DTC B1785 Recline Motor CKT Malfunction. GMC Truck Sonoma Pickup

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1999 🢒 Sonoma Pickup - 2WD 🢒 DTC 🢒 DTC B1785 Recline Motor CKT Malfunction

Refer to

Cell 141: Memory Seat Module, Transducers and Motors

Power Seat Connector End Views
Handling ESD Sensitive Parts Notice
Power Seat Systems Components
Memory Seat Circuit Description
Cell 141: Power, Ground, DLC and Power Seat Adjuster Switch
Handling ESD Sensitive Parts Notice
.

Circuit Description

The memory seat module (MSM) controls the seat recliner motor power and ground through CKT 276 (LT GRN) and CKT 277 (LT BLU). The MSM also senses the seat recliner motor position through a hall sensor within the motor through CKT 570 (WHT/BLK) while utilizing CKT 570 (BLK) as a sensor ground.

Conditions for Setting the DTC

The DTC will set if the MSM detects through the hall sensor that the recliner motor is not responding to the MSM commands due to the following conditions:

•	An open circuit

•	A short to ground

•	A short to power

•	An inoperative motor

Conditions for Clearing the DTC

•	A history DTC will clear after 100 consecutive fault free ignition cycles.

•	Use a scan tool in order to clear history and current DTCs.

Diagnostic Aids

One or more of the following conditions may be the cause of an intermittent failure:

•	A poor connection

•	A break in the wire insulation that exposes the internal wire

•	A wire broken inside the insulation

Test Description

The numbers below refer to the step numbers on the diagnostic table.

This step inspects for current DTCs.

This step inspects the wiring between the seat recliner motor and the MSM for open circuits.

This step repairs the open(s) in the wiring between the seat recliner motor and the MSM.

This step inspects the wiring between the seat recliner motor and the MSM for short(s) to ground.

This step repairs the short(s) to ground in the wiring between the seat recliner motor and the MSM.

This step verifies proper MSM operation.

This step replaces a defective seat recliner motor.

This step replaces a defective MSM.

Step

Action

Value(s)

Yes

Did you perform the Power Seat Systems Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Power Seat Systems

Turn the ignition switch to the OFF position.
Install the scan tool.
Turn the ignition switch to the RUN position.
Using the scan tool, clear the DTCs.
Operate the MSM controls.

Does DTC B1785 reset?

Go to Step 3

Go to Diagnostic System Check - Power Seat Systems

Disconnect the MSM and the motor.
Using a J 39200 digital multimeter (DMM), test the continuity of each of the following circuits from the memory seat module (MSM) to the seat recliner motor:

•	CKT 276 (LT GRN)

•	CKT 277 (LT BLU)

•	CKT 570 (BLK)

•	CKT 570 (WHT/BLK)

Is continuity present on all circuits?

Go to Step 5

Go to Step 4

Locate and repair the open circuit(s).

Is the repair complete?

Go to Diagnostic System Check - Power Seat Systems

Disconnect the MSM.
Use a J 39200 DMM in order to test for continuity to ground at each of the following circuits at the MSM connector:

•	CKT 276 (LT GRN)

•	CKT 277 (LT BLU)

•	CKT 570 (BLK)

•	CKT 570 (WHT/BLK)

Is continuity present on any circuit?

Go to Step 6

Go to Step 7

Locate and repair the short(s) to ground.

Is the repair complete?

Go to Diagnostic System Check - Power Seat Systems

Reconnect the MSM connector
Disconnect the seat recliner motor and connect a test lamp between the CKT 276 (LT GRN) and CKT 277 (LT BLU) terminals of the connector.

Does the lamp light when the recliner switch is in the FORWARD and BACK positions?

Go to Step 8

Go to Step 9

Replace the recliner motor.

Is the repair complete?

Go to Diagnostic System Check - Power Seat Systems

Replace the MSM.

Is the repair complete?

Go to Diagnostic System Check - Power Seat Systems