Circuit Description

The powertrain control module (PCM) provides 5 volts to the following sensors.

• The manifold absolute pressure (MAP) sensor (Pontiac)
• The air conditioning (A/C) refrigerant pressure sensor (Buick)
• The exhaust gas recirculation (EGR) valve
• The fuel tank pressure (FTP) sensor
• The secondary AIR pressure sensor (L26, NU3 only)

A circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects that the voltage is out of tolerance, DTC P0641 sets.