GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 GMC C Sierra - 2WD 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC B1375

Circuit Description

The ignition 3 voltage circuit is a discrete input to the HVAC control module. The HVAC control modules uses the input to determine that the ignition switch is in the RUN position. When the ignition switch is in the RUN position, ignition voltage is applied to the input.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1375 Device Ignition 3 Circuit

Conditions for Running the DTC
    • Source voltage is 8.7-16.5 volts.
    • The HVAC control module receives a RUN power mode message from the body control module (BCM) over the class 2 serial data circuit.

Conditions for Setting the DTC

The HVAC control module does not detect ignition voltage on the ignition 3 voltage input.

Action Taken When the DTC Sets

The HVAC control module will continue to operate using the class 2 power mode messaging.

Conditions for Clearing the DTC
    • The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
    • The history DTC will clear after 100 fault-free ignition cycles.
    • The DTC can be cleared with a scan tool.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Select the HVAC control module display DTC function on the scan tool.

Does the scan tool indicate that B1375 is a current DTC?

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections

3
  1. Turn OFF the ignition.
  2. Disconnect the HVAC control module.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 3 voltage circuit with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 5

4

Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

Go to Step 7

Go to Step 6

5

Repair the ignition 3 voltage circuit. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 7

--

6

Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 7

--

7
  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 3

System OK