Owner's Problem Description
The owner reports that their 1996 Dodge Caravan with a 2.4L engine stalled while driving on December 18 and would not restart. They have replaced the camshaft and crankshaft sensors and checked the relays and coil packs for continuity and resistance. Despite these measures, the engine still does not start. A fault code 33 indicates a short at the A/C clutch relay, prompting concerns about possible underlying issues.
Professional Technical Analysis
This 1996 Dodge Caravan with a 2.4L engine (approximately 180,000 miles) presents a no-start condition following an engine stall. The owner has performed preliminary checks including the replacement of camshaft and crankshaft position sensors, which are critical for ignition timing and fuel injection. Notably, a fault code 33 indicating a short at the A/C clutch relay suggests a potential electrical issue that may be impacting the overall system. Voltage checks at the A/C clutch relay should reveal if a short exists, while testing the PCM for proper operation under load conditions is essential. Given that the vehicle cranks normally but does not start, it's critical to assess spark availability and fuel delivery. The spark plug should be pulled and checked for spark during cranking; this can indicate if the ignition coil or ignition control module (ICM) is malfunctioning. Additionally, testing the fuel pump operation and pressures at the fuel rail is necessary to confirm fuel delivery, ensuring it maintains a pressure of 40-50 PSI. If both spark and fuel are confirmed, further investigation into the PCM and its associated wiring may be warranted. Common failure patterns include wire insulation breakdown or poor ground connections, particularly in older vehicles. Lastly, the condition of the timing belt should be verified to ensure it hasn't skipped a tooth, affecting engine timing.
Possible Causes
Most common causes (ordered by frequency):
- Ignition System Failure: The lack of spark could be due to a faulty ignition control module (ICM) or a failed ignition coil. The ICM in these models is known to fail when it gets hot, leading to no spark conditions. Testing the ICM for proper output voltage during cranking should be performed. Typical resistance values for the coil packs should be between 0.5-1.5 ohms for primary and 7-15 k-ohms for secondary circuits. If the ICM is faulty, replacement is necessary (OEM P/N 56027653). - No spark at the spark plugs, replaced coil pack shows no improvement, potential stored fault codes related to ignition.
- Fuel Delivery Issue: Although the fuel pressure is reported as fine, a clogged fuel filter or a failing fuel pump could prevent adequate fuel delivery to the engine. Fuel pressure should be verified at the rail and should maintain 40-50 PSI. If it drops below this during cranking, further inspection of the fuel pump circuit is necessary. OEM fuel pump replacement cost ranges from $150-250. - Fuel pressure gauge readings during cranking show fluctuating pressure, potential fuel pump noise not audible.
- Electrical Short at A/C Clutch Relay: The fault code 33 indicates a short that could create an electrical issue affecting the PCM's ability to control ignition and fuel injection systems. Inspecting the A/C clutch relay wiring and connections for shorts or corrosion is essential. Repairing or replacing the relay (OEM P/N 4876462AA) may resolve the issue. - Fault code present in the system, visual inspection shows corroded connections at the relay.
- Timing Belt Condition: Although the timing belt appears in place, a skipped tooth could lead to misalignment, causing the engine to lose compression and fail to start. A thorough inspection of the timing belt and associated components (tensioner, idler) should be performed. Timing belt replacement cost is approximately $300-500 including labor. - Visual inspection shows belt in place, but no compression felt at spark plug hole during cranking.
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 OBD-II Scan: Utilize GeekOBD APP or a professional OBD-II scanner to retrieve stored fault codes and freeze frame data. Pay particular attention to the fault code 33, which can provide insight into electrical system integrity. Additionally, check for any other pending codes that may contribute to the no-start condition.
- STEP 2 - Spark and Fuel Verification: Remove a spark plug and check for spark while cranking the engine. If no spark is present, focus on the ignition system components, including the ICM and coil packs. Simultaneously, verify fuel pressure at the fuel rail to ensure it is within the 40-50 PSI range and that the fuel pump is operating correctly.
- STEP 3 - A/C Relay Inspection: Inspect the A/C clutch relay and its wiring for any signs of corrosion or shorts. Use a multimeter to test continuity and resistance across the relay terminals. If necessary, replace the relay (OEM P/N 4876462AA) to eliminate potential electrical issues affecting the PCM and ignition system.
- STEP 4 - Timing Belt Check: Confirm the condition of the timing belt and ensure it has not skipped any teeth. Remove the timing cover if necessary to gain access for visual inspection. If the timing belt is found to be faulty, replace it immediately to restore engine timing and functionality.
