Owner's Problem Description
The owner reports that their 1999 Dodge Intrepid engine stops unexpectedly while driving. It shuts off without warning, and after replacing the ASD relay with a fan relay, the vehicle still runs only a short distance before shutting down. Previous repairs include crank sensor replacement. The engine will start again but may shut down soon after, with flickering interior lights observed during the last stall. The owner is considering the ECM as a potential issue but seeks further diagnostic input.
Professional Technical Analysis
The 1999 Dodge Intrepid, equipped with a 3.5L V6 engine and approximately 120,000 miles, presents an intermittent engine shutdown issue. The symptoms include unexpected engine stalling while driving, with the interior lights flickering during the last incident. The ASD relay was replaced, and the crankshaft position sensor was also changed, but the problem persists. This situation suggests potential issues with the powertrain control module (PCM), electrical connections, or fuel delivery system. Voltage readings from the charging system should be checked, ensuring stable levels of 13.8-14.4V under load. Additionally, the crank sensor must maintain proper resistance values (typically around 500-1500 ohms). If the PCM is faulty, it can lead to erratic operation of the fuel pump and ignition system, resulting in the engine stalling. This vehicle's history of intermittent electrical issues often points towards grounding problems or failing relays. A thorough inspection of all related connectors and grounds is critical, as is testing for stored trouble codes using an OBD-II scanner. The GeekOBD APP can be particularly useful for real-time monitoring during road tests to identify any voltage drops or signal disruptions that correlate with the engine shutdown events.
Possible Causes
Most common causes (ordered by frequency):
- PCM Failure: The powertrain control module may be failing intermittently, causing the engine to shut off without warning. This can be due to internal faults or issues with the vehicle's wiring harness. A common symptom is the flickering of dashboard lights before the engine stalls, indicating potential voltage fluctuations. Checking for stored trouble codes is essential, as they may point to specific failures. Voltage readings should be stable (13.8-14.4V) during operation; any deviations could indicate PCM issues. Testing the PCM with a known good unit can confirm its functionality. - Dashboard lights flickering prior to stalling, recent repairs to ASD relay and crank sensor, potential stored codes indicating PCM failure.
- Wiring Issues: Corrosion or loose connections in the wiring harness can lead to intermittent electrical failures. This could cause the PCM to lose communication with the ignition system or fuel pump, resulting in an unexpected engine shut-off. A visual inspection of the wiring for frays, corrosion, or broken connectors is crucial. Testing continuity and resistance in all related circuits should also be performed. GeekOBD APP can assist in monitoring voltage drops when the vehicle is running to help pinpoint any wiring issues. - Visual inspection reveals frayed wiring or loose connections, potential voltage drops observed during operation, and intermittent connectivity issues.
- Fuel Delivery Problems: A failing fuel pump or clogged fuel filter can lead to insufficient fuel supply, causing the engine to stall. Monitor fuel pressure, which should be between 35-45 PSI at idle. If the fuel pressure is below this range, it indicates a potential issue with the fuel pump or filter. Testing the fuel pressure at the rail and inspecting the fuel filter for clogs is necessary. If the pump is suspected, it should be checked for proper operation and voltage supply (typically 12V). - Fuel pressure readings below 35 PSI, signs of a clogged fuel filter, and intermittent fuel pump operation.
- Ignition System Malfunction: Issues with the ignition coil or the crankshaft position sensor can lead to erratic spark generation, resulting in engine stalling. The crank sensor must be tested for proper voltage and resistance (500-1500 ohms). If the ignition coil is failing, it may show signs of overheating or inconsistent output. Checking the ignition system components for proper operation and signal integrity is vital. Use the GeekOBD APP to monitor the ignition timing and any stored codes related to the ignition system. - Fluctuating ignition timing readings, potential stored codes indicating ignition system failures, and faulty ignition coil operation.
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 Code Retrieval: Begin with a thorough OBD-II scan using the GeekOBD APP to retrieve any stored fault codes. This step is crucial as it can provide insight into the PCM and other system failures. After the initial scan, check for any freeze frame data that may indicate the conditions under which the fault occurred. This information is vital for diagnosing the root cause of the engine stalling issue.
- STEP 2 - Live Data Monitoring: Use the GeekOBD APP to monitor live data parameters, focusing on fuel pressure, ignition timing, and voltage levels. Fuel pressure should be maintained between 35-45 PSI, and ignition timing must remain consistent. Document any anomalies during operation, especially when the engine is about to stall. This data will help narrow down potential causes.
- STEP 3 - Component Inspection and Testing: Inspect the wiring harness for any signs of corrosion or damage that could affect electrical connections. Test the crankshaft position sensor for proper resistance and voltage output. Additionally, check the fuel pump operation by testing fuel pressure at the rail. Use the GeekOBD APP to monitor the sensor signals and ensure they are within specification.
- STEP 4 - Road Testing and Verification: Conduct a controlled road test while monitoring the vehicle's performance with the GeekOBD APP. Pay close attention to any fluctuations in voltage, fuel pressure, and ignition timing during operation. Document any occurrences of stalling and correlate them with the data collected. This will help in verifying the effectiveness of any repairs made.
