DTC P1635: 5-Volt Reference A Circuit: Description

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

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

The Throttle Position (TP) sensor 1.
The Accelerator Pedal Position (APP) sensor 2.
The AC pressure sensor.
The Fuel Tank Pressure (FTP) sensor.
The Oil Pressure Sensor (OPS).

The PCM monitors voltage on the 5-volt reference circuit. If the voltage is higher or lower than required, DTC P1635 will set.