For 1990-2009 cars

### Circuit Description

The theft deterrent control module produces the theft deterrent fuel and starter enable signal when ignition is ON and the proper transponder key value is detected. The powertrain control module (PCM) monitors the fuel and starter enable signal during crank. If the proper signal is present on the Class 2 Serial Data Circuit, the PCM enables the fuel delivery and starter operation in order to allow the engine to start. If the PCM detects an incorrect password, vehicle theft deterrent (VTD) system failure or attempted vehicle theft, DTC P1631 is set. The engine will not start or crank as long as the condition is present.

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

The powertrain control module (PCM) detects an incorrect password from the theft deterrent control module.

### Actions Taken When the DTC Sets

• | The vehicle will not start.

• | The powertrain control module sends a serial data message to the IPC to illuminate the SECURITY indicator.

• | The PCM will not illuminate the malfunction indicator lamp (MIL).

• | The PCM will store conditions which were present when the DTC set as failure records data only. This information will not be stored as freeze frame data.

### Conditions for Clearing the MIL/DTC

• | A history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using a scan tool.

### Diagnostic Aids

DTC P1631 indicates that the PCM has detected an incorrect password from the theft deterrent control module. This condition can occur if an incorrect key is being used when attempting to start the vehicle or if the theft deterrent control module has been replaced and the PCMs password learn function has not been enabled.

### Test Description

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

1. To set this code, the password that the PCM has learned does not agree with the password being received from the theft deterrent control module. This condition can occur if the theft deterrent control module has been replaced andthe programming theft deterrent system components procedure has not been performed.

2. If the PCM resets the DTC after the programming theft deterrent system components procedure has been performed, the theft deterrent control module is malfunctioning.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Theft Deterrent System Schematics Connector End View Reference: Theft Deterrent System Connector End Views
1 | Did you perform the Theft Deterrent Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check - Theft Deterrent
2 | Important: If a 10 Minute or 30 Minute Re-Learn Procedure is performed, all keys not learned at that time will be erased and will not be recognized. Perform the Adding Keys procedure on all keys or instruct the customer how to perform the Adding Keys procedure. Refer to Adding Keys .

Perform the Programming Theft Deterrent System Components procedure. Refer to Programming Theft Deterrent System Components .

Is the procedure complete?

Go to Step 3

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3 |

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 4

System OK

4 | Important: If a 10 Minute or 30 Minute Re-Learn Procedure is performed, all keys not learned at that time will be erased and will not be recognized. Perform the Adding Keys procedure on all keys or instruct the customer how to perform the Adding Keys procedure. Refer to Adding Keys .

1. Replace the theft deterrent control module. Refer to Theft Deterrent Module Replacement .
2. Perform the programming theft deterrent system components procedure. Refer to Programming Theft Deterrent System Components .

Is the replacement complete?

Go to Step 5

--

5 |

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