For 1990-2009 cars
Engine Controls Components
Cell 21: Power, Ground, MIL, and DLC
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The vehicle theft deterrent system, is designed to prevent vehicle theft by disabling the engine unless the lock cylinder is correctly engaged by a mechanical key. The theft deterrent system utilizes four components for theft detection, the lock cylinder, ignition switch, the Body Function Controller (BFC) and the Powertrain Control Module (PCM).

When starting the engine, the PCM looks for a password from the Body Function Controller (BFC) through the Class II serial data circuit. If the password is not recognized or not present, the PCM will disable the engine. There are two modes of tamper detection:

• | No Password Received - Engine will start and stall quickly. THEFT SYSTEM telltale will flash on the IPC.

• | Incorrect or Disable Password Received - (More than three invalid passwords are received) - The engine is disabled for at least 10 minutes and the THEFT SYSTEM telltale will illuminate solid on the Instrument Panel Cluster (IPC) for the 10 minutes.

After the vehicle has passed theft detection, the PCM will continue normal engine operation. Additional information can be found in Theft Deterrent Systems .

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

• | An unrecognized or no password is sent to the PCM from the BFC.

• | The conditions is present for less than 1 second.

### Action Taken When the DTC Sets

• | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.

• | A history DTC is stored.

• | Engine fueling is disabled by the PCM.

### Conditions for Clearing the MIL/DTC

• | A history DTC will clear after 40 consecutive warm up cycles without a fault.

• | DTCs can be cleared by using a scan tool.

### Diagnostic Aids

Attempting to start the vehicle by bypassing the theft deterrent system or substituting parts without performing the password learn procedure may set a DTC P1631.

If no password is received a DTC P1610, P1626 and P1630 may be set.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Any circuitry, that is suspected as causing an intermittent complaint, should be thoroughly checked for the following items:

• | Backed out terminals or improper mating.

• | Broken locks.

• | Improperly formed or damaged terminals.

• | Poor terminal to wiring connections.

• | Physical damage to the wiring harness.

• | Corrosion.

If the serial data loss occurred after a good theft password has been received, the PCM must be reprogrammed and the password learn and the crankshaft position variation learn procedures must be completed to allow the theft system to operate properly. Refer to Powertrain Control Module Replacement/Programming and Crankshaft Position System Variation Learn and Body Control Module (BCM) Programming/RPO Configuration for reprogramming procedures.

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table:

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. The scan tool can display whether or not the BFC has received and learned the password from the lock cylinder. If the password is not received, the reason the PCM set this DTC may due to a password that has not yet been learned due to a component being replaced, or a problem in the BFC or a VTD component.

3. The theft deterrent password resides in the Body Function Controller (BFC). Anytime a VTD component is replaced, the Powertrain Control Module (PCM) must learn the new BFC password.

4. A BFC Passlock theft deterrent DTC being set indicates that a theft deterrent component may be malfunctioning. Refer to the applicable BFC table for diagnosis.

5. If no vehicle theft deterrent DTCs were set and the BFC has not learned (received) a password from the ignition lock cylinder, the BFC may need to learn the password or be malfunctioning.

6. Replacement PCMs must be programmed. A reprogrammed PCM does not require the password learn procedure to be performed. The password will be learned on the first ignition cycle. The replacement PCM must be programmed and the crankshaft position system variation procedure must be performed.

7. If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.

#### DTC P1631 - Incorrect Security Password

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain OBD System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Display the data list for the BCM. Does the scan tool indicate that the Passlock data is Valid? | -- | Go to Step 3 | Go to Step 4
3 |

1. Perform the Password Learn Procedure in Password Learn Procedure portion of the service manual.
2. Attempt to restart the engine.

Does the engine start and continue to run?

--

Go to Step 7

Go to Step 6

4 | Are any Passlock theft deterrent DTCs set? | -- | Go to Diagnostic System Check - Theft Deterrent | Go to Step 5
5 | Refer to the Passlock Theft Deterrent portion of the service manual. Is the action complete? | -- | Go to Step 7 | --
6 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 7 | --
7 |

1. Using the scan tool, clear DTCs.
2. Start engine and idle at normal operating temperature.
3. Operate vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

--

Go to Step 8

Go to Step 2

8 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC | System OK