Owner's Problem Description
The owner reports that their 2000 Oldsmobile Alero cranks but won't start. Initially, the car started after following reprogramming instructions for the theft deterrent system. However, after three days, the issue returned despite checking fuel pressure at 40 psi and confirming spark presence. There are no diagnostic trouble codes, and while the vehicle passed emissions, it previously indicated an EVAP system small leak, which was resolved by replacing the gas cap. The owner is unsure of the next steps in diagnosing the problem.
Professional Technical Analysis
The 2000 Oldsmobile Alero is equipped with a 2.4L inline-4 engine and an automatic transmission, with an estimated mileage of 120,000 miles. The vehicle exhibits a 'crank but no start' condition, which can be attributed to several potential issues, particularly in the ignition and fuel systems. Given that the owner confirmed adequate fuel pressure of 40 psi, which falls within the normal operational range of 35-45 psi for this model, and verified the presence of spark, we need to consider additional factors affecting the start condition. The absence of diagnostic trouble codes (DTCs) suggests that the Engine Control Module (ECM) is not detecting any issues within the monitored systems. However, the previous indication of an EVAP leak should prompt an evaluation of the entire fuel system, including the fuel filter which may contribute to fuel delivery issues. It's crucial to note that intermittent issues can arise from faulty electrical connections, particularly involving the ignition system components such as the Ignition Control Module (ICM) or Crankshaft Position Sensor (CPS), which can cause failure to start under certain conditions. Additionally, the theft deterrent system has been implicated in similar cases, although the absence of a security light complicates the diagnosis. Overall, a thorough examination including component testing and live data monitoring via tools like the GeekOBD APP is necessary to isolate the root cause of this no-start condition and ensure all critical systems are functioning correctly.
Possible Causes
Most common causes (ordered by frequency):
- Ignition Control Module (ICM) Failure: The ICM may be experiencing thermal-related failures, particularly in high ambient temperatures, leading to intermittent no-start conditions. This is common in older models, and testing the ICM's signal output during cranking can reveal issues. Typical resistance values for the ICM should be within 500-1500 ohms between terminals. - No security light indication, presence of spark during cranking, common symptoms include intermittent no-start.
- Crankshaft Position Sensor (CPS) Failure: The CPS provides critical timing information to the ECM for ignition and fuel delivery. A failing CPS can cause no-start conditions, particularly if it fails to provide a signal when the engine is cranking. Testing the CPS resistance should yield values within specifications (typically around 200-300 ohms). - Intermittent starting issues, no fault codes stored, signal verification needed during cranking.
- Fuel Filter Clogging: While fuel pressure is adequate, a clogged fuel filter can restrict fuel flow under certain conditions and may not show up as a fault code. Testing the fuel flow rate at the filter and ensuring it meets specifications (typically 1.5-2.5 gallons per hour at key-on) is critical. - Fuel pressure remains stable at 40 psi, yet starting issues persist; flow rate testing needed.
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 - Comprehensive OBD-II Scan: Use GeekOBD APP or a professional OBD-II scanner to perform a detailed scan of the vehicle's systems. Check for stored and pending DTCs, including freeze frame data for further insights into the vehicle's operational state during previous incidents.
- STEP 2 - Live Data Monitoring: Utilize the GeekOBD APP to monitor critical parameters such as fuel pressure, ignition timing, and CPS signal during cranking. Ensure that fuel pressure remains steady at 40 psi, and verify that the CPS is providing a signal during engine cranking. Any deviations may indicate component failures.
- STEP 3 - Component Testing: Individually test the ICM, CPS, and fuel filter based on the live data readings. Check ICM resistance and verify it is within range (500-1500 ohms). Test CPS resistance and inspect for any physical damage. Evaluate fuel filter condition and perform a flow rate test to confirm functionality.
- STEP 4 - Road Test with Data Logging: Conduct a controlled road test while monitoring all relevant parameters through the GeekOBD APP. Document any anomalies in fuel pressure, ignition timing, and engine RPM during the test. This will help isolate the issue further based on real-time data.
