Code
B1780
HUMMER
B — Body
Theft Lock Enabled
Views:
UK: 20
EN: 22
RU: 15
AI status
Completed
Completed
100%
Causes
- Immobilizer/theft deterrent system intentionally engaged (theft lock)
- Unrecognized or unprogrammed key/transponder
- Faulty or weak key fob/transponder battery
- Low vehicle battery or unstable voltage during key recognition
- Faulty theft deterrent module, BCM, or antenna ring
- Damaged wiring or poor ground to theft module/BCM
Symptoms
- Engine cranks but will not start, or no crank/no start condition
- Security indicator (theft) lamp illuminated or flashing on dash
- Remote entry or keyless start disabled or intermittent
- Starter disabled even with correct key
- Body/BCM features related to theft deterrent not functioning
- DTC B1780 stored in body/theft module or BCM
What to check
- Read all stored DTCs and freeze frame with a capable scan tool; note related codes
- Observe security/theft warning lamp behavior during key cycle
- Try a known-good/spare programmed key and check if code clears or behavior changes
- Check vehicle battery voltage (at rest and during cranking) and battery connections
- Verify fuses and power/ground at BCM and theft deterrent module
- Inspect wiring and connectors at ignition cylinder/antenna ring and theft module
Signal parameters
- Immobilizer status: ACTIVE / INACTIVE
- Key transponder ID read / match result (OK / FAIL)
- Key fob battery voltage (V)
- Starter enable command (sent/not sent)
- Fuel pump enable command (sent/not sent)
- BCM theft lock flag/parameter
Diagnostic algorithm
- Connect a diagnostic scan tool. Read and record B1780 and any other stored codes and freeze-frame data.
- Confirm security lamp behavior: cycle ignition and observe lamp sequence for normal or fault indications.
- Attempt to start with a known-good programmed key. If the vehicle starts, suspect key/transponder or key programming.
- Check key fob/transponder battery and replace if weak. Re-test key recognition.
- Measure vehicle battery voltage (12.4–12.8 V at rest). Verify proper voltage during key read and cranking; charge or replace battery if low.
- Inspect fuses, module power and ground, and connectors at the BCM and theft/immobilizer module. Repair any poor connections.
- Use the scan tool to view immobilizer/key ID parameters. If key not recognized, attempt key re-learn/programming per manufacturer procedure.
- Check antenna ring/read coil at the ignition switch for continuity and proper operation; replace if damaged.
- If communications errors present (CAN/U codes), diagnose and repair network wiring or modules before replacing theft components.
- If module fault confirmed or module fails self-tests, replace or reflash module per manufacturer procedures and reprogram keys as required.
- After repairs, clear codes and perform repeated start cycles and a road test to confirm the theft lock does not re-enable.
Likely causes
- Key transponder not recognized (worn or unprogrammed key)
- Weak key fob battery preventing proper identification
- Poor battery voltage at time of key read causing anti-theft activation
- Faulty immobilizer antenna ring or connector at ignition switch
- Loss of communications between theft module and BCM (CAN/fuse/ground)
- Stored theft lock state after multiple failed key attempts or attempted theft
Fault status
Status
Theft lock is enabled — immobilizer/security system has disabled normal start or operation. Stored in body/anti-theft module (B1780).
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Repair manuals
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138
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