For 1990-2009 cars

### Circuit Description

When the ignition is switched on, the antenna that is integrated in the theft deterrent control module (Immobilizer) is energized. During this period the engine control module (ECM) sends a signal to the intelligent switching unit (ISU) requesting the frequency code.

The transponder key contains a security code (transponder code) that transmits via the antenna to the theft deterrent control module. The theft deterrent control module sends the code to the ISU. The ISU compares the received code with the stored transponder code. If the transponder code is recognized, the ISU blocks the speed signal input to the ECM allowing the transfer of the frequency code to the ECM. The ECM compares the received frequency code with the programmed frequency code. If the signal is recognized and matches the programmed signal the engine is allowed to start.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC 037 Immobilizer Antenna Short to Ground or Open

### Conditions for Running the DTC

Vehicle battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

• | Short to ground on the theft deterrent .

• | Open circuit on the theft deterrent

• | Open circuit on the theft deterrent

### Action Taken When the DTC Sets

• | The security lamp is on solid with ignition ON.

• | The vehicle will not start.

### Conditions for Clearing the DTC

• | A history DTC will clear after 40 consecutive ignition cycles if the condition for the malfunction is no longer present.

• | Use a scan tool in order to clear DTCs.

Step | Action | Yes | No
--- | --- | --- | ---
Important: You must obtain all the keys from the vehicle owner before testing. If a component needs to be replaced, any vehicle keys not programmed during the programming procedure will be inoperative after the programming sequence is completed. Ensure that the doors, hood and trunk/rear hatch are closed prior to starting the programming procedure. If the system is placed in program mode, then the ISU will erase all previously programmed transmitters upon the receipt of the first transmitter s programming signal. Do not operate or program the transmitters in the vicinity of other vehicles that are also in the keyless entry program mode. This prevents the programming of the transmitters to the incorrect vehicle.

Schematic Reference: Theft Deterrent System Schematics

Connector End View Reference: Theft Deterrent System Connector End Views

1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Disconnect the theft deterrent control module.
2. Test the communication signal circuit at the theft deterrent control module for short to ground. Refer to Circuit Testing and Wiring Repairs .

Was voltage present?

Go to Step 3

Go to Step 4

3 |

1. Disconnect the intelligent switching unit (ISU).
2. Test the communication signal circuit at the theft deterrent control module for short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 7

Go to Step 6

4 |

1. Disconnect the ISU.
2. Test both communication signal circuits at the theft deterrent control module for an open circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

Go to Step 7

Go to Step 5

5 | Inspect for poor connections at the harness connector of the ISU. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 9 | Go to Step 8
6 | Inspect for poor connections at the harness connector of the theft deterrent control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 9 | Go to Step 7
7 | Important: Perform the program procedure for the theft deterrent control module. Replace the theft deterrent control module. Refer to Theft Deterrent Module Replacement . Did you complete the replacement? | Go to Step 9 | --
8 | Important: Perform the program procedure for the ISU. Replace the ISU. Did you complete the replacement? | Go to Step 9 | --
9 |

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