DTC P1631 Theft Deterrent Fuel Enable Signal Not Correct. Chevrolet PJJ 2000

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:

• | The lock cylinder

• | The ignition switch

• | The body control module (BCM)

• | The 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 will be disabled until a matching password is received. The password is checked every 4 seconds. The engine is disabled for at least 10 minutes and the SYSTEM telltale flashes on the IPC for approximately 4 seconds The telltale then illuminates continuously on the instrument panel cluster (IPC) for 10 minutes for the following passwords received:

• | Fuel disabled

• | Undecided

• | Mismatched

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

• | The PCM does not receive a password from the BCM -- This means that the BCM is not communicating with the PCM.

• | The BCM sends a Fuel Disabled password, indicating that tampering has occurred.

• | The BCM sends an Undecided password

• | The PCM receives more than three invalid passwords from the BCM, other than Fuel Disabled or Undecided passwords. This ordinarily occurs when the PCM or BCM has been replaced

After the vehicle has passed theft detection, the PCM will continue normal engine operation. If the PCM loses communication with the BCM during the same ignition cycle, the vehicle will continue to run during subsequent 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 PCM from the BCM.

### Action Taken When the DTC Sets

• | The PCM will record the 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 fuel system is disabled by the PCM.

### Conditions for Clearing the MIL/DTC

• | As soon as one good, or matching, password is received at key-up this becomes a history code. A good password is anything but a Fuel Disabled or Undecided password.

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

• | Use a scan tool to 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:

• | A faulty electrical terminal connection

• | A 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

• | Faulty terminal-to-wire connections

• | Physical damage to the wiring harness

• | Corrosion

### Test Description

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

1. A BCM passlock theft deterrent DTC being set indicates that a Passlock II component may be malfunctioning.

2. 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.

3. 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.

4. 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 | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you the Powertrain On-Board Diagnostic (OBD) System Check? | -- | 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) DTCs with the scan tool.

Were any BCM DTCs set?

--

Go to Diagnostic System Check - Body Control System in Body Control System

Go to Step 3

3 | Observe the BCM for any passlock theft deterrent DTCs with the scan tool. Were any passlock theft deterrent DTCs set? | -- | Go to Diagnostic System Check - Theft Deterrent in 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 DTCs with the scan tool. Was any new DTCs set? | -- | Go to the applicable DTC table | Go to Step 6

6

1. Turn OFF the ignition switch.

Important: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

2. Replace the PCM. Refer to the Powertrain Control Module Replacement .

Did you complete the repair?

--

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