Vehicle Security System Signal Circuit Failure
There's an issue with the vehicle's security system signal circuit.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The vehicle's computer isn't receiving or sending the right signals to the security system, which might prevent the vehicle from starting or locking properly.
What the computer is actually seeing
The body control module (BCM) expects a specific voltage level on the security signal circuit, usually around 2.5V when the system is active. If it sees 0V or doesn't receive the signal within 50 milliseconds, it'll trigger this code.
What a healthy reading looks like
Signal voltage should be around 2.5V; if it's below 1V or nonexistent, there's an issue.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check the wiring and connectors between the ignition switch and the BCM for visible damage or corrosion. If you find issues, repair them and retest.
- 22. Measure the voltage on the security signal circuit with the key in the ON position. It should read around 2.5V. If it's 0V or fluctuating, further investigation is needed.
- 33. Inspect the key fob or transponder for damage. Test with a spare key if available. If the spare works, replace the faulty key.
- 44. If wiring and fob check out, consider testing or replacing the BCM, as it may have failed.
Common causes
- Damaged wiring in the security signal circuit
- Faulty body control module (BCM)
- Bad connections in the security system connectors
- Faulty key fob or transponder
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not recommended to drive as the vehicle may fail to start or lock properly.
Will this code come back after clearing it?
If the underlying issue isn't fixed, yes, the code is likely to return.
Why does this code pair with B1620?
B1620 also relates to security issues, often indicating multiple points of failure in the security system.
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