Symptoms

- Engine Light ON (or Service Engine Soon Warning Light)

Possible Causes

- Sensor using 5 volt reference line shorted to ground - Circuit short to ground

When Detected

If the voltage is out of tolerance, the PCM will set DTC P1639.

Description

The powertrain control module (PCM) uses the 5-volt reference 2 circuit as a sensor feed for the A/C refrigerant pressure sensor. The PCM monitors the voltage on the 5-volt reference 2 circuit.