Owner's Problem Description
The owner of a 2006 Pontiac Grand Prix reports that the vehicle suddenly dies without warning while driving. The engine cranks but does not start after the stall. This has happened multiple times since January 2011, with instances of the vehicle restarting after a short period. Previous diagnostics at a GM dealer showed no codes, and a fuel pump replacement was suggested but not performed. The vehicle is currently exhibiting the same symptoms again.
Professional Technical Analysis
The 2006 Pontiac Grand Prix with an approximate mileage of around 100,000 miles is experiencing intermittent stalling issues that result in no-start conditions. Symptoms have been observed primarily after the vehicle has been parked for extended periods (8 hours or more) and typically occur within the first few miles of driving. Initial diagnostics performed by a dealer yielded no fault codes, indicating a potential intermittent fault that could be linked to components such as the crankshaft position sensor or fuel delivery system. Given the nature of the symptoms, a thorough analysis of the ignition and fuel systems is essential. It is critical to monitor the fuel pressure, which should maintain at 35-45 PSI during operation, and check for spark during the no-start condition. The crankshaft position sensor, which is known to cause stalling by cutting spark when it fails, should also be tested as it may not throw a code during intermittent failure. Current vehicle condition is concerning, as safety could be compromised during stalling events in traffic. Further investigation into the electrical connections, particularly under the hood, is warranted due to potential heat-related failures. Historical context suggests a common failure of the crankshaft position sensor in similar models around this mileage, which could lead to the symptoms exhibited by the vehicle.
Possible Causes
Most common causes (ordered by frequency):
- Crankshaft Position Sensor Failure: The crankshaft position sensor (part number 12558690) is known to fail intermittently, leading to a lack of spark when the engine is cranking. This sensor is crucial for the operation of the ignition system and is typically located at the lower part of the engine block. Symptoms often manifest after the vehicle has been parked for long periods when heat buildup has occurred. Testing should show an open circuit or inconsistent resistance values under heat conditions. - No spark during cranking, intermittent failure when hot, potential stored codes P0335-P0338 related to crankshaft position sensor.
- Fuel Pump Intermittent Failure: Although previous checks indicated normal fuel pressure, the fuel pump (part number 19207347) may still be failing intermittently due to internal wear or electrical issues. A drop in fuel pressure during cranking can lead to no-start conditions. Fuel pumps tend to fail after prolonged use, particularly around the 100,000-mile mark. Conducting a fuel pressure test during a no-start condition is critical. - Intermittent no-start condition, previous tests showed good pressure, potential for overheating or electrical connector issues.
- Electrical Connection Issues: Poor electrical connections, especially at the ignition coil or fuel pump relay, can cause intermittent no-start conditions. Corrosion, loose connectors, or broken wires can lead to voltage drops. Testing should include checking the integrity of connections and voltage at the fuel pump relay (should be 12V when the ignition is on). - Visual inspection of connectors shows signs of corrosion, intermittent voltage readings during testing.
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 No-Start Diagnosis: When the vehicle experiences a no-start condition, immediately check for spark and fuel pressure. Use a spark tester to verify the presence of spark from the ignition coil. Concurrently, connect a fuel pressure gauge to the fuel rail to ensure the pressure is within the 35-45 PSI range. If fuel pressure is low, investigate the fuel pump and its electrical connections.
- STEP 2 - Crankshaft Position Sensor Testing: If no spark is detected, test the crankshaft position sensor using a multimeter. The resistance should typically be between 200-800 ohms. If the sensor reads open circuit or has inconsistent resistance, it indicates a failure. Replace if necessary with OEM part number 12558690.
- STEP 3 - Fuel Pump Electrical Testing: Conduct a voltage test at the fuel pump relay while cranking the engine. The voltage should read 12V. If it does not, trace the wiring back to the ignition switch and check for continuity and any signs of damage. Repair or replace faulty wiring as necessary.
- STEP 4 - Visual Inspection of Electrical Connections: Inspect all electrical connections related to the ignition system and fuel pump for corrosion, looseness, or damage. Clean and secure any connections as necessary to ensure optimal electrical conductivity.
