B3921
DTC B3920 or B3921
DTC Descriptors
This diagnostic procedure supports the following DTCs:
DTC B3920 01
- Group 1 Seat Motors Circuit Shorted to Battery or Open
DTC B3920 02
- Group 1 Seat Motors Circuit Shorted to Ground
DTC B3921 01
- Group 2 Seat Motors Circuit Shorted to Battery or Open
DTC B3921 02
- Group 2 Seat Motors Circuit Shorted to Ground
Diagnostic Fault Information
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
Circuit/System Description
The memory seat module (MSM) controls the seat, recline, lumbar, and steering column motors via half bridges that are divided into 2 groups that are connected to separate power rails internal to the module.
Power rail 1 includes of the following motors:
* Seat front vertical motor
* Seat rear vertical motor
* Seat horizontal motor
* Seat recline motor
* Seat lumbar horizontal motor
Power rail 2 includes the following motors:
* Driver seat lumbar vertical motor
* Passenger seat lumbar vertical motor
* Steering column tilt actuator
* Steering column telescope actuator
The MSM connects all of the motor control circuits on each power rail to a common reference point whenever they are not in operation. This reference point is biased to approximately 2.5 volts. The MSM checks to see if this reference voltage is shorted to ground or battery before enabling any seat, lumbar, or steering column motor.
Diagnostic Aids
The scan tool may reference the Memory Seat Module (MSM) as the Driver Position Module.
Conditions for Running the DTC
B3920
All motor outputs for power rail 1 must be inactive for this DTC to set.
B3921
All motor outputs for power rail 2 must be inactive for this DTC to set.
Conditions for Setting the DTC
B3920 01
The voltage on any power rail 1 motor control circuit exceeds 2.78 volts for 100 ms.
B3920 02
The voltage on any power rail 1 motor control circuit is below 1.47 volts for 100 ms.
B3921 01
The voltage on any power rail 2 motor control circuit exceeds 2.78 volts for 100 ms.
B3921 02
The voltage on any power rail 2 motor control circuit is below 1.47 volts for 100 ms.
Action Taken When the DTC Sets
The MSM will not allow operation of any motor on the power rail for which the DTC was set.
Conditions for Clearing the DTC
* The current DTC clears and sets to history when the reference voltage is between 1.47 volts and 2.5 volts for 3 seconds and the power mode changes to OFF then back to ACC or RUN.
* The history DTC will clear after 50 consecutive fault-free ignition cycles have occurred.
Circuit/System Testing
B3920 Group 1 Motors
1. Ignition OFF, disconnect the (C1) harness connector at the memory seat module.
2. Ignition ON, verify that a test does not illuminate between any of the following motor control circuits and ground:
* Front vertical motor terminal 12
* Front vertical motor terminal 13
* Rear vertical motor terminal 15
* Rear vertical motor terminal 16
* Seat horizontal motor terminal 9
* Seat horizontal motor terminal 10
• If the test lamp illuminates, test the control circuit for a short to voltage.
3. Test for infinite resistance between the following motor control circuits and ground:
* Front vertical motor terminal 12
* Front vertical motor terminal 13
* Rear vertical motor terminal 15
* Rear vertical motor terminal 16
* Seat horizontal motor terminal 9
* Seat horizontal motor terminal 10
• If less than infinite resistance, test the motor control circuit for a short to ground.
4. Test for greater resistance values than specified between the following motor control circuits:
* 1 ohm for front vertical motor terminal 12 and terminal 13
* 1 ohm for rear vertical motor terminal 15 and terminal 16
* 1 ohms for seat horizontal motor terminal 9 and terminal 10
• If less than the specified resistance, test the control circuits for a short together or shorted motor.
5. Ignition OFF, disconnect the (C4) harness connector at the memory seat module.
6. Ignition ON, verify that a test does not illuminate between any of the following motor control circuits and ground:
* Lumbar horizontal motor terminal 12
* Lumbar horizontal motor terminal 13
* Seat recline motor terminal 15
* Seat recline motor terminal 16
• If the test lamp illuminates, test the control circuit for a short to voltage.
7. Test for infinite resistance between the following motor control circuits and ground:
* Lumbar horizontal motor terminal 12
* Lumbar horizontal motor terminal 13
* Seat recline motor terminal 15
* Seat recline motor terminal 16
• If less than infinite resistance, test the motor control circuit for a short to ground.
8. Test for greater resistance values than specified between the following motor control circuits:
* 10 ohms for lumbar horizontal motor terminal 12 and terminal 13
* 1 ohm for recline motor terminal 15 and terminal 16
• If less than the specified resistance, test the control circuits for a short together or shorted motor.
9. If all circuits test normal, replace the memory seat module.
B3921 Group 2 Motors
1. Ignition OFF, disconnect the (C4) harness connector at the memory seat module.
2. Ignition ON, verify that a test lamp does not illuminate between any of the following motor control circuits and ground:
* Driver seat lumbar vertical motor terminal 1
* Driver seat lumbar vertical motor terminal 2
* Passenger seat lumbar vertical motor terminal 4
* Passenger seat lumbar vertical motor terminal 5
* Steering column tilt actuator terminal 7
* Steering column tilt actuator terminal 8
• If the test lamp illuminates, test the control circuit for a short to voltage.
3. Test for infinite ohms of resistance between the following motor control circuits and ground:
* Driver seat lumbar vertical motor terminal 1
* Driver seat lumbar vertical motor terminal 2
* Passenger seat lumbar vertical motor terminal 4
* Passenger seat lumbar vertical motor terminal 5
* Steering column tilt actuator terminal 7
* Steering column tilt actuator terminal 8
• If less than infinite, test the control circuit for a short to ground.
4. Test for greater resistance values than specified between the following motor control circuits:
* 10 ohms for driver seat lumbar vertical motor terminal 1 and terminal 2
* 10 ohm for passenger seat lumbar vertical motor terminal 4 and terminal 5
* 1 ohm for steering column tilt actuator terminal 7 and terminal 8
• If less than the specified resistance, test the control circuits for a short together or shorted motor.
5. Ignition OFF, disconnect the (C1) harness connector at the memory seat module.
6. Ignition ON, verify that a test lamp does not illuminate between any of the following actuator control circuits and ground:
* Steering column telescope actuator terminal 8
* Steering column telescope actuator terminal 7
• If the test lamp illuminates, test the control circuit for a short to voltage.
7. Test for infinite ohms of resistance between the following actuator control circuits and ground:
* Steering column telescope actuator terminal 8
* Steering column telescope actuator terminal 7
• If less than infinite, test the control circuit for a short to ground.
8. Test for greater than 1 ohm of resistance between the steering column telescope actuator control circuits terminal 7 and terminal 8.
• If less than 1 ohm, test the control circuits for a short together or shorted actuator.
9. If all circuits test normal, replace the memory seat module.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Front Seat Adjuster Replacement
* Power Recliner Motor Replacement - Front Seat
* Lumbar Replacement - Front Seat (w/AL2) Lumbar Replacement - Front Seat (w/AM3)
* Tilt Actuator Assembly Replacement
* Telescope Actuator Switch Replacement
* Programming and Relearning for MSM programming and setup. Programming and Relearning