P1624: Immobilizer or SBDS Communication Fault
The P1624 code indicates that the Powertrain Control Module (PCM) has detected interactive codes from the Symptom-Based Diagnostic System (SBDS) or a failure in the anti-theft system's fuel enable signal communication. This typically means the PCM did not receive the correct security password from the Body Control Module (BCM) or the Immobilizer Control Module, preventing the engine from starting or running.
01. Most Common Causes
- Failed serial data communication (Class 2 / GMLAN) between BCM and PCM
- Faulty or incorrectly programmed Body Control Module (BCM)
- Damaged or unprogrammed ignition key/transponder
- Open, shorted, or high-resistance wiring in the communication circuit
- Faulty PCM or PCM needing reprogramming
- Low battery voltage or unstable voltage during startup
02. Symptoms You Will Notice
- Engine cranks but does not start
- Engine starts then immediately stalls
- Anti-theft warning light illuminated on the dashboard
- No communication with scan tool or intermittent communication
03. Step-by-Step Diagnosis
Verify battery voltage is stable and above 12.4 volts during cranking
Check for other related codes (e.g., U0100, U0101) indicating loss of communication
Inspect serial data wiring between BCM and PCM for damage, corrosion, or loose connections
Test the ignition key transponder using a compatible key programmer or scan tool
Attempt to reprogram the BCM and/or PCM with the correct security parameters
If all else fails, replace the BCM or PCM as needed and perform relearn procedures
1. Frequently Asked Questions
Is it safe to drive?▼
No, this code is high severity. The vehicle may not start or may stall unexpectedly, posing a safety risk. It should be repaired before driving.
How much does it cost to fix?▼
Repair costs typically range from $100 to $600, depending on the cause. A simple key reprogramming may be under $100, while replacing a BCM or PCM can cost $300–$600 or more.