Owner's Problem Description
The owner's 2002 Saturn L200 has started stalling while driving on the highway. This issue first occurred when the owner's wife was driving on the interstate. After stalling, the vehicle was towed to a Buick dealership where diagnostics revealed no issues. However, the problem recurred later that night, with the vehicle stalling multiple times during a subsequent drive. It would restart after a waiting period but eventually stalled again and was towed to a Saturn dealership, where the problem remains unresolved.
Professional Technical Analysis
The 2002 Saturn L200 is equipped with a 2.2L inline-4 engine and an automatic transmission, typically averaging around 120,000 miles. The owner reports intermittent stalling while driving, particularly at highway speeds. Symptoms include abrupt engine shutdowns, with the vehicle requiring a waiting period before it can be restarted. The dealership's diagnostic tests have shown no faults in the fuel system pressure or charging system, which suggests possible issues with ignition components or sensor failures. A thorough review of interconnections is necessary: the PCM controls fuel delivery based on inputs from the crankshaft position sensor (CPS) and ignition control module (ICM). If the CPS fails while the engine is hot, it can lead to stalling as the PCM may not receive necessary timing signals. The ICM may also exhibit thermal failure, particularly under prolonged highway driving conditions, which is common in this model. With reported instances of stalling, it is vital to monitor both fuel pressure and spark during stall events. The normal fuel pressure for the fuel system should be 41-47 PSI. An oscilloscope can be used to check the ignition signal integrity. Current vehicle condition indicates that stalling poses a safety risk, particularly in high-speed conditions, and could lead to accidents if not addressed promptly.
Possible Causes
Most common causes (ordered by frequency):
- Crankshaft Position Sensor (CPS) failure: The CPS is critical for providing accurate position data to the PCM. If the CPS fails intermittently, especially when hot, the PCM may not receive the necessary signals, causing stalling. The CPS should have a resistance value of 200-800 ohms; testing should be done when the engine is at operating temperature. Common failures are observed after 80,000 miles, particularly in high-heat environments. - Engine stalling at highway speeds, troubleshooting revealing no fuel pressure issues, CPS resistance readings out of specification when hot.
- Ignition Control Module (ICM) thermal failure: The ICM may fail when exposed to high temperatures, interrupting the ignition signal. This failure often manifests after prolonged driving at high speeds, where the engine bay temperature exceeds 200°F. A failed ICM can lead to loss of spark, causing the engine to stall. Testing the ICM should include checking for proper resistance values (1-5 ohms) and signal output during operation. - Symptoms of stalling, particularly after long drives, ICM testing shows intermittent output under high temperatures, which can lead to no-start conditions.
- Fuel System Issues: Despite initial tests indicating normal fuel pressure, intermittent issues can arise from the fuel pump relay or wiring that becomes compromised under heat and vibration. The fuel pressure should be verified (41-47 PSI) during stall conditions. The fuel pump should provide adequate flow (minimum 30 PSI) and should be tested under load with a pressure gauge. - Intermittent stalling, pressure gauge shows fluctuations during operation, wiring harness inspection reveals wear or damage.
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 - Initial OBD-II Scan: Utilize the GeekOBD APP for a comprehensive OBD-II scan to retrieve any stored codes. Pay close attention to any pending codes related to the ignition system or CPS. Freeze frame data can provide context regarding engine conditions when stalling occurs.
- STEP 2 - Monitor Live Data: Use the GeekOBD APP to monitor live data including fuel pressure readings and ignition signals during driving. Specifically, check the fuel pressure while the vehicle is under load; it should remain stable between 41-47 PSI. Additionally, observe the ignition timing and any fluctuations in the ICM signal.
- STEP 3 - Component Testing: Conduct targeted tests on the CPS and ICM based on the data collected. Check the resistance of the CPS (should be 200-800 ohms) and measure the ICM’s output signal using an oscilloscope to ensure it is functioning under normal conditions.
- STEP 4 - Road Test: Perform a controlled road test while monitoring parameters through the GeekOBD APP. Document any instances of stalling and correlate them with data collected, particularly focusing on fuel pressure and ignition signal integrity during these events.
