GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2005 🢒 Ascender - 4WD 🢒 Accessories 🢒 Navigation Systems 🢒 DTC B1721

Circuit Description

The driver door module (DDM) supplies battery positive voltage to the power mirror switch. When the mirror direction switch is placed in the left or right position, the signal circuit is switched to battery voltage. The driver door module senses the voltage change and activates the selected outside rearview mirror in the appropriate direction.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1721 Mirror Left and Right Control Switch Circuit

Conditions for Running the DTC
    • Battery voltage must be between 9-16 volts.
    • The ignition switch is in the ON position.

Conditions for Setting the DTC

The DDM senses an active state on both the mirror switch left and right signal circuits greater than 3 seconds.

Action Taken When the DTC Sets

The DDM will ignore the continuous inputs from the switch. The DDM will respond to all other valid switch inputs.

Conditions for Clearing the MIL/DTC

When the fault is no longer present, the door module changes the current DTC to a history DTC. The door module will clear the history DTC after 50 fault free ignition cycles, or in response to a scan tool command.

Step

Action

Yes

No

Schematic Reference: Outside Rearview Mirror Schematics

Connector End View Reference: Power Door Systems Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Place the mirror direction switch in the IDLE position.
  4. With a scan tool, observe the Mirror Switch Horizontal data parameter in the door module data list.

Does the scan tool display Idle?

Go to Step 3

Go to Step 4

3
  1. Activate the mirror direction switch to both the left and right positions.
  2. With the scan tool, observe the Mirror Switch Horizontal data parameter.

Does the Mirror Switch Horizontal data parameter change state appropriately with each selection?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 4

4
  1. Disconnect the mirror switch.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the Mirror Switch Horizontal data parameter.

Does the scan tool display Idle?

Go to Step 7

Go to Step 5

5

Inspect for poor connections at the harness connector of the driver door module (DDM). Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 6

6

Replace the DDM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 8

--

7

Replace the mirror switch. Refer to Power Mirror Switch Replacement .

Did you complete the replacement?

Go to Step 8

--

8
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK