OBD2 Scanner with Relearn: Performing a Crankshaft Position Relearn

Performing a Crankshaft Position (CKP) relearn, sometimes referred to as CASE relearn, is a crucial procedure after certain automotive repairs or component replacements. This process ensures the engine control module (ECM) accurately reads the crankshaft position sensor signal, which is vital for proper engine timing and performance. While specific steps can vary depending on the vehicle and scan tool, understanding the general prerequisites and procedure is essential for any automotive technician. This guide outlines the key factors to consider when performing a CKP relearn using an OBD2 scanner.

Essential Prerequisites Before Starting a CKP Relearn

Before initiating the CKP relearn procedure with your OBD2 scanner, several conditions must be met to ensure successful completion. Failure to address these prerequisites can result in the relearn process failing to run, potentially leading to continued engine performance issues or the inability to start the vehicle.

Firstly, it is imperative that no relevant Diagnostic Trouble Codes (DTCs) are present. Specifically, the following codes must be resolved before attempting a CKP relearn:

• P0335 Crankshaft Position (CKP) Sensor A Circuit
• P0336 Crankshaft Position (CKP) Sensor A Performance
• P0341 Camshaft Position (CMP) Sensor Performance Bank 1 Sensor A
• P0342 Camshaft Position (CMP) Sensor Circuit Low Bank 1 Sensor A
• P0343 Camshaft Position (CMP) Sensor Circuit High Bank 1 Sensor A
• P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low
• P0118 Engine Coolant Temperature (ECT) Sensor Circuit High
• P1539 Air Conditioning (A/C) Clutch Feedback Circuit High Voltage
• P1546 Air Conditioning (A/C) Clutch Feedback Circuit Open
• P0705 Transmission Range (TR) Switch Circuit
• P0706 Transmission Range (TR) Switch Performance
• P1810 Transmission Fluid Pressure (TFP) Position Switch Circuit
• P1825 Internal Mode Switch-Invalid Range

These DTCs indicate potential issues with the crankshaft position sensor circuit, camshaft position sensor, engine coolant temperature sensor, transmission range switch, or other related systems. Addressing these faults is crucial as they can directly interfere with the relearn process and indicate underlying mechanical or electrical problems.

Secondly, several operating conditions must be within specified ranges:

• Engine Coolant Temperature (ECT): Must be between 150°F and 220°F (65°C – 104°C). This ensures the engine is at a proper operating temperature for the procedure.
• Engine RPM: Must be below 2400 RPM before starting the procedure. This is a safety precaution and ensures the engine is idling or at a low speed.
• Throttle Position Sensor (TPS): Must read 0%. This indicates the throttle is fully closed, a necessary condition for accurate relearn.
• Vehicle Speed Sensor (VSS): Must read 0 mph. The vehicle must be stationary for the procedure.

Finally, ensure the following vehicle conditions are met:

• Parking Brake: Engaged for safety.
• Transmission: In Park or Neutral.
• Accessories: Turn off all unnecessary accessories (A/C, headlights, radio, etc.) to minimize electrical load.
• Brake Pedal: Keep foot firmly on the brake pedal throughout the procedure unless instructed otherwise by your OBD2 scanner.

Step-by-Step CKP Relearn Procedure with an OBD2 Scanner

While the exact menu navigation may differ slightly depending on your specific OBD2 scanner make and model, the general steps for performing a CKP relearn are as follows:

1. Connect your OBD2 scanner to the vehicle’s diagnostic port.

2. Power on the scanner and navigate to the Diagnostic or Service menu.

3. Select the Powertrain Control Module (PCM) or Engine Control Module (ECM) for diagnostics.

4. Look for special functions, module programming, or service procedures.

5. Find and select the CKP Relearn, Crankshaft Relearn, CASE Relearn, or similar function. The terminology may vary.

6. Follow the on-screen prompts provided by your OBD2 scanner. These prompts will guide you through the specific actions required. Typically, this involves:

   • Starting the engine if instructed.
   • Increasing engine RPM to a specified level (usually above 4000 RPM) within a short timeframe (e.g., 10 seconds) when prompted.
   • Quickly releasing the throttle when you hear or feel a stumble or misfire. This indicates the ECM has successfully learned the crankshaft position.
   • Allowing the engine to return to idle.
   • Turning off the engine and waiting for a specified period (e.g., 15 seconds) before deactivating the relearn function on the scanner.

7. After completing the procedure as instructed by your scanner, deactivate the relearn function on the OBD2 scanner.

8. Disconnect the scanner from the vehicle.

9. Start the engine and verify that the engine runs smoothly and that no DTCs related to crankshaft or camshaft position sensors are present.

Successfully performing a CKP relearn with an OBD2 scanner is essential after replacing a crankshaft position sensor, ECM, or performing engine work that could affect crankshaft position sensor readings. By following these prerequisites and procedural steps, you can ensure accurate engine operation and optimal vehicle performance. Always consult your vehicle’s service manual and your OBD2 scanner’s user guide for specific instructions and recommendations.