DTC P1639: 5-Volt Reference "B" Circuit: Description

Powertrain Control Module (PCM) uses the 5-volt reference "B" circuit as a sensor feed to the A/C pressure sensor and Fuel Tank Pressure (FTP) sensor. The PCM monitors voltage on the 5-volt reference "B" circuit. If the voltage is out of tolerance, Diagnostic Trouble Code (DTC) P1639 will set.