B1840 - Driver Lumbar Up Switch CKT Malf (With AM3)

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
The memory seat module (MSM) lumbar vertical switches are normally open. They apply 12 V to the massage module when they are pressed. This input is relayed by the massage module to the MSM, if the massage function is not presently requested. The MSM, in turn, will relay this input back to the massage module and the massage module then commands the seat to move in response of the switch input.

CONDITIONS FOR RUNNING THE DTC
The MSM must be powered and can not have DTC B1327 - Battery Voltage Low as an active DTC for this DTC to set.

CONDITIONS FOR SETTING THE DTC
^ If a seat switch continues to be active for 30 seconds after a motor controlled by that switch reaches the end of its travel, the switch will be considered shorted and the MSM will set the DTC.
^ If a position sensor DTC is current and the associated switch is active for 30 continuous seconds, the switch will be considered shorted and the MSM will set a switch DTC.
^ A switch DTC will not set if DTC B1327 or B1328 is current.

ACTION TAKEN WHEN DTC SETS
^ A motor output driven in response to a switch considered tailed, is deactivated for both directions.
^ All memory recall commands are ignored.
^ The MSM will respond to any other switch input that has not set a DTC.

CONDITIONS FOR CLEARING THE DTC
The DTC automatically clears when the switch circuit setting the DTC is no longer active.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. Checks the existing state of the driver's seat lumbar switch by using the current state of the input parameter. If all of the seat switch parameters display active, possibly one of the seat switch input circuits is shorted to voltage.
4. When the seat switch is disconnected, this step determines if the seat switch contacts are stuck closed, or if one of the switch input circuits is possibly shorted to voltage.
5. Determines if there is a short to battery positive voltage (B+) in the switch input circuit.
7. Determines if there is a short to battery positive voltage (B+) in the lumbar up output circuit of the massage module.
14. This step verifies the repair.

For a description of the RPO Code(s) shown in this image/article refer to the RPO Code List found at Vehicle/Application ID RPO Codes