Description
DATA TROUBLE CODE: 78SYSTEM: Fuel Pump Control Circuit
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 sends a High signal to the Fuel Pump Electronic Control Unit (FPC terminal).
The Fuel Pump Electronic Control Unit then outputs High voltage (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 Engine Control Module outputs a High Low signal to the Fuel Pump Electronic Control Unit, the Fuel Pump Electronic Control Unit 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 Engine Control Module sends a High signal to the Fuel Pump Electronic Control Unit 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 Electronic Control Unit with engine speed 1,000 rpm or less (2 trip detection logic).
OR
- Open or short in diagnostic signal line (D1) of Fuel Pump Electronic Control Unit with engine speed 1,000 rpm or less (2 trip detection logic).
TROUBLE AREA
- Open or short in Fuel Pump Electronic Control Unit circuit.
- Fuel Pump Electronic Control Unit.
- Engine Control Module power source circuit.
- Fuel Pump.
- Engine Control Module.
Malfunction Indicator Lamp
Normal Mode On
Test Mode On