For 1990-2009 cars

### Circuit Description

The body control module (BCM) monitors the ignition 1 signal from the ignition switch. When the vehicle operator places the ignition switch in the RUN or CRANK position, the switch supplies B+ to the BCM ignition 1 input terminal. If this circuit becomes shorted to B+, ground or the circuit opens, DTC B1370 will set.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B1370 Device Ignition 1 Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .

DTC Symptom | DTC Symptom Descriptor
--- | ---
01 | Short to Battery
02 | Short to Ground

### Conditions for Running the DTC

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

### Conditions for Setting the DTC

• | The BCM detects a short to ground in the ignition 1 voltage circuit when the ignition switch is in RUN or CRANK.

• | The BCM detects a short to battery or an open in the ignition 1 voltage circuit when the switch is in the OFF position.

• | Any of the conditions above must be present for more than 10 seconds.

### 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 GMLAN 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 GMLAN serial data communications circuits.

### Conditions for Clearing the DTC

• | A current DTC clears when the malfunction is no longer present.

• | 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 may be caused by an intermittent short or open in the ignition 1 circuit. Refer to Testing for Intermittent Conditions and Poor Connections .

### Test Description

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

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

3. This 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 | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Body Control System Schematics and Power Distribution Schematics Connector End View Reference: Master Electrical Component List
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. Check for DTCs B1370 and B1380 in the body control module (BCM).

Does the scan tool display DTC B1370 or DTC B1380 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 Circuit Testing .

Did you find a short between the 2 circuits?

B+

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 Circuit Testing .

Did you find and correct the condition?

B+

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 .
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 . 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