I have a faulty BCM on my '05 Trailblazer LT, (rear wipers don't function & seat adjustment memory). Can I fit a replacement BCM from a scrapped vehicle without having to 'flash'.
How do you know the BCM is at fault ? Did you hook up a factory or someother type professional scan tool an check for DTC'S - diagnostic trouble codes ? Did you view how these system work in factory sevice repair information ? Did you use a wiring diagram an DVOM - digital volt ohmmeter an test electrical circuits ?
The BCM has nothing to do with the memory seats .
Memory Seat System Components
The memory seat system consists of the following components:
• Power Seat Switch
• Seat Horizontal Motor
• Seat Front Vertical Motor
• Seat Rear Vertical Motor
• Seat Recliner Motor
• Driver Seat Module
• Memory Seat Switch
Memory Seat System Description
Battery voltage is supplied to the driver seat module through the power seat circuit breaker. The driver seat module supplies the seat adjuster switch assembly with a battery positive reference voltage. While the seat adjuster switches are in an inactive state the switch contacts are closed to the adjuster switch ground circuit. When a seat adjuster switch is pressed to an active state the switch contact is closed to the reference voltage circuit. Battery voltage on a switch signal circuit indicates to the driver seat module the switch status is active. Each seat adjuster motor is controlled by the driver seat module through 2 motor control circuits. While the seat adjuster motors are in an inactive state the motor control circuits are closed to ground circuit contacts within the driver seat module. The driver seat module operates the seat adjuster motors by switching one of a motor's control circuits to battery voltage. The seat adjuster motors are bidirectional and the direction of adjuster motor rotation is determined by which of the adjuster motor control circuits is switched to battery voltage while the other remains grounded.
Memory Set/Recall Operation
The driver seat adjuster motors are equipped with potentiometer type position sensors used by the driver seat module to determine the seat position. The position sensors are supplied with 5-volt reference and ground circuits from the driver seat module. The position sensor signal circuits are referenced from ground within the driver seat module. The signal circuit voltage levels monitored by the driver seat module range from 0.39 - 4.58 volts and are determined by the wiper locations on the resistors within the motor position sensors. The position sensor circuit voltage levels are used by the driver seat module to determine the seat position when storing or recalling memory position settings.
The memory recall switch assembly on the driver's door provides inputs to the driver door module. Battery voltage is supplied to the memory recall switch assembly from the driver door module. When a memory recall 1, 2, or EXIT switch is pressed, the switch contacts close the appropriate switch signal circuit to the battery voltage supply circuit within the memory recall switch assembly. When the driver door module receives active switch signals from the memory recall switch assembly, the appropriate commands are sent to the driver seat module using the Class 2 Serial Data circuit.
Memory seat recall operation is allowed only with the transmission selector lever in the PARK position while the ignition is on. The transmission selector lever position data is provided to the driver seat module by a message through the Class 2 Serial Data circuit.
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Rear Wiper/Washer System Components
The rear wiper/washer system consists of the following components:
• Rear window wiper motor
• Rear washer pump
• Rear wash relay
• Rear wiper/washer switch
• RR WIPER Circuit Breaker 15A / ENDGLASS REG Circuit Breaker 30A
• WASH 20A fuse
• Body control module (BCM)
• Liftgate control module (LGM) / End gate module (EGM)
Rear Wiper Operation (with LGM)
The rear window wiper/washer switch is an input to the BCM. The requested rear wiper mode is sent to the LGM by the BCM, as a message on the serial data circuit. The rear window wiper motor is controlled by the LGM. The switch power circuit to the rear wiper/washer switch is a 12-volt reference supplied by the BCM during ignition on, accessory or RAP power modes. The rear wiper/washer switch is composed from a series of resistors and the switch position is determined by the voltage of the rear wiper/washer switch signal circuit to the BCM. The rear wiper/washer switch has continuity at all times and the BCM expects a rear wiper/washer switch signal voltage in all switch positions including OFF. The rear wiper motor is supplied battery positive voltage and ground. The LGM controls rear wiper motor operation through the rear window motor speed signal circuit. The rear window motor speed signal circuit is supplied a battery positive reference voltage by the rear window wiper motor module and is pulse width modulated to ground by the LGM. The duty cycle of the pulse width modulation determines the rear wiper motor operating mode. The liftglass and liftgate ajar switches are inputs to the LGM and must be in an inactive state in order for rear wiper washer system operation to be enabled. When an ajar switch is active the LGM suspends wiper motor operation directly and sends the ajar switch status messages over the serial data circuit enabling the BCM to suspend washer pump operation.
Rear Wiper Operation (with EGM)
The rear window wiper/washer switch is an input to the BCM. The requested rear wiper mode is sent to the EGM by the BCM, as a message on the serial data circuit. The rear window wiper motor is controlled by the EGM. The switch power circuit to the rear wiper/washer switch is a 12-volt reference supplied by the BCM. The rear wiper/washer switch is composed from a series of resistors and the switch position is determined by the voltage of the rear wiper/washer switch signal circuit to the BCM. The rear wiper/washer switch has continuity at all times and the BCM expects a rear wiper/washer switch signal voltage in all switch positions including OFF. The rear wiper motor is supplied battery positive voltage and ground. The EGM controls rear wiper motor operation through the rear window motor speed signal circuit. The rear window motor speed signal circuit is supplied a battery positive reference voltage by the rear window wiper motor module and is pulse width modulated to ground by the EGM. The duty cycle of the pulse width modulation determines the rear wiper motor operating mode. The rear window motor park signal circuit provides position status of the rear wiper to the EGM.
The rear wiper and washer operation is allowed if the following conditions are true:
• Power mode is run or accessory.
• Lower left ajar switch is closed.
• Upper left ajar switch is closed.
• Upper right ajar switch is closed.
• Upper left dome switch is closed.
• The end gate window is fully closed.
• No end gate window express down, up, or down is requested.
• No gate swing open or drop open is requested.
If rear wiper/washer operation is attempted and the end gate window is open the driver information center (DIC) displays "Tailgate Glass Down". If the rear wiper is not in the park position and an attempt to open end gate window is done, the DIC displays "Rear Wiper Obstruction".
Your best bet , take it to a qualified repair shop because you have no idea how these systems work .
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