Owner's Problem Description
The owner reports that their 2005 Dodge Ram has experienced ignition coil failures, with two coils replaced at different times. After replacing the coils and spark plugs, they still encounter engine codes. The truck runs well, and gas mileage has not changed, but they are seeking further diagnostic advice to resolve the ongoing issue.
Professional Technical Analysis
The 2005 Dodge Ram with a typical HEMI engine has been experiencing issues related to ignition coils, which are critical for proper engine operation. The vehicle has been driven extensively, likely exceeding 150,000 miles, and intermittent stalling or misfires may occur due to faulty ignition components. Given the history of previous coil failures, it's essential to check not only the coils but also the wiring harness and PCM (Powertrain Control Module) for potential issues. The owner has measured the resistance on the coil wires, noting significant discrepancies: #2 cylinder at 1.34 kΩ and #7 cylinder at 574 Ω, while other coils measure around 2.55 MΩ. Such inconsistencies can indicate wiring issues or PCM-related failures. A thorough inspection should include checking the integrity of the coil connectors, ensuring there are no shorts or opens in the harness, as Chrysler has acknowledged issues with the ignition coil harness in these models. Warning lights, including the check engine light, may illuminate due to misfires detected by the PCM, which can store fault codes relevant to the ignition system. In this case, codes related to misfires (P0300-P0308) are likely. The current condition of the vehicle suggests it runs well, but the need for a detailed examination of the ignition system is critical for reliability and safety. Electrical tests should include checking for proper voltage supply (12V) to the coils during operation and ensuring ground connections are intact. Given the age of the vehicle, previous repairs may also provide clues to latent issues, and the history of ignition coil replacements indicates that further diagnostics are warranted to prevent future failures.
Possible Causes
Most common causes (ordered by frequency):
- Ignition Coil Failure: The previous replacement of ignition coils suggests a recurring issue. Measurements indicate #2 cylinder at 1.34 kΩ and #7 cylinder at 574 Ω; these values are abnormal, as healthy coils should exhibit similar resistance values around 0.5-1.5 ohms. This inconsistency can lead to misfires and subsequent engine codes. Ignition coils typically fail due to heat, vibration, and electrical overload. It's critical to verify if the coils have been properly installed and that the connectors are clean and secure. - Check engine light illumination, recorded misfire codes, fluctuating voltages during operation indicating potential coil or harness issues.
- Wiring Harness Issues: Chrysler has acknowledged problems with the ignition coil wiring harness on some models. Corrosion, wear, or poor connections can lead to increased resistance or open circuits, resulting in intermittent coil operation. Testing for voltage drop across the wiring harness and inspecting connectors for signs of wear or damage is crucial. Repair or replacement of the harness may be necessary if issues are found. - Visual inspection of wiring harness shows no obvious damage, but intermittent faults may not be visible. Voltage drop across connectors should be less than 0.2V.
- PCM Malfunction: If the PCM fails, it can lead to incorrect signals sent to the ignition coils, resulting in misfires and diagnostic trouble codes. Testing the PCM for proper operation and ensuring it is receiving accurate input signals from sensors is vital. If the PCM is determined to be faulty, it will need to be replaced by a professional due to security programming concerns. - Stored fault codes related to ignition system, abnormal readings from sensors detected by PCM, potential signs of overheating.
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: Begin with a detailed scan using an OBD-II scanner or GeekOBD APP to retrieve stored trouble codes and freeze frame data. This initial step will help identify any misfire codes (P0300-P0308) and provide insights into fuel trim and other relevant parameters during the vehicle's operation.
- STEP 2 - Electrical Testing: Using a multimeter, measure the resistance of the ignition coils' primary and secondary windings. For primary tests, expect around 0.5-1.5 ohms, and for secondary tests, approximately 6,000-12,000 ohms. Additionally, check for voltage at the coil connectors during cranking; there should be a stable 12V. Document any deviations from these specifications.
- STEP 3 - Wiring Harness Inspection: Carefully inspect the ignition coil wiring harness for signs of wear, corrosion, or damage. Pay attention to the connectors and ensure they are clean and securely connected. If corrosion is found, clean the connectors and apply dielectric grease to prevent future issues. Consider performing a voltage drop test across the harness during operation.
- STEP 4 - PCM Functionality Test: If all previous checks are satisfactory and issues persist, test the PCM for proper operation. This may involve using a professional scan tool to check for consistent sensor inputs and outputs. If the PCM is suspected to be faulty, it should be taken to a specialist for further diagnosis and potential replacement.
