Crankshaft Variation Relearn Procedure: Step-by-Step Guide with Scan Tool

Performing a crankshaft variation relearn procedure, sometimes referred to as a CASE relearn, is essential for ensuring the accurate operation of your vehicle’s engine control system. This procedure is particularly crucial after replacing the crankshaft position sensor, the engine control module (ECM), or when engine work has been performed that could affect crankshaft position readings. Using a scan tool to execute this relearn process is the most efficient and accurate method. This guide outlines the necessary preconditions and steps to successfully complete a crankshaft variation relearn using a scan tool, ensuring optimal engine performance.

Before initiating the crankshaft variation relearn procedure with your scan tool, several conditions must be met to guarantee a successful outcome. Failure to adhere to these preconditions can prevent the procedure from running correctly, leading to frustration and potential diagnostic errors. Ensure that none of the following Diagnostic Trouble Codes (DTCs) are present, as these can directly interfere with the relearn process:

• P0335 Crankshaft Position (CKP) Sensor A Circuit: Indicates a problem with the CKP sensor circuit itself.
• P0336 Crankshaft Position (CKP) Sensor A Performance: Signals that the CKP sensor is not performing within expected parameters.
• P0341 Camshaft Position (CMP) Sensor Performance Bank 1 Sensor A: Indicates a performance issue with the camshaft position sensor, which can affect the crankshaft relearn.
• P0342 Camshaft Position (CMP) Sensor Circuit Low Bank 1 Sensor A: Signifies a low voltage condition in the camshaft position sensor circuit.
• P0343 Camshaft Position (CMP) Sensor Circuit High Bank 1 Sensor A: Indicates a high voltage condition in the camshaft position sensor circuit.
• P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low: A low reading from the ECT sensor can prevent the procedure from starting.
• P0118 Engine Coolant Temperature (ECT) Sensor Circuit High: A high reading from the ECT sensor can also halt the relearn process.
• P1539 Air Conditioning (A/C) Clutch Feedback Circuit High Voltage: An issue with the A/C clutch feedback circuit can sometimes interfere.
• P1546 Air Conditioning (A/C) Clutch Feedback Circuit Open: Similarly, an open circuit in the A/C clutch feedback can cause problems.
• P0705 Transmission Range (TR) Switch Circuit: Problems with the transmission range switch circuit can affect engine control processes.
• P0706 Transmission Range (TR) Switch Performance: Performance issues with the transmission range switch can also interfere.
• P1810 Transmission Fluid Pressure (TFP) Position Switch Circuit: Faults in the transmission fluid pressure position switch circuit can be problematic.
• P1825 Internal Mode Switch-Invalid Range: An invalid range detected by the internal mode switch can prevent the relearn.

In addition to the absence of these DTCs, the following engine and vehicle conditions must be met before commencing the crankshaft variation relearn procedure with a scan tool:

• Engine Coolant Temperature (ECT): The engine coolant temperature must be within the range of 150°F to 220°F (65°C to 104°C). This ensures the engine is at a proper operating temperature for the procedure.
• Engine RPM: The engine speed must be below 2400 RPM before starting the procedure. This is a safety precaution and ensures accurate data collection during the relearn.
• Throttle Position Sensor (TPS): The throttle position sensor reading must be at 0%, indicating a closed throttle position or idle.
• Vehicle Speed Sensor (VSS): The vehicle speed sensor must read 0 mph, meaning the vehicle must be stationary.

Furthermore, ensure the following vehicle setup conditions are in place:

• Parking Brake: Apply the parking brake firmly to prevent any vehicle movement during the procedure.
• Transmission Position: Place the transmission in Park (for automatic transmissions) or Neutral (for manual transmissions).
• Accessories: Turn off all unnecessary accessories such as headlights, radio, and air conditioning to minimize electrical load on the system during the procedure.
• Brake Pedal: Keep your foot firmly pressed on the brake pedal throughout the initial steps of the procedure as a safety measure.

Once all the preconditions are verified and met, proceed with the following steps to perform the crankshaft variation relearn procedure using your scan tool:

1. Connect Scan Tool: Connect your scan tool to the vehicle’s diagnostic port. Initiate communication by clicking the “connect” or equivalent button on your scan tool interface.

2. Navigate to DVT Tab: Within your scan tool software, navigate to the “DVT” (Diagnostic Test) tab or the section that allows for module-specific tests and procedures.

3. Select Controller: Choose the appropriate controller from the list, typically this will be the “Engine Control Module (ECM)” or Powertrain Control Module (PCM).

4. Activate Procedure: Look for an “Activate” or “Start” button or option within the ECM/PCM functions. Click this to access the available procedures.

5. Go to Learning Subtab: Within the activated functions, find a “Learning” subtab or a similar section that houses relearn procedures.

6. Initiate CASE Learn: Locate and select the “CASE” or “Crankshaft Position System Variation Learn” option. This may be labeled differently depending on your scan tool manufacturer, but it will generally be clear in its description. Click to initiate the procedure.

7. Increase RPM: As prompted by the scan tool, smoothly and rapidly open the throttle to increase the engine RPM above 4000 RPM within 10 seconds. It’s crucial to reach this RPM threshold quickly for the procedure to register correctly.

8. Release Throttle Upon Stumble: Carefully listen and feel for the engine to stumble or misfire. This stumble indicates that the relearn procedure is registering the crankshaft variation. Immediately release the throttle as soon as you detect this stumble.

9. Engine Spindown to Idle: Allow the engine to naturally spindown and return to its idle RPM. Do not interfere with the throttle during this spindown process.

10. Turn Off Engine and Wait: Once the engine has returned to idle, turn off the engine completely and wait for 15 seconds. This allows the ECM/PCM to finalize the learned crankshaft variation data.

11. Deactivate Scan Tool (Optional): While waiting the 15 seconds after engine shutdown, you can optionally click “Deactivate” or disconnect from the controller within your scan tool software. This step is not always necessary but is good practice.

By following these preconditions and steps diligently, you can effectively perform a crankshaft variation relearn procedure using a scan tool. This ensures the engine control system accurately interprets crankshaft position, contributing to optimal engine performance and preventing potential drivability issues.