GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Uplander - 4WD 🢒 Brakes 🢒 Park Brake 🢒 DTC B1370

Circuit Description

The body control module (BCM), monitors the ignition inputs OFF, ignition 3, crank and ignition 1 supplied from the ignition switch. The BCM uses the sequence that the signals appear and their voltage levels to determine the power mode called for by the vehicle operator using the ignition switch. A 12-volt reference voltage is supplied by the BCM to the ignition switch over a discrete circuit. The ignition switch uses this voltage for power mode signal discrimination. When the operator places the ignition switch in the Run or Start position, the ignition 1 circuit is delivers the signal to the BCM.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1370 Device Ignition 1 (ON and START) Circuit

Conditions for Running the DTC
    • The BCM must be powered and must detect a change in the ignition switch circuit states.
    • The vehicle battery must be fully charged.

Conditions for Setting the DTC

The BCM detects that the ignition 1 signal is shorted to ground, voltage or open for more than 10 seconds in the current ignition cycle.

Action Taken When the DTC Sets
    • The BCM stores DTC to memory.
    • The BCM operates in a fail-safe power mode dependent on the last valid power mode detected and the state of the engine run flag data on the class 2 serial data communications circuits.
    • The other modules on the vehicle operate in a fail safe power mode dependent on the last valid power mode transmitted by the BCM and the state of the engine run flag on the class 2 serial data communications circuits.

Conditions for Clearing the DTC
    • A current DTC clears on the next malfunction-free cycle.
    • A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids

A history DTC maybe caused by an intermittent short or open in the ignition 1 circuit. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

  1. This step tests the ignition switch for a short circuit between the 12-volt reference supply circuit and the ignition 1 circuit in the OFF position.

    2.

  2. This step tests the wiring of the ignition 1 circuit for a short to ground or voltage.

  3. This step tests the ignition switch for a closed circuit between the ignition switch 12-volt reference supply circuit and the ignition 1 circuit in the Run and Crank switch positions. Care must be taken as the engine may crank during this test.

Step

Action

Yes

No

Schematic Reference: Body Control System Schematics and Power Distribution Schematics in Wiring Systems

Connector End View Reference: Computer/Integrating Systems Connector End Views and Master Electrical Component List in Wiring Systems

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. Check for DTCs in the range of DTC B1370-B1385 in the body control module (BCM).

Does the scan tool display DTC B1370 to DTC B1385 as current?

Go to Step 3

Go to Diagnostic Aids

3

  1. Disconnect the BCM harness connector that contains the ignition 1 circuit.
  2. Place the ignition switch in the OFF position, leaving the key in the ignition.
  3. Test for a short to ground and a short to voltage between the ignition 1 circuit and the ignition switch 12-volt reference supply circuit at the BCM harness connector. Refer to Body Control System Schematics and Circuit Testing in Wiring Systems.

Did you find a short between the 2 circuits?

Go to Step 4

Go to Step 5

4

  1. Disconnect the ignition switch harness connector.
  2. Test the ignition 1 ignition switch circuit and the ignition switch 12-volt reference supply circuit for a short to ground or voltage at the BCM harness connector. Refer to the following:
    3. •  Circuit Testing in Wiring Systems
    •  Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 9

Go to Step 7

5

Important: The engine may crank during this procedure.

  1. Turn the ignition switch to the RUN position.
  2. Test for continuity between the ignition 1 terminal and the ignition switch 12-volt reference supply terminal on the BCM harness connector. Refer to Circuit Testing in Wiring Systems.
  3. Turn the ignition switch to CRANK.
  4. Test for continuity between the ignition 1 terminal and the ignition switch 12-volt reference supply terminal on the BCM harness connector.

Can you measure continuity in both Run and Crank?

Go to Step 8

Go to Step 6

6

Test the ignition 1 and the ignition switch 12-volt reference supply terminals of the ignition switch harness connector, for intermittent or poor connections, and an open condition.

Did you find and correct the condition?

Go to Step 9

Go to Step 7

7

Replace the ignition switch. Refer to Ignition and Start Switch Replacement in Steering Wheel and Column.

Did you complete the replacement?

Go to Step 9

--

8

Replace the BCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 9

--

9
  1. Reconnect all disconnected connectors.
  2. Install the scan tool.
  3. Turn ON the ignition, with the engine OFF.
  4. Use the scan tool in order to clear the DTCs.
  5. Operate the vehicle within the Conditions for Running the DTCs, as specified in the supporting text.

Does the DTC reset?

Go to Step 1

System OK