Tag Archives: Voltage Variations
Keep Alive Memory (KAM)
The PCM stores information in KAM (a memory integrated circuit chip) about vehicle operating conditions, and then uses this information to compensate for component variability. KAM remains powered when the vehicle key is off so that this information is not lost.
Keep Alive Power (KAPWR)
The PCM stores the vehicle operating conditions in the KAM and uses this information to compensate for component variability. The KAPWR circuit supplies a constant battery voltage (B+) input to the PCM to maintain the memory contents when the key is in the OFF position.
Power Ground (PWR GND)
The PWR GND circuit(s) is directly connected to the battery negative terminal. PWR GND provides a return path for the PCM VPWR circuits.
Reference Voltage (VREF)
VREF is a consistent positive voltage (5.0 volts ±0.5) provided by the PCM. VREF is typically used by 3-wire sensors and some digital input signals.
Signal Return (SIG RTN)
The SIG RTN circuit(s) is a dedicated return path for VREF applied components.
Vehicle Buffered Power (VBPWR)
VBPWR is a regulated voltage supplied by the PCM to vehicle sensors. These sensors require a constant 12 volts for operation and cannot withstand VPWR voltage variations. VBPWR is regulated to VPWR minus 1.5 volts and is also current limited to protect the sensors.
Vehicle Power (VPWR)
VPWR is the primary source of PCM power. VPWR is switched through the PCM power relay and is controlled by the ignition switch. With the key in the START or RUN position, voltage is supplied to the PCM power relay coil. The supplied voltage energizes the relay and closes the internal relay contacts. With the relay contacts closed, VPWR is supplied to the PCM.