Owner's Problem Description
The owner of a 2002 Mitsubishi Galant is frustrated with a recurring check engine light. The vehicle experienced stalling and has had multiple parts replaced, including the engine module, ignition coils, spark plugs, and both camshaft and crankshaft sensors. After erasing the TPS code, it disappears, but the owner continues to receive a code 44 related to the ignition coil and power transistor unit. Despite inspecting the wiring, the issue persists, causing significant concern and frustration.
Professional Technical Analysis
This 2002 Mitsubishi Galant, equipped with a 2.4L inline-4 engine and an automatic transmission, has approximately 120,000 miles. The owner reports a persistent check engine light alongside stalling issues. The situation worsens after replacing key components such as the engine control module (ECM), ignition coils, spark plugs, and both camshaft and crankshaft sensors. Code 44 indicates a fault in the ignition coil and power transistor unit system, which could stem from several potential causes, including a malfunctioning ignition coil, faulty power transistor, or issues in the wiring harness. A thorough inspection reveals that the wiring appears intact, yet the intermittent nature of the issue suggests possible thermal failure or connection problems that manifest under load or heat. Given the vehicle's age and mileage, wear and environmental factors could contribute to the failure patterns observed, particularly in the ignition system. The check engine light and stalling can also tie back to issues with the throttle position sensor (TPS) and related circuits, as improper readings can lead to fuel delivery problems. It's crucial to monitor the vehicle's performance during operation and upon restart to capture any live data that indicates the root cause of the intermittent stalling and fault code reappearance. The overall vehicle condition warrants immediate attention, especially considering the safety implications of stalling while driving.
Possible Causes
Most common causes (ordered by frequency):
- Faulty Ignition Coil: A malfunctioning ignition coil can lead to inconsistent spark delivery, causing the check engine light to illuminate. In this case, the ignition coil should be tested for primary resistance (0.4-2.0 ohms) and secondary resistance (6,000-12,000 ohms). If either reading is out of spec, replacement is necessary. Additionally, thermal stress can lead to intermittent failure, particularly after prolonged operation. - Check engine light illuminated, stalling under load, testing shows out-of-spec resistance values.
- Power Transistor Failure: The power transistor, which drives the ignition coil, may be failing due to thermal stress or internal circuit damage. This is particularly common in high-mileage vehicles. Testing the transistor for proper operation can be done using a multimeter, checking for appropriate voltage signals during ignition cycles. - Stored code 44, intermittent stalling, visual inspection shows heat damage to the transistor.
- Wiring Harness Issues: Damaged or corroded wiring in the ignition system can interrupt signals between the ECM and ignition components. Inspect the wiring harness for signs of wear, corrosion, or breaks, especially in areas exposed to heat and vibration. - Visual inspection reveals frayed wires, intermittent connectivity issues during testing.
- Thermal Management Failure: High engine temperatures can cause components such as the ignition coil and power transistor to fail. Monitoring engine temperature and ensuring the cooling system is functioning properly can prevent future failures. - Engine overheating indicators, failure to restart after heat soak.
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 - OBD-II Scan: Begin by using a professional OBD-II scanner or the GeekOBD APP to retrieve all stored codes. Pay particular attention to any codes related to the ignition system and TPS. Clear the codes and monitor for reoccurrence during a test drive. Freeze frame data may provide insights into vehicle operation at the time of the fault.
- STEP 2 - Live Data Monitoring: Use the GeekOBD APP to monitor live data from the ignition system, particularly focusing on ignition timing, coil voltage, and TPS readings during acceleration and idle conditions. This can help identify if the TPS is providing incorrect readings that could affect fuel delivery.
- STEP 3 - Component Testing: Conduct resistance tests on the ignition coils and power transistors. For ignition coils, check primary resistance (0.4-2.0 ohms) and secondary resistance (6,000-12,000 ohms). Test the power transistor for proper voltage output during operation. Ensure all connections are secure and free of corrosion.
- STEP 4 - Visual Inspection: Perform a thorough visual inspection of the ignition system wiring and connectors. Look for signs of wear, heat damage, and corrosion. Pay special attention to areas where wires may be exposed to high temperatures or vibrations. Document any irregularities.
