B1600 B0xxx · Body (B) High severity
Immobilizer / Key Transponder Communication Fault
The immobilizer cannot read a valid key transponder, so the engine is prevented from starting. A no-start code, not a running fault.
Severity guidance: High — stop driving and diagnose now; risk of further damage
Symptoms you will notice
- Engine cranks but will not start
- Key symbol or immobilizer lamp flashing
- Starts with the spare key
Common causes
Ordered from most to least likely — start at the top.
- 1 Weak transponder key battery or damaged chip
- 2 Faulty antenna ring around the ignition
- 3 Immobilizer module fault
- 4 Recently replaced ECU not matched
How to diagnose it
Cheapest and least invasive first — most of these codes are not a parts problem.
- ✓ Try the spare key first — that immediately separates key from vehicle fault.
- ✓ Check for aftermarket devices near the ignition (tag tolls, metal fobs).
- ✓ Read the immobilizer ECU for antenna and transponder status.
- ✓ Verify ECU/immobilizer matching after any module replacement.
Repair options
- Program or replace the key
- Replace the antenna ring
- Re-match the ECU and immobilizer
B1600 — frequently asked questions
The spare key works — what is wrong? +
The first key's transponder or its housing. Replace and program it.
Can I bypass the immobilizer? +
Not legally or safely. Professional key programming is the correct fix.
Confirm the diagnosis before you buy parts
Send us the code, freeze-frame data and the vehicle — our engineers will tell you what to test first.