Ensuring your Buick runs smoothly involves maintaining various engine components and systems. One crucial procedure, often necessary after certain repairs or replacements, is the crankshaft variation relearn. This process teaches your Buick’s Powertrain Control Module (PCM) about slight variations in the crankshaft position sensor readings, which is vital for accurate misfire detection and overall engine performance. This guide will walk you through the Buick crankshaft variation relearn procedure using a scan tool, a necessary step to keep your vehicle running at its best.
When is the Crankshaft Variation Relearn Procedure Needed?
The crankshaft position system variation learn procedure is not always required, but it becomes essential under specific circumstances. Performing this relearn procedure is crucial when:
- DTC P1336 is set: This diagnostic trouble code specifically indicates that the PCM has detected an issue with crankshaft position variation learning.
- PCM Replacement: When you replace the PCM, the stored crankshaft variation data is lost, necessitating a relearn.
- Engine Replacement: A new engine might have different crankshaft characteristics, requiring the PCM to learn these variations.
- Crankshaft Replacement: Replacing the crankshaft itself will definitely require a relearn procedure.
- Crankshaft Harmonic Balancer Replacement: Changes to the harmonic balancer can affect crankshaft position readings.
- Crankshaft Position Sensor Replacement: Even with a new sensor, the system needs to relearn to ensure accuracy with the new component.
Prerequisites Before Starting the Procedure
Before you begin the Buick crankshaft variation relearn procedure with your scan tool, ensure the following conditions are met:
- Safety First: Engage the parking brake firmly and block the drive wheels to prevent any unintended vehicle movement during the procedure.
- Engine Warmth: The engine coolant temperature must be at least 70°C (158°F). Allow the engine to run until it reaches this temperature. The scan tool function will be inhibited if the engine is too cold.
- No Active DTCs (Except P1336): Ensure there are no other Diagnostic Trouble Codes (DTCs) present in the powertrain system besides P1336. If other DTCs are present, diagnose and repair them before proceeding. The relearn procedure will be blocked if other DTCs are active.
- Camshaft and Crankshaft Signals: The PCM must not detect any malfunctions in the camshaft position signal circuit, 3X reference circuit, or 18X reference circuit. If your scan tool indicates issues with these signals, refer to the following DTCs for diagnosis:
- Cam Signal Problem: DTC P0341
- 3X Crank Signal Problem: DTC P1374
- 18X Crank Signal Problem: DTC P0336
- Hood Closed: Ensure the vehicle hood is closed for safety and to prevent any interruptions during the procedure.
Step-by-Step Buick Crankshaft Variation Relearn Procedure Using a Scan Tool
Once the prerequisites are confirmed, follow these steps to perform the crankshaft variation relearn procedure using a scan tool:
- Parking Brake and Wheel Blocks: Double-check that the parking brake is set and the drive wheels are securely blocked.
- Warm Up Engine: Start the engine and let it run until the engine coolant temperature reaches at least 70°C (158°F).
- Turn Off Ignition: Turn the ignition OFF.
- Scan Tool Selection: Connect your scan tool to the vehicle’s OBD-II port and navigate to the Crankshaft Position Variation Learn Procedure function in the scan tool menu. Select and enable this function.
- Start Vehicle: Start the engine again.
- Apply Service Brake: Firmly apply and hold the service brake pedal throughout the procedure.
- Transmission in Park: Ensure the transaxle is in the Park position.
- Increase Accelerator Pedal: Gradually depress the accelerator pedal until the engine reaches the CKP system variation learn fuel cut-off point. This fuel cut-off typically occurs around 5150 RPM.
- Release Accelerator: When the engine reaches the second fuel cut-off (you will notice the engine RPM limiting), release the accelerator pedal completely.
- Learning Process: The PCM will now learn the crankshaft position system variation compensating values as the engine RPM decreases back to idle. Avoid touching the accelerator during this phase.
- Procedure Completion: Monitor the scan tool for DTC status, specifically for DTC P1336.
- Verify Completion: If the scan tool indicates that DTC P1336 ran and passed, the Crankshaft Position System Variation Learn Procedure is successfully completed.
- Troubleshooting Failure: If the scan tool indicates DTC P1336 failed or did not run, check for any other DTCs. If no other DTCs are present, repeat the Crankshaft Position System Variation Learn Procedure from step 6. If the procedure continues to fail, consult a repair manual or seek professional diagnostic assistance.
Understanding Fuel Cut-off and RPM
During the relearn procedure, reaching the fuel cut-off RPM is critical. This is a safety feature designed to protect the engine. The first fuel cut-off might be subtle, but the “second fuel cut-off” mentioned in step 9 is more pronounced, indicating the RPM limit for the learn procedure has been reached (around 5150 RPM). Releasing the accelerator pedal at this point allows the PCM to learn the crankshaft variations as the engine speed returns to idle.
Conclusion
The Buick crankshaft variation relearn procedure is a vital step after specific engine repairs or component replacements. Utilizing a scan tool to perform this procedure ensures accurate engine performance and prevents potential misfire issues. By following these steps carefully and ensuring all prerequisites are met, you can successfully complete the relearn process and keep your Buick running smoothly. Remember to always prioritize safety and consult professional resources if you encounter any difficulties.
