Ignition Switch Circuit Malfunction
There’s an issue with the ignition switch 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 ignition switch is either not sending the right signal to the computer when you turn the key, or there’s a wiring problem making it fail to start the engine or recognize it's on.
What the computer is actually seeing
The computer monitors the voltage coming from the ignition switch. In an active state (ignition on), it expects to see around 12V. If it’s less than 9V or more than 12.5V, or if there’s no change passing to the computer, it throws this code.
What a healthy reading looks like
Voltage at the ignition switch should be between 9V and 12.5V when the ignition is on.
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. Inspect the ignition switch and its wiring for corrosion, damage, or loose connections. Secure any loose connections and repair any damaged wires. If everything looks good, move to the next step.
- 22. Check the voltage at the ignition switch with a multimeter. Turn the key to the 'on' position and measure voltage. Are you getting between 9V and 12.5V? If yes, proceed. If no, replace the ignition switch.
- 33. With the ignition on, check the voltage at the corresponding wiring harness leading to the BCM. Is it receiving the correct voltage? If yes, the wiring is good; if no, trace the wiring back to find issues.
- 44. If both the switch and wiring are okay, test or replace the BCM as it may not be processing the signal correctly.
Common causes
- Faulty ignition switch
- Wiring issues or bad connections
- Blown fuse in the ignition circuit
- Bad body control module (BCM)
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
Not recommended. It can prevent the engine from starting, leaving you stranded.
Will this code come back after clearing it?
If the underlying issue isn’t fixed, it likely will.
Why does this code pair with U0100?
U0100 indicates loss of communication with the engine control module, which may happen if the ignition switch fails.
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