Vehicles affected:
Chevrolet Malibu: 1997-’99 2.4L, 1997-2003 3.1L and 2004 Malibu 2.2L and 3.5L.

Symptom:
Vehicle will start and then stall. Security indicator on the dash is on. DTC P1626, P1630 and/or P1631.

Problem 1 of 3:
The Body Control Module (BCM) failed to recognize the signal from the ignition lock cylinder.

Test & Fix:
A scan tool should indicate a DTC P1626, P1630 or P1631 stored in the Powertrain Control Module (PCM). The flow chart for each code will direct a scan tool to be used to access BCM codes. This is the best way to perform diagnostics on this problem.

If using a scan tool that is not capable of retrieving BCM codes or viewing data, try the following procedure. Disconnect the wires from the ignition lock cylinder. Turn the ignition key to the Key On, Engine Off (KOEO) position. Using a voltmeter, check voltage on the white wire, at the BCM, to ground. The voltage should read 12 volts.

Then check the voltage on the yellow wire, at the BCM, to ground. This should read 5 volts. Next check the black wire, at the BCM, being sure there is a good ground on this wire.

If there is a loss of ground on the black wire or the voltage is missing on the white or yellow wires, check the power and ground for the BCM and the connections at the BCM. If powers, grounds and connections are OK, the BCM will need to be replaced.

Note: When you remove the BCM, first disconnect connector C3 before you disconnect the remaining connectors. When you re-install the BCM, connect connector C3 last. Connector C3 contains the BCM power and ground sources. If the voltages are correct, proceed to step 2.

Problem 2 of 3:
The ignition lock cylinder fails to change the voltage on the yellow wire.

Test & Fix:
With the ignition lock cylinder electrically reconnected, back-probe the yellow wire with the positive lead of the voltmeter and connect the negative lead to a known-good ground. Insert the ignition key in the lock cylinder, rotating the key to the start position, then release the key, allowing it to return to the KOEO position.

During the time the key was rotated to the start position then released to the KOEO position, the voltage on the yellow wire should change from 5 volts to a lower value. Because there are 10 different voltage values, we are unable to give a specific voltage value. However, what the voltmeter should indicate is a change in voltage value. If this change in voltage did not take place, replace the ignition lock cylinder. For the theft system relearn procedure, go to step 3.

Problem 3 of 3:
A component related to the theft system, BCM, PCM or ignition lock cylinder has been replaced and the password needs to be re-learned.

Test & Fix:
Password programming can be done using the following procedure:

1. Ensure the vehicle’s battery is fully charged.

2. Use a scan tool to clear any diagnostic trouble codes from the PCM and BCM.

3. Starting with the ignition switch in the Off position, momentarily crank the engine and leave the key in the Run position while observing the security indicator. In 10 minutes the security indicator should turn off. Rotate the key to the Off position for five seconds.

4. Repeat step 3 two more times.

5. The fourth time the engine is cranked, the engine should start and the BCM and PCM will have learned the new password.

6. Clear the BCM and PCM trouble codes again.

Courtesy of Identifix, Inc.