correct the problem, then repeat this procedure.