| CAUTION | If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. |
Circuit Description
Fuel pump is controlled in one of 3 speeds by fuel pump Electronic Control Unit (ECU) depending upon engine load and engine speed. Fuel pump ECU is controlled by ECM. Under high engine load and high engine speed, ECM applies about 3.8 volts to fuel pump ECU. Fuel pump ECU then applies battery voltage to fuel pump, resulting in high speed fuel pump operation. Under medium engine load and low engine speed, ECM applies about 2.5 volts to fuel pump ECU. Fuel pump ECU then applies about 10 volts to fuel pump, resulting in medium speed fuel pump operation. With engine idling or under light load, ECM applies about 1.3 volts to fuel pump ECU. Fuel pump ECU then applies about 8.5 volts to fuel pump, resulting in low speed fuel pump operation. DTC is set when ECM detects an open or short in a fuel pump ECU circuit with engine speed of 1000 RPM or less. Possible causes are
- Fuel pump ECU circuit is open or shorted.
- Defective fuel pump ECU.
- Defective ECM power source circuit.
- Defective fuel pump.
- Defective ECM.
Diagnostic Aids
Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.