DTC P1635: 5-Volt Reference Circuit "A" Or No. 1: Description

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Powertrain Control Module (PCM) provides 5-volts to the following sensors:

Manifold Absolute Pressure (MAP) sensor.
Exhaust Gas Recirculation (EGR) valve pintle position sensor.
Fuel Tank Pressure (FTP) sensor (except Bonneville and Regal).
Throttle Position (TP) sensor.

These 5 volt reference circuits are independent of each other outside the PCM, but are bussed together inside the PCM. Therefore a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt circuits. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects that the voltage is out of tolerance, DTC P1635 sets.