The PGM-FI Main Relay is actually comprised of two individual internal relays. When the ignition switch is initially turned ON , the Powertrain Control Module (PCM) supplies ground to the PGM-FI Main Relay. This ground triggers one of the PGM-FI internal relays that sends battery voltage to the fuel pump for two seconds to pressurize the fuel system.
When the engine is running the PCM supplies a continuous ground to the PGM-FI Main Relay. The supplied ground keeps the relay in the "closed" position providing electrical current to the fuel pump, keeping the fuel loop pressurized while the engine runs.
See Figure 1
If the engine is not running with the ignition on, the PCM cuts the ground to the PGM-FI Main Relay, causing the relay to "open" and stop the electric current flow to the fuel pump. As mentioned previously, if the engine is not running, the PCM will only supply ground to the PGM-FI Main Relay for two seconds when the ignition switch is initially switched to the ON position.
The PGM-FI Main Relay also supplies electrical power to the Idle Air Control (IAC) Valve and to the fuel injectors.
If the engine starts and continues to run, the PGM-FI Main Relay is working and does not need to be replaced.
The PGM-FI Main Relay is located as follows:
- Locate and remove the relay.
- Apply battery voltage to the number three terminal.
- Ground the No. 2 terminal.
See Figure 2
- Check for continuity between terminals five and two.
- If continuity is detected, proceed to the step 7.
- If there is no continuity, replace the relay.
- Connect the No. 4 terminal to the positive side of the battery.
- Ground the No. 2 terminal of the relay.
- Check for continuity between the No. 5 terminal and the No. 2 terminal of the relay.
- If there is continuity, the relay checks out OK. If the fuel pump still does not function, check the wiring harness and electrical connectors.
- If there is no continuity, replace the relay and retest.