Owner's Problem Description
The owner of a 2003 Pontiac Bonneville reports a persistent P0336 code, indicating a crankshaft position sensor issue. They had the vehicle serviced at George White Pontiac in Ames, IA, where a fuel pump was replaced, and a tune-up was performed. Despite these repairs, the vehicle still struggles to start and the P0336 code remains active. The dealer is unable to diagnose the ongoing issue, prompting the owner to seek further assistance.
Professional Technical Analysis
The 2003 Pontiac Bonneville is likely experiencing issues related to its crankshaft position sensor (CKP) circuit, which is crucial for engine management. The P0336 code indicates that the PCM is not receiving the necessary 18X reference pulses from the CKP sensor. This can be due to a faulty CKP sensor, an open or short circuit in the wiring, or issues with the ignition control module (ICM) connectivity. Given the vehicle's history of having a fuel pump replacement, it's essential to confirm that the fuel delivery system is functioning correctly, as inadequate fuel supply can also affect starting. Moreover, if the dealer performed a tune-up, they should have inspected the ignition system as well. A thorough diagnostic procedure should include checking the CKP sensor's resistance (typically 200-1000 ohms), inspecting the wiring harness for damage or corrosion, and verifying the voltage supply to the sensor (should be approximately 5V). If the CKP sensor is deemed faulty, it should be replaced with an OEM part (P/N 12556118) to ensure compatibility. If wiring issues are detected, proper repairs must be made to restore continuity. The vehicle's current inability to start, combined with the persistent code, suggests a critical need for a systematic approach to diagnosing the CKP system and associated components.
Possible Causes
Most common causes (ordered by frequency):
- Faulty Crankshaft Position Sensor: A malfunctioning CKP sensor may fail to produce the necessary 18X reference pulses, leading to the P0336 code. Testing should confirm the sensor's resistance between 200-1000 ohms and verify the presence of a 5V reference voltage. If faulty, replace with OEM P/N 12556118. - P0336 code, intermittent/no-start condition, CKP sensor resistance out of specifications.
- Wiring or Connector Issues: Damaged or corroded wiring or connectors between the CKP sensor and the PCM can disrupt signal transmission. Inspect the wiring harness for integrity and continuity, focusing on the 12V reference and ground circuits that the CKP sensor shares with the camshaft position sensor. - Visual inspection reveals frayed or corroded wires and loose connectors, intermittent signal loss during testing.
- Ignition Control Module (ICM) Failure: If the ICM is not functioning correctly, it may not relay the signals from the CKP sensor to the PCM effectively. Testing the ICM for proper operation under load conditions is essential. Replace with OEM part if faulty (P/N 10456138). - ICM shows signs of thermal damage, intermittent operation, and failure to provide CKP signals under certain conditions.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - OBD-II Scan: Use a professional OBD-II scanner or the GeekOBD APP to retrieve DTCs and freeze frame data. Pay attention to any related codes that may indicate additional issues. Document the P0336 code and any other active or pending codes.
- STEP 2 - CKP Sensor Testing: Disconnect the CKP sensor connector and measure resistance across the sensor terminals. Resistance should be between 200-1000 ohms. Check the reference voltage at the connector while cranking the engine; it should be around 5V.
- STEP 3 - Wiring Inspection: Inspect the wiring harness for any signs of damage or corrosion, particularly in the areas where the CKP sensor wires run. Check continuity from the CKP connector to the PCM connector to ensure no breaks exist.
- STEP 4 - ICM Testing: If the CKP sensor checks out, proceed to test the ICM. Verify proper operation under load conditions, checking for any abnormalities in signal transmission to the PCM. Replace if necessary.
