Owner's Problem Description
The owner of a 2001 Saturn SL reports intermittent starting issues, where the vehicle will crank but not start. This has occurred twice in the past week after turning off the engine. There are no diagnostic trouble codes (DTCs) stored, and the owner is concerned about a potential underlying issue. The vehicle seems to function normally otherwise.
Professional Technical Analysis
For the 2001 Saturn SL, equipped with a 1.9L I4 engine and an estimated mileage of approximately 120,000 miles, the reported intermittent no-start condition indicates a potential issue with the engine management system. The cranking behavior suggests that the starter motor and battery are functioning properly, as evidenced by the ability to crank the engine. The absence of any stored diagnostic trouble codes (DTCs) complicates the diagnosis, but a systematic approach can be employed to isolate the issue. Notably, the potential causes for this symptom include failure of the crankshaft position sensor (CPS), ignition control module (ICM) malfunction, or fuel delivery issues. The CPS is critical in relaying engine position information to the PCM, and without this signal, the PCM may not trigger the fuel injectors or spark plugs correctly, leading to a no-start condition. In my experience, CPS failures often present without codes, especially in intermittent scenarios where the sensor may function correctly upon cooling down. Additionally, environmental factors, such as temperature fluctuations, can exacerbate sensor failures. Given the vehicle's age and mileage, it's advisable to inspect the CPS wiring harness for corrosion or damage, as well as checking the voltage supply to the ICM which should be approximately 12V during cranking. A thorough check of the fuel system pressure, which should be around 40-50 PSI, would also be warranted if the ignition system is confirmed to be operational.
Possible Causes
Most common causes (ordered by frequency):
- Crankshaft Position Sensor (CPS) failure: A common issue in older Saturn models, the CPS may fail intermittently without triggering a DTC. When the engine is off, it can cool down and function temporarily upon restart, but as it heats up, it may fail to provide the necessary signal to the PCM for fuel and spark operation. Voltage supply to the CPS should be around 5V, and signal output should vary between 0.5V and 4.5V depending on engine position. - No DTCs present, intermittent starting issues, potential loss of signal when hot, CPS voltage readings inconsistent during testing.
- Ignition Control Module (ICM) overheating: The ICM may experience thermal failure due to heat soak from the engine, leading to no spark output during cranking. This condition can occur without any DTCs. Testing should include monitoring the ICM's voltage supply and ensuring it maintains around 12V during cranking. If the ICM is suspected, a replacement (OEM P/N 12595259) may be warranted. - Intermittent spark observed when testing, ICM voltage supply fluctuating, no spark when engine is hot.
- Fuel delivery issues: Insufficient fuel pressure due to a faulty fuel pump or clogged fuel filter can result in a no-start condition. Fuel pressure should be tested with a gauge, ideally maintaining between 40-50 PSI during cranking. If pressure is below this range, further investigation of the fuel pump (OEM P/N 25159872) and filter (OEM P/N 21125091) is necessary. - Fuel pressure gauge readings below 40 PSI, possible signs of fuel starvation during cranking, fuel pump operation noise inconsistent.
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 a professional OBD-II scanner or GeekOBD APP to check for any stored or pending fault codes, even if the check engine light is not illuminated. This step is crucial as it may reveal historical issues that could be contributing to the current problem.
- STEP 2 - Fuel Pressure Test: Connect a fuel pressure gauge to the fuel rail test port. Crank the engine and observe the fuel pressure. It should remain stable between 40-50 PSI. If the pressure is below this range, the fuel pump or filter may need to be checked or replaced.
- STEP 3 - Ignition System Check: Remove two spark plug wires from the ignition coil and crank the engine while observing for spark. If spark is present, check the integrity of the CPS wiring and its voltage output with a multimeter. Confirm the CPS signal output is within the acceptable range of 0.5V to 4.5V.
- STEP 4 - ICM Voltage Check: If no spark is observed, check the voltage supply to the ICM while cranking. It should be around 12V. If the voltage is low or absent, further investigation of the ICM and associated wiring will be necessary.
