Code P1221, Fuel Pump Secondary System Circuit Low "S" & "T" Series 4.3L (VIN W): Notes

Status of fuel pump circuit is monitored by control module and is used to compensate fuel delivery based on system voltage. Signal is also used to store a code if fuel pump relay is defective or fuel pump voltage is lost while engine is running. There should be about 12 volts on fuel pump signal circuit for at least 2 seconds after ignition is turned on, or when reference pulses are being received by control module.

1. Checks to see if code was set as the result of a hard or intermittent condition.
2. Checks fuel pump relay.
3. Checks relay power and ground supply circuit.
4. Checks fuel pump relay control circuit connections at relay and control module.
5. Checks oil pressure switch and connections.