B3033: How to Diagnose & Fix — Security System Indicates Tamper

The Passlock II theft-deterrent system reads a Hall-effect sensor and magnet in the ignition lock cylinder. As the sensor or lock cylinder wears, the BCM sees an out-of-range voltage, flags a theft fault, flashes the SECURITY light, and disables fuel injection so the engine cranks but won't start. Owners get stranded with a 'Service Theft System' or security light and a no-start that often clears after a wait. Extremely common and heavily searched on these trucks.

The HHR uses GM's Passlock theft-deterrent system, and a failing Passlock sensor in the ignition lock cylinder commonly triggers a false theft condition. The 'Service Theft Deterrent System' message appears, the security light flashes, and the engine cranks but will not start (or will not crank), often intermittently. A weak battery or a worn lock cylinder/sensor are the usual culprits.

The electronic steering column lock (ESCL) actuator in 2015-2020 Yukon XL models develops a clicking, popping, or grinding noise when turning the steering wheel, particularly at startup. In some cases, the ESCL prevents the vehicle from starting entirely, displaying a "Steering Column Lock" message. GM issued TSB 16-NA-012 acknowledging the issue. The ESCL motor gear teeth strip or the position sensor misreads, causing the lock to partially engage or fail to release.

The Passlock theft-deterrent sensor built into the ignition lock cylinder wears and sends an unstable resistance signal to the body control module, which then interprets a legitimate key as a theft attempt. The system disables the fuel injectors, leaving the car cranking but not starting with the SECURITY light flashing, and the failure typically recurs and worsens until owners are stranded repeatedly. This is one of the most widely documented complaints on the 1999-2005 Grand Am, with a 23+ page Edmunds thread and a RepairPal-confirmed pattern failure.

The 2000-2005 Bonneville uses GM's Passlock II immobilizer, which reads a Hall-effect sensor in the ignition lock cylinder housing rather than a chip in the key. The sensor and its hair-thin wiring at the column degrade, so the BCM sees a bad or missing signal, flashes the Security lamp, and disables the fuel injectors: the engine cranks, fires for a second, then dies, or does not fire at all. It is intermittent and worse in cold weather. Owners on the Pontiac Bonneville Club and GM Forum document the 10-minute relearn ritual (key on, wait until the security light stops flashing, three cycles) as the only way to get home; the earlier 1992-1999 cars used the different PASS-Key II resistor-pellet key and are not covered by this failure mode.