Description

DATA TROUBLE CODE: 78

SYSTEM: Fuel Pump Control Circuit

WIRING DIAGRAM





CIRCUIT DESCRIPTION
The fuel pump speed is controlled at 2 steps (high speed, low speed) by the condition of the engine (starting, light load, heavy load).

When the engine starts (STA ON), the engine control module (ECM) outputs a "High" signal to the fuel pump electronic control unit (ECU) "FPC" terminal. The fuel pump ECU then outputs battery voltage to the fuel pump so that the fuel pump operates at high speed.

After the engine starts, during idling or light loads, the ECM outputs a Low signal to the fuel pump ECU, the fuel pump ECU outputs low battery voltage (about 9 volts) to the fuel pump and causes the fuel pump to operate at low speed.

If the intake air volume increases (high engine load), the ECM sends a "High" signal to the fuel pump ECU and causes the fuel pump to operate at high speed.

DIAGNOSTIC TROUBLE CODE DETECTING CONDITION
- Open or short in fuel pump circuit for 1 second or more with engine speed 1,000 rpm or less. (2 trip detection logic)
OR
- Open in input circuit of fuel pump ECU (FPC) with engine speed 1,000 rpm or less. (2 trip detection logic)
OR
- Open or short in diagnostic signal line (DI) of fuel pump ECU with engine speed 1,000 rpm or less. (2 trip detection logic)

TROUBLE AREA
- Open or short in fuel pump ECU circuit.
- Fuel pump ECU.
- ECM power source circuit.
- Fuel pump.
- ECM.