P1639 CADILLAC – PCM 5 Volt Reference Voltage Circuit Condition

P1639 CADILLAC Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P1639 CADILLAC Possible Causes

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

P1639 CADILLAC 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.