DTC P1639: 5-Volt Reference B Circuit: Description

The Powertrain Control Module (PCM) provides a 5-volt reference to the following sensors:

• The Throttle Position (TP) sensor 2.
• The Accelerator Pedal Position (APP) sensor 1.
• The manifold absolute pressure (MAP) sensor.

The PCM monitors voltage on the 5-volt reference circuit. If the voltage is higher or lower than required, DTC P1639 will set.