MIL Control Circuit Malfunction (Chevrolet)
What does P1661 mean?
The P1661 code means the vehicle's onboard diagnostic system has detected: MIL Control Circuit Malfunction (Chevrolet). This is a low severity code.
Common Symptoms
- Check Engine Light stays on constantly
- Check Engine Light does not illuminate during bulb check
- Instrument cluster warning light malfunction
- No other drivability symptoms
- MIL lamp flickering
Probable Causes (Ranked by Likelihood)
- Burned out MIL bulb in instrument cluster Very High
- Open circuit in MIL control wiring High
- Faulty instrument cluster circuit board Moderate
- PCM MIL driver circuit failure Low
Step-by-Step Diagnostic Procedure
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Verify whether the MIL illuminates during the key-on bulb check sequence.
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If the bulb does not light, check the bulb itself and its socket in the instrument cluster.
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Measure voltage at the MIL control wire at the instrument cluster connector with the PCM commanding the light on.
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Check for an open or short in the wiring between the PCM and instrument cluster.
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If wiring and bulb are good, test the instrument cluster and PCM MIL driver using a scan tool.
Frequently Asked Questions
Is P1661 a serious problem?
The code itself is low severity, but a non-functioning MIL means you could miss other important engine warnings. Fix it to ensure proper warning system operation.
Can I pass an emissions test with P1661?
No. Many states require the MIL to function properly during the bulb check as part of the OBD-II inspection.
Can I just replace the bulb myself?
In many GM vehicles, the MIL bulb is part of the instrument cluster and may require removing the cluster to access. Some models use LED elements that are not individually replaceable.