GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Chevy C Silverado - 2WD 🢒 Body and Accessories 🢒 Body Control System 🢒 DTC B1398 Device Voltage Reference Out #1 CKT High

Object Number: 367983 Size: MF
Body Control Module Components
Body Control System Schematics
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The body control module (BCM) provides a constant output reference voltage (5 volts) for the proper operation of the ambient light sensor. The constant output reference voltage supply ensures that variations in the output signal of the ambient light sensor is due to changes of the sensor rather than variations in the voltage supply. The BCM monitors the constant output reference voltage (5 volts) and sets a DTC when the output is not within the expected range (4.75-5.25 volts).

Conditions for Setting the DTC
    • When the ignition switch in the RUN position, the 5 volt reference output CKT 705 is greater than 5.25 volts (shorted to battery).
    • The system voltage must be between 9.0-16.0 volts.
    • The above conditions must be met for 0.5 seconds.

Action Taken When the DTC Sets

The daytime running lamps (DRL) feature will not operate.

Conditions for Clearing the MIL/DTC
    • A DTC will clear immediately after the condition for setting the fault is corrected.
    • A history DTC will clear after 100 consecutive ignition cycles without a fault present.
    • Use a scan tool in order to clear history and current DTCs.

Diagnostic Aids
    • Always diagnose the first DTC listed on the scan tool.
    • The scan tool must display DTC B1398 as a current code before performing diagnostics.
    • Perform a visual inspection for loose or poor connections at all related components.
    • Refer to Intermittents and Poor Connections in Wiring Systems.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. This step determines if the BCM 5 volt reference is defective or if CKT 705 is shorted to battery. By disconnecting the BCM connector, other DTCs will set

Step

Action

Value(s)

Yes

No

1

Was the BCM Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check - Body Control System

2
  1. Turn the ignition switch to the ON position.
  2. With a scan tool, select BCM.
  3. Monitor the current DTCs.
  4. Disconnect the purple BCM (C3) connector.

Does the scan tool display DTC 1398?

--

Go to Step 4

Go to Step 3

3

Locate and repair the short to battery in CKT 705 (GRY) between the purple BCM C3 connector and the ambient light sensor.

Is the repair complete?

--

Go to Step 5

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4
  1. Replace the BCM. Refer to Body Control Module Replacement .
  2. Program BCM with the proper calibrations. Refer to Body Control Module (BCM) Programming/RPO Configuration .
  3. Perform the learn procedure.

Is the repair complete?

--

System OK

--

5

Clear the DTCs. Refer to Clearing DTCs .

Is the repair complete?

--

System OK

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