P1639 SATURN PCM 5 Volt Reference Voltage Circuit Condition

Possible causes
– Sensor using 5 volt reference line shorted to ground
– Circuit short to ground
When is the code detected?
If the voltage is out of tolerance, the PCM will set DTC P1639.
Symptoms
– Engine Light ON (or Service Engine Soon Warning Light)
P1639 SATURN 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.