Cutlass V6-191 3.1L VIN M SFI (1998)
Body Function Controller: Description and Operation
A/C Compressor Control
The Powertrain Control Module (PCM) and Body Function Controller (BFC) share hardware and software for control of the AC Compressor Clutch.
The Powertrain Control Module (PCM) and the Body Function Controller (BFC) communicate this information over the serial data Class 2 line.
The Body Function Controller (BFC) performs the following software functions:
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Limit Low Speed Compressor Operation
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Prevent Clutch Slippage
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High Coolant Temperature
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Monitor for Overpressure
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Determine Low Ambient Pressure
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Control Compressor Clutch
The Powertrain Control Module (PCM) performs the following functions:
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Prevent Compressor Overspeed
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Limit Compressor Speed (in PARK or NEUTRAL)
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Drive Compressor Clutch
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Perform Anti-Slug (Slugging is when a mass of liquid enters the AC Compressor Pump)
ABS Indicator
The ABS indicator (amber) will be illuminated when the Electronic Brake Control Module (EBCM) transmits a Class 2 message to the Body Function
Controller (BFC) indicating there is an ABS malfunction. The Body Function Controller (BFC) will then command the ABS indicator ON over the
Serial Peripheral Interface (SPI) data line to the Instrument Cluster. In the event of a Class 2 serial data loss the ABS indicator will illuminate. In the
event of an Serial Peripheral Interface (SPI) data link failure, the ABS indicator will illuminate.
Battery Rundown Function
The Battery Rundown Function helps to prevent the Battery from deep discharge due to interior/courtesy lighting being inadvertently left ON. It
performs this function by turning OFF the inadvertent power output (which provides power for the interior/courtesy lighting).
When the Ignition Switch is turned to the OFF position a time out period is started. This time out period is 3 minutes when the odometer is less than 24
km (15 miles) and it is 20 minutes when the odometer is greater than 24 km (15 miles). When the time out expires the inadvertent power output is
turned off.
Data Line Communications
The Body Function Controller (BFC) communicates on two separate data lines, Class 2 and Serial Peripheral Interface (SPI).
Class 2 Data Line
Class 2 data is a higher speed data transmission. To control serial data line traffic, Class 2 uses the peer to peer method along with message arbitration to
manage data line traffic. The control modules on the Class 2 data line are:
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Body Function Controller (BFC)
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Electronic Brake Control Module (EBCM)
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Powertrain Control Module (PCM)
Serial Peripheral Lnterface (Spi) Data Line
The Serial Peripheral Interface (SPI) is a three wire interface connecting the Body Function Controller (BFC) to the Instrument. Cluster, which allows
for them to exchange information. This interface is a synchronous serial data link where the Body Function Controller (BFC) is the master and the
Instrument Cluster is the slave. Because of the need for modules on the different serial data links to communicate with each other, the Body Function
Controller (BFC) acts as an interpreter, or master, for data communication between the Class 2 and Serial Peripheral Interface (SPI) data lines.
Brake Indicator
The BRAKE warning indicator (red) will be illuminated when the Ignition Switch is in RUN position and the Park Brake is engaged. The BRAKE
indicator will illuminate when the Electronic Brake Control Module (EBCM) transmits a Class 2 message to the Body Function Controller (BFC)
indicating there has been a Brake Fail Condition. The Body Function Controller (BFC) will then command the BRAKE indicator ON over the Serial
Peripheral Interface (SPI) data line to the Instrument Cluster. In the event of the Electronic Brake Control Module (EBCM) commanding the BRAKE
indicator to illuminate the Cruise function will be canceled. In the event of a Class 2 serial data loss the BRAKE indicator will illuminate. In the event of
an Serial Peripheral Interface (SPI) data link failure, the BRAKE indicator will not illuminate unless the indicator was illuminated prior to the Serial
Peripheral Interface (SPI) data link failure.
Bulb Check General Description
The bulb check function resides in the Body Function Controller (BFC). Every time the Ignition Switch transitions from ACC to RUN, an Instrument
Cluster bulb check will occur for a calibrated amount of time for specified indicators. Bulb check will override the OFF state of the affected indicators.
