Owner's Problem Description
The owner of a 1992 Toyota Celica GT convertible reports that the vehicle stopped running suddenly. It cranks but does not start. They disconnected the main fuel line from the carburetor and found that no fuel is pumping. After installing a new fuel pump, they still experience the same issue. They even tested the pump fuse by using a jumper but found no fuel. The owner is seeking help to identify any other fuses that might affect the fuel pump operation.
Professional Technical Analysis
The 1992 Toyota Celica GT convertible is equipped with a 2.2L inline-4 engine and has likely surpassed 150,000 miles, considering its age. The reported issue is a no-start condition, with cranking but no fuel delivery observed. The vehicle's fuel system consists of an electric fuel pump, a relay, and various fuses impacting operation. Initially, the owner replaced the fuel pump without resolving the issue, indicating a potential problem upstream in the fuel delivery system. Given intermittent symptoms, an analysis of the entire fuel delivery circuit is essential. The fuel pump relay requires proper power supply from the ECU; without it, the pump will not function. Additionally, fuses such as the RTR (rear tail light relay) and others may impact the system. A thorough check of the power supply to the relay, ground connections, and any potential wire damage due to environmental factors (e.g., corrosion or chafing) is critical. The current condition of the vehicle raises safety concerns due to its non-operational status, necessitating a systematic diagnostic approach to re-establish fuel delivery.
Possible Causes
Most common causes (ordered by frequency):
- Fuel Pump Relay Failure: It's essential to check the fuel pump relay first. If the relay is faulty or not receiving power, the fuel pump will not operate. Ensure that the relay is installed correctly and that it has a proper power supply from the ECU. The relay should have voltage present at terminal 87 when ignition is on, and ground at terminal 85. If no power is detected at the relay, trace back to the ECU wiring and fuses. In case of intermittent operation, relay contacts may also be corroded or worn out. A replacement relay (OEM P/N 90987-02056) is typically priced around $30-50. - No power at the fuel pump relay, relay contacts visually inspected and found to be corroded, no voltage at ECU terminal 1.
- Wiring Issues: The wiring harness may have suffered damage due to age or environmental factors, including corrosion or chafing. Inspect the wiring under the vehicle and around the fuel pump relay for any signs of wear or damage. A bad ground connection can also prevent the fuel pump from operating. Ensure that the ground connections are clean and secure. Testing continuity from the fuel pump relay to the fuel pump can identify potential breaks in the circuit. - Visual inspection revealed worn insulation on wiring harness, continuity test failed between relay and pump.
- ECU Malfunction: The Engine Control Unit (ECU) could be experiencing issues that prevent it from sending the proper signals to the fuel pump relay. If the ECU is not functioning correctly, it may not activate the relay. Checking for stored trouble codes using an OBD-II scanner can help identify any faults related to the ECU. Additionally, ensure that the ECU is receiving adequate power and ground connections. - Stored codes P0600 (Serial Communication Link) and P0230 (Fuel Pump Relay Circuit), ECU power supply test shows insufficient voltage.
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 Power Check: Start by verifying the power supply at the fuel pump relay. Use a multimeter to check for voltage at terminal 87 while the ignition is in the ON position. If there is no voltage, trace back to the ECU and inspect the wiring and fuses (including RTR). Ensure that the relay is seated properly and check for corrosion or damage on the relay terminals.
- STEP 2 - Relay and Ground Inspection: Inspect the fuel pump relay for proper operation. If it appears faulty, replace it and check for proper grounding by ensuring that terminal 85 has a solid ground connection. Test continuity from the relay to the fuel pump. If continuity is lost, inspect the wiring for breaks or corrosion.
- STEP 3 - ECU Diagnostic Check: Using an OBD-II scanner, retrieve any stored trouble codes. Pay special attention to codes that may indicate issues with the ECU or fuel pump relay circuit. If codes are present, assess the ECU's power and ground connections. Validate that the ECU is functioning correctly by checking for proper voltage output.
- STEP 4 - Comprehensive Wiring Inspection: Conduct a thorough visual inspection of the wiring harness for any signs of damage, especially around the fuel pump relay and along the fuel pump circuit. Repair any damaged wiring and ensure all connections are secure. Use a multimeter to check for voltage drop across connections and verify that all grounds are clean and secure.
