Circuit/System Description

The engine control module (ECM) has 3 internal 5-volt reference busses called 5-volt reference 1, 5-volt reference 2, and 5-volt reference 3. Each reference bus provides 5-volt reference circuits for more than one sensor. Therefore, a fault condition on one 5-volt reference circuit will affect the other 5-volt reference circuits connected to that reference bus. The ECM monitors the voltage on the 5-volt reference busses.

The 5-volt reference 1 bus provides 5 volts to the following sensors:

• The manifold absolute pressure (MAP) sensor
• The clutch apply sensor
• The fuel rail sensor
• The fuel tank pressure (FTP) sensor
• The intake air pressure and temperature sensor

The 5-volt reference 2 bus provides 5 volts to the following sensors:

• The accelerator pedal position (APP) sensor 1
• The exhaust camshaft position (CMP) sensor
• The intake camshaft position (CMP) sensor

The 5-volt reference 3 bus provides 5 volts to the following sensors:

• The APP sensor 2
• The crankshaft position (CKP) sensor
• The air conditioning (A/C) refrigerant pressure sensor
• The throttle position (TP) sensor 1 and 2
• The brake booster vacuum sensor