P1639 FIAT PCM 5 Volt Reference Voltage Circuit Condition

Possible causes

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

What about the obd code?

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

Symptoms

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

P1639 FIAT 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.