For 1990-2009 cars
Data Link Communications Components
Data Link Connector Schematics
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The vehicle theft deterrent (VTD) system, called a Passlock II system, is designed to prevent vehicle theft by disabling the engine unless the Passlock lock cylinder is correctly engaged by a mechanical key. The Passlock II System utilizes the four following components for theft detection:

• | Lock cylinder

• | Ignition switch

• | Body control module (BCM)

• | Powertrain Control Module (PCM)

When the ignition switch is first turned ON, the body control module (BCM) will send a password to the PCM through the class 2 serial data circuit. If the BCMs password does not match the password that is stored in the PCM, the PCM will disable the engine. This will cause the engine to start and stall immediately or not start at all.

The SYSTEM telltale will flash on the IPC and the engine is disabled until a matching password is received. The password is checked every 4 seconds. The engine is disabled for at least 10 minutes and that the SYSTEM telltale will flash on the IPC for approximately 4 seconds then illuminate solid on the instrument panel cluster (IPC) for the 10 minutes for the following passwords received:

• | Fuel disabled

• | Undecided

• | Mismatched

The following are four situations in which the PCM and BCM passwords would not match:

• | PCM does not receive a password from the BCM (No communication between the BCM and PCM)

• | BCM sends a Fuel Disabled password, meaning a tamper has occurred.

• | BCM sends an Undecided password.

• | PCM receives a password (more than three invalid passwords are received other than Fuel Disabled or Undecided) from the BCM that does not match (swapped PCM or BCM).

After the vehicle has passed theft detection, the PCM will continue a normal engine operation. If the PCM loses the BCM communication within the same ignition cycle, the vehicle will continue to run on the following ignition cycles. This mode is called the fail enable mode. Additional information can be found in the Theft Deterrent section.

### Conditions for Setting the DTC

A password (other than the Fuel Disabled or Undecided password) that does not match is sent to the Powertrain Control Module (PCM) from the body control module (BCM).

### Action Taken When the DTC Sets

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

• | A history DTC stores.

• | The engine fueling is disabled by the PCM.

### Conditions for Clearing the MIL/DTC

• | As soon as one good (matching) passwords are received at key up (anything but a Fuel Disabled and Undecided password) this becomes a history code.

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

• | A scan tool can clear the DTCs.

### Diagnostic Aids

Attempting to start the vehicle by bypassing the Passlock ll system or by substituting parts without performing the password learn procedure may set a DTC P1631 and a P1632.

If no password is received, a DTC U1064 and P1632 may be set.

An intermittent may be caused by the following conditions:

• | Poor electrical terminal connection

• | Broken wire inside the insulation

Thoroughly check any suspected circuitry for the following items:

• | Backed out terminals or improper mating

• | Improperly formed or damaged terminals

• | Poor terminal to wiring connections

• | Physical damage to the wiring harness

• | Corrosion

### 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 malfunction occurred. The information is then stored in the scan tool for later reference.

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

3. The theft deterrent password resides in the Body Control Module (BCM). Anytime a VTD component is replaced, the Powertrain Control Module (PCM) must relearn the new BCM password. Refer to Password Learn .

4. Replacement PCMs must be reprogrammed. A reprogrammed PCM does not require the password learn procedure to be performed. The password will be learned on the first ignition cycle. Refer to the latest Techline information for programming procedures. The replacement PCM must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest Techline procedures for PCM reprogramming and the Crankshaft Position System Variation Learn abortion of the service manual for the Crankshaft Position Variation Procedure.

5. 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 On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn ON the ignition switch leaving the engine OFF.
2. Install a scan tool.
3. Check for any Body Control Module (BCM) DTC(s) with the scan tool.

Were any BCM DTC(s) set?

--

Go to Body Control Module System Check

Go to Step 3

3 | Check for any Passlock Theft Deterrent DTC(s) with the scan tool. Were any Passlock Theft Deterrent DTC(s) set? | -- | Go to Diagnostic System Check - Theft Deterrent | Go to Step 4
4 |

1. Perform the Password Learn Procedure. Refer to Password Learn .
2. Attempt to restart the engine.

Does the engine start and continue to run?

--

Go to Step 7

Go to Step 5

5 | Check for any new DTC(s) with the scan tool. Was any new DTC(s) set? | -- | Go to the applicable DTC table | Go to Step 6
6 |

1. Turn OFF the ignition switch.
2. Replace the PCM. Refer to the Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 7

--

7 |

1. Using the scan tool, clear DTCs.
2. Start the engine.
3. Idle the engine at normal operating temperature.
4. Operate vehicle within the conditions for running 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 table | System OK