Low Pressure Shutoff Relay Circuit -- CNG Engine Only

Name of Code:
Low Pressure Shutoff Relay Control Circuit.

When Monitored:
With ignition key ON and battery voltage greater than 10 volts.

Theory of Operation:
Low Pressure Shutoff Relay controls the 12-volt source to the fuel injectors. Ignition coil(s), oxygen sensor(s), and the generator. (And low pressure shutoff solenoid on CNG). The relay is located in the Power Distribution Center (PDC). One side of the relay control coil is supplied with battery voltage when the ignition switch is in the start or run position. The circuit is completed when the other side of the relay coil is grounded by the Powertrain Control Module (PCM). The PCM grounds the control circuit when the ignition switch is in the start or run position and engine RPM is detected. If engine RPM is not detected, the PCM will remove the Low Pressure Shutoff relay control circuit ground.

Possible Causes:
- Relay coil open or shorted.
- Fused ignition switch output circuit open.
- Low Pressure Shutoff relay control circuit open or shorted
- Inoperative circuit driver in PCM (PCM Failure) Connector terminals

NOTE: The auto shutdown relay is referred to as the Low Pressure Shutoff Relay in CNG applications.