For 1990-2009 cars

### Circuit Description

The ignition key contains a transponder that transmits a signal to the theft deterrent module when the ignition switch is turned to the ON position. The theft deterrent module compares the signal from the key and determines if an authorized key is being used. During this period, the engine control module (ECM) turns on the malfunction indicator lamp (MIL) by grounding the control circuit. The MIL control circuit is monitored by the theft deterrent module. When the theft deterrent module senses the voltage change from the ECM grounding the MIL control circuit, the theft deterrent module switches the signal on the VSS/theft deterrent signal circuit from the speed signal to send the frequency code to the ECM. The theft deterrent module sends the frequency code to the ECM on the same circuit used to transmit vehicle speed information to the ECM. The ECM compares the frequency code with the learned frequency code. If the frequency code sent by the theft deterrent module matches the frequency code programmed in the ECM, the ECM allows the engine to start. If the codes do not match, the ECM disables the injectors to prevent the engine from starting.

### Conditions for Running the DTC

Engine cranking

### Conditions for Setting the DTC

• | The frequency code in the ECM does not match the code received from the theft deterrent module.

• | The transponder signal from the key was incorrect or not present.

### Action Taken When the DTC Sets

The ECM will not illuminate the malfunction indicator lamp (MIL).

The engine will not start or may start and stall.

### Conditions for Clearing the MIL/DTC

• | The DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other non-emission related diagnostic.

• | The scan tool clears the MIL/DTC.

### Test Description

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

1. The wrong ignition key, the use of a key without a transponder, or an incorrectly programmed theft deterrent module will cause this DTC to set. Any of these faults will set a DTC in the theft deterrent module. The Diagnostic System Check for the theft deterrent system will direct you to the appropriate service information for any of these concerns.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Perform Diagnostic System Check - Theft Deterrent in Theft Deterrent.
2. Diagnose and repair any DTCs stored in the theft deterrent module.

Did you find and repair a DTC for the theft deterrent module or system?

--

Go to Step 5

Go to Step 3

3 |

1. Attempt to reprogram the ECM with the correct frequency code. Refer to Engine Control Module Replacement/Programming for the programming instructions.
2. Attempt to start the vehicle.

Does the DTC reset?

--

Go to Step 4

Go to Step 6

4 | Important: This vehicle is equipped with a theft deterrent system that interfaces with the ECM. Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle. Replace the ECM. Refer to Engine Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 5

--

5 |

1. Use the scan tool in order to clear the DTCs.
2. Select DTC and the Specific DTC function.
3. Enter the DTC number that was set.
4. Attempt to start the engine.

Does the scan tool indicate that the diagnostic Passed?

--

Go to Step 6

Go to Step 2

6 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK