Owner's Problem Description
The owner of a 1996 Chrysler Cirrus reports that the 20 amp fuse for the ignition and fuel starter keeps blowing. They received the car in March and haven't changed the fuel filter since. To temporarily fix the issue, they wrapped a wire around the fuse, allowing the car to start and run well. The owner is now considering whether to use a higher-rated fuse and is seeking advice on the situation.
Professional Technical Analysis
The 1996 Chrysler Cirrus, equipped with a 2.4L inline-4 engine and an automatic transmission, likely has around 150,000 miles on the odometer. The reported issue of the 20 amp fuse blowing repeatedly indicates a potential short circuit or overload in the ignition and fuel supply circuits. The fuse in question is responsible for providing power to the Automatic Shutdown (ASD) relay, which in turn supplies voltage to critical components such as the fuel injectors, ignition system, and oxygen sensor heaters. A crucial step in diagnosing this issue is to verify the integrity of the wiring and connections leading to these components. Given the owner's temporary fix of wrapping a wire around the fuse, which is not a safe or recommended practice, the risk of fire or further electrical damage is heightened. Environmental factors such as moisture, corrosion, or rodent damage could also contribute to the fault. Systematically, the next steps should include inspecting the wiring harness for any visible damage or shorts, checking the fuel pump relay functionality, and testing the resistance of the components powered by the ASD relay. If the oxygen sensors are suspected, disconnecting them temporarily to see if the fuse still blows can help isolate the source of the problem. Furthermore, running a diagnostic scan for any stored trouble codes may provide additional insights into the malfunctioning components. Given the vehicle's mileage, it would also be prudent to check the fuel filter, as a clogged filter could cause excessive load on the fuel pump, potentially leading to fuse failure due to overcurrent conditions.
Possible Causes
Most common causes (ordered by frequency):
- Short Circuit in Wiring Harness: Inspect the wiring harness for signs of abrasion or damage that could cause a short circuit, particularly in areas where the harness passes through tight spaces or near heat sources. A resistance test should be performed on the wiring from the ASD relay to the components it powers, expecting near zero ohms in good condition. Any significant deviation indicates a fault. - Visible frayed wires, melting insulation, and burnt connectors found during inspection.
- Faulty Fuel Pump Relay: A malfunctioning fuel pump relay can lead to excessive current draw, causing the 20 amp fuse to blow. Testing the relay with a multimeter for proper operation (typically around 75 ohms coil resistance) is essential. If the relay fails to activate or shows abnormal resistance, it should be replaced. - Relay clicks but does not power the fuel pump, and resistance measurements are outside normal parameters.
- Overloaded Circuit from Faulty Components: If any of the components powered by the ASD relay (like the fuel injectors or ignition system) are malfunctioning, they may draw excessive current, leading to fuse failure. Each component should be tested for proper operation and resistance, with injectors typically showing around 12-16 ohms resistance. - Fuel injectors not firing correctly, with resistance measurements indicating values outside the normal range.
- Defective Oxygen Sensors: Oxygen sensors can short internally, causing excessive current draw and blowing the fuse. Disconnecting the oxygen sensors to see if the fuse still blows is a quick test to confirm this possibility. The normal resistance for heated oxygen sensors should be around 10-20 ohms. - Oxygen sensor codes stored, and disconnection led to fuse remaining intact.
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 - Visual Inspection: Begin with a thorough visual inspection of the under-hood wiring harness, connectors, and fuses. Look for any signs of fraying, corrosion, or heat damage. Pay special attention to areas where wires may rub against metal or become pinched. This step can reveal visible issues that may contribute to the ongoing fuse failure.
- STEP 2 - Relay Testing: Next, test the fuel pump relay using a multimeter to confirm its operation. Measure the coil resistance and ensure it falls within the expected range (typically around 75 ohms). If the relay does not activate properly, replace it with an OEM part (e.g., OEM P/N 4676290AA).
- STEP 3 - Component Resistance Testing: Test the resistance of the fuel injectors and oxygen sensors to ensure they are operating within specifications. Fuel injectors should typically show around 12-16 ohms, while oxygen sensors should be around 10-20 ohms. Any deviations indicate a component fault that needs to be addressed.
- STEP 4 - Circuit Load Testing: If no faults are found, perform a load test on the ignition and fuel systems. This can be done by using a multimeter to measure the current draw while the engine is cranking and running. This will help identify if any component is drawing excessive current and causing the fuse to blow.
