Owner's Problem Description
The owner reports that the anti-theft light on their 2006 Chrysler PT Cruiser occasionally flashes, which coincides with the vehicle not starting. They specifically noted that they couldn't hear the fuel pump priming when attempting to start the car. Additionally, the check engine light is illuminated, and multiple fault codes (P1603, P700, P882, P218, P714, U101) are present. The owner has conducted some troubleshooting but suspects a problem with the computer system.
Professional Technical Analysis
This 2006 Chrysler PT Cruiser, equipped with a 2.4L inline-4 engine and an automatic transmission, has an estimated mileage of around 120,000 miles. The intermittent flashing of the anti-theft light, accompanied by a no-start condition and the absence of fuel pump priming, suggests a potential issue with the vehicle's security system or PCM (Powertrain Control Module). The presence of multiple fault codes, particularly P1603 which indicates a PCM internal fault, likely points to an electrical communication issue within the PCM. The P700 code pertains to transmission control, indicating a possible communication failure between the PCM and transmission control module. Codes P882 and U101 denote issues with network communication, further supporting the likelihood of a PCM-related failure. The condition of the battery and connections must be verified, as a weak battery can cause erratic PCM behavior. Given that the vehicle has been experiencing these symptoms, it is critical to check the integrity of the wiring harness and connectors related to the PCM and TCM (Transmission Control Module). A comprehensive OBD-II scan using a professional tool or the GeekOBD APP would be essential to capture live data and analyze the behavior of the fuel pump and PCM under various conditions. The current vehicle condition raises safety concerns, particularly if the no-start condition occurs in a hazardous situation, warranting immediate attention. Preliminary observations should include checking the battery voltage (should be above 12.4V), verifying the fuel pump relay operation, and ensuring that the PCM is receiving proper inputs from the ignition switch and crankshaft position sensor.
Possible Causes
Most common causes (ordered by frequency):
- PCM Internal Fault (P1603): The Powertrain Control Module may have internal circuitry issues that cause it to fail to communicate properly with other systems. This can result in no-start conditions and trigger anti-theft system features, such as the flashing light. In cases where the PCM fails, it's often necessary to replace it with an OEM unit (OEM P/N 56044550AE) and reprogram it to match the vehicle's specifications. A thorough electrical inspection should be performed to rule out external shorts or poor connections that could lead to this fault. - Multiple fault codes indicating communication issues, no fuel pump activation, and intermittent starting problems.
- Fuel Pump Relay Failure: The fuel pump relay may be malfunctioning, preventing the fuel pump from priming when the ignition is turned on. This could lead to a no-start condition. Testing the relay should include checking for proper resistance (typically 70-80 ohms) and ensuring that the relay receives adequate voltage from the PCM when energized. If the relay fails, replacement (OEM P/N 5016980AA) is necessary. - No sound from fuel pump during ignition, relay not clicking, and fault codes related to fuel delivery.
- Wiring Issues: Damage or corrosion in the wiring harness connecting the PCM to the fuel pump and other critical components can lead to communication failures and prevent the fuel pump from receiving power. Inspecting the wiring for continuity and checking for voltage drops (should be less than 0.5V) at various points can help identify faults. Repairing or replacing damaged wires is essential to restore proper function. - Visual inspection shows frayed wires, voltage drop measurements indicate poor connectivity, intermittent issues when harness is flexed.
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: Use a professional OBD-II scanner or the GeekOBD APP for a detailed read of fault codes. Focus on P1603 and other related codes to assess the PCM's health and communication status. Ensure to check freeze frame data for additional context regarding when the faults occurred.
- STEP 2 - Battery and Connections Check: Inspect the battery condition using a load tester to ensure it is fully charged and capable of providing adequate voltage (12.4V or higher). Examine all connections to the PCM and fuel pump relay for corrosion or looseness. Ensure that ground connections are secure, as poor grounding can lead to erratic behavior.
- STEP 3 - Relay and Circuit Testing: Test the fuel pump relay for functionality. Measure the resistance across the relay terminals (70-80 ohms is typical) and use a multimeter to confirm that the relay is receiving the correct voltage when energized. If the relay is faulty, replace it with an OEM part (P/N 5016980AA).
- STEP 4 - Wiring Inspection: Conduct a thorough inspection of the wiring harness connected to the PCM, fuel pump, and transmission control module. Look for signs of wear, corrosion, or damage. Perform continuity tests to ensure there are no breaks in the circuit. If issues are found, repair or replace the affected wiring.
