Wiring

1. Disconnect the harness plug from the pressure gradient switch.
2. With the engine coolant temp below 10°C (50°F), test the voltage between the terminals of the plug.
3. With the ignition ON, and the engine not running, battery voltage should be available.
4. With the pressure gradient switch harness plug still disconnected, disconnect the harness plug from the frequency valve.
5. The voltage at the pressure gradient switch harness plug should drop to approx. 4vdc.
6. If voltage values are not within specification, repair wiring as necessary.