Rick's Free Auto Repair Advice

GM Passlock Trouble Codes

This is one in a series of articles. READ THIS FIRST

GM made several different types of anti-theft systems. VATS, PassKey, and PassLock. The troubleshoot and reset procedures are different for each. PassLock seems to have the highest failure rate. So if you have a key WITHOUT a chip in it, chances are it’s a PassLock system. This article describes how to troublshoot and fix a PassLock system. But here are some more articles to help

Click here to see the resetting procedure for PassLock

Click here to see the trouble codes for a PassLock system

Click here to see a typical PassLock wiring diagram

IF you have a PassKEY system, click here to see the reset procedure

B2947: SHORT TO GROUND ON THE PASSLOCK SENSOR POWER CIRCUIT

The BCM sets this code if it sees a short to ground on the Passlock sensor power circuit (white wire) for one second. The test occurs with the ignition switch in the ACCESSORY, ON, or START position.

The BCM then sends a message to the instrument cluster to turn the SECURITY indicator ON steady. If the BCM detects the short to ground during while you’re trying to start the engine, it won’t send a coded message to the PCM and the PCM will not enable the fuel injectors. The engine will not start or will start and stall.

However, if the BCM detects the short to ground AFTER the engine has started, it will enter “fail-safe” mode. Next time you restart the BCM will send a password to the PCM to allow fuel injector operation and the engine will start.

If you fix the short to ground, cycle the ignition switch from OFF to ON. The BCM will then enter the code as a “history” code and store it there for the next 100 starts.

If you do NOT fix the short, you CANNOT clear the code.

B2948: SECURITY SENSOR SIGNAL CIRCUIT VOLTAGE HIGH

This code sets if the BCM detects battery voltage on the sensor circuit (yellow wire) for more than 1-sec AFTER the ignition switch has been turned to OFF. This is basically a short to battery from the sensor supply circuit (white wire) to the sensor circuit (yellow wire).

Test for a short to battery with the ignition switch in the OFF position.

If the BCM sees battery voltage with ignition turned to off, it will set this code and turn the SECURITY light on steady.

The BCM will still allow the car to start but will store the code and keep the SECURITY light on until it no longer detects short to battery. If you fix the short to battery, cycle the ignition switch from OFF to ON. The BCM will then enter the code as a “history” code and store it there for the next 100 starts.

B2957: SECURITY SENSOR SIGNAL CIRCUIT VOLTAGE LOW

The BCM will set this code if it detects sensor voltage (yellow wire) of less than .4-volts for 1-sec. after turning the ignition switch to CRANK/START. This is usually a sign of a poor connection. After you fix the connection, wait 10-mins for the tamper timer to expire.

The BCM will not allow the vehicle to start if it detects low voltage before you start the vehicle. The SECURITY light will flash for 10-mins, then turn on steady. If the vehicle is running when the BCM detects the fault, the BCM will enter “fail enable mode.” It will allow the vehicle to start and run, but the SECURITY light will remain on steady.

B2958: BCM SIGNAL INPUT VOLTAGE HIGH

The BCM will set this code if it sees signal input voltage (yellow wire) higher than 4.9-volts for 1-sec after turning the ignition switch to CRANK.

The BCM will enter fail enable mode and will allow the engine to start and run. The SECURITY light will be ON steady. The code will clear once the BCM senses normal voltage, but will store the code as a history code for the next 100 concurrent ignition cycles.

B2960: BCM READING A VALID BUT DIFFERENT CODE VALUE THAN PREVIOUSLY LEARNED

The BCM is expecting a certain voltage value from the sensor based on its last learn cycle. The BCM compares the voltage value to its stored value every time the ignition switch is rotated from ON to CRANK. If the BCM sees a different voltage value from the sensor, it will not send a coded message to the PCM and the vehicle will not start. The SECURITY light will FLASH.

If the vehicle is running when the BCM detects the incorrect voltage, it will enter fail enable mode and allow the vehicle to start and run and will turn the SECURITY light ON steady. The code will clear once the BCM senses normal voltage, but will store the code as a history code for the next 100 concurrent ignition cycles.

B3031: BCM IS IN LEARN MODE BUT DOES NOT SEE A VALID PASSLOCK™ SENSOR CODE

A new BCM is programmed to accept the first voltage value it sees from the sensor, providing that the value is within limits. The BCM will set this code if it is in learn mode but does not see a valid sensor voltage (yellow wire). The BCM will light the SECURITY light steady.

Once the BCM detects a valid voltage value from the sensor, the B3031 changes to history code.

B3033: PASSLOCK™ TAMPER

The BCM sets this code when it sees a voltage signal from the sensor (yellow wire) indicating a tamper situation during engine startup.

If the BCM is NOT in programming mode or fail enable mode, it will store B3033 in memory and flash the SECURITY light. It will send a message to the PCM to disable fuel delivery. The BCM will then stop sampling sensor readings for 10-mins. If the ignition switch is left on for at least ten minutes, the BCM then enters theft deterrent
re-learn mode.

However, if the BCM IS in programming mode or IS in fail enable mode the BCM will
store B3033 in memory and will turn on the SECURITY light steady. The BCM will send a message to the PCM to enable fuel delivery and will allow the engine to start and run.

P1626: LOSS OF THE STATE OF HEALTH

The PCM will set this code if the engine is running and the PCM detects a loss of the “state of health” serial data message from the IPC/BCM theft deterrent system.

The PCM will NOT light the Check Engine/Service Engine Soon light. It will store the conditions present when the code was set to inform the technician. The code will self clear if the PCM sees 40 consecutive starts without another malfunction.

P1630: THEFT DETERRENT PASSWORD LEARN MODE

This code will set if the PCM remains in theft deterrent password learn mode for more than 2 seconds. The PCM will not light the Check Engine/Service Engine Soon light. It will store the conditions present when the code set. This code can be cleared by a scan tool.

P1631: INCORRECT PASSWORD FROM THE VTD SYSTEM

The PCM sets this code if it receives an incorrect password from the IPC/BCM. It will light the Check Engine light and store the conditions present at the time the code was set.

DTC P1632: UNDECIDED PASSWORD SENT FROM BCM

The PCM will set this code if the ignition switch is ON and the PCM receives a fuel disabled password from the IPC/BCM or an UNDECIDED password is sent from the IPC/BCM. The PCM will store the conditions present at the time the code was set and will disable the fuel system and light the Check Engine light.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat


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