And here is GM's relearn procedure, not sure if it's different from what HP Tuners is having you do.DTC P0315
The crankshaft position (CKP) system variation learn feature is used to calculate reference period errors caused by slight tolerance variations in the crankshaft, and the CKP sensor. The calculated error allows the powertrain control module (PCM) to accurately compensate for reference period variations. This enhances the ability of the PCM to detect misfire events over a wide range of engine speed and load. The PCM stores the Crankshaft Position System Variation values after a learn procedure has been performed. If the actual crankshaft position variation is not within the Crankshaft Position System Variation compensating values stored in the PCM, DTC P0300 may set. If the CKP system variation values are not stored in the PCM memory, this DTC sets.
This diagnostic procedure supports the following DTC.
DTC P0315 Crankshaft Position (CKP) System Variation Not Learned
Conditions for Running the DTC
• DTCs P0335, P0336, P0341, P0342, or P0343 are not set.
• The engine coolant temperature (ECT) is more than 70°C (158°F).
Conditions for Setting the DTC
The CKP system variation values are not stored in the PCM memory.
Action Taken When the DTC Sets
• The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.
Conditions for Clearing the MIL/DTC
• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
• Clear the MIL and the DTC with a scan tool.
Did you perform the Diagnostic System Check-Engine Controls?
Yes: Go to Step 2
No: Go to Diagnostic System Check - Engine Controls
Preform the crankshaft position (CKP) system variation learn procedure. Refer to Crankshaft Position System Variation Learn .
Does the scan tool display Learned this ignition?
Yes: Go to Step 4
No: Go to Step 3
If the CKP system variation learn procedure cannot be performed successfully, check for the following conditions and correct as necessary:
• Worn crankshaft main bearings
• A damaged reluctor wheel
• Excessive crankshaft runout
• A damaged crankshaft
• Interference in the signal circuit of the CKP sensor
• Any foreign material passing between the CKP sensor and the reluctor wheel
• A coolant temperature that is not within the Conditions For Running the DTC
• The ignition switch is in the ON position until the battery is drained.
• A PCM power disconnect with the ignition ON may erase the stored value and set the DTC P0315.
Did you complete the inspection?
Yes: Go to Step 4
Clear the DTCs with a scan tool.
Turn OFF the ignition.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Did the DTC fail this ignition?
Yes: Go to Step 2
No: Go to Step 5
Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?
Yes: Go to Diagnostic Trouble Code (DTC) List
No: System OK
Crankshaft Position System Variation Learn
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.
1. Install the scan tool.
2. Apply the parking brake.
3. Block the drive wheels.
4. Close the hood.
5. Place the transmission in Park if the vehicle has an automatic transmission, or in Neutral if the vehicle has a manual transmission.
6. Idle the engine until the engine coolant temperature reaches 65° C (150°F).
7. Turn OFF all of the accessories.
8. Apply the brakes for the duration of the procedure.
Important: If the CKP System Variation Learn Procedure cannot be completed successfully, refer to DTC P0336 for additional diagnostic information.
9. Use the scan tool in order to enable the Crankshaft Position System Variation Learn Procedure.
10. Slowly raise the engine speed to 4,000 RPM.
11. Immediately release the throttle when the engine speed decreases.
12. Turn OFF the ignition for 15 seconds after the learn procedure is completed successfully.