C0420
- Chassis
- Generic (SAE)
Not urgent
Unlikely to affect driveability. Worth resolving so the light does not mask a future fault.
Adaptive Cruise Control Module Internal Performance
This code is in our catalogue but has not yet been through editorial review, so the guidance below is limited to what our structured data supports. We publish deeper diagnostic content only after a code has been reviewed — here is why.
The adaptive cruise control module has reported an internal performance fault — for example self-test failure, supply voltage out of range or invalid configuration. ACC is disabled.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Unlikely to affect driveability. Worth resolving so the light does not mask a future fault.
- Urgency
- Not urgent
- Will it pass emissions
- Not affected
- Check engine light
- Varies
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | ACC module internal fault | Very common | — |
| 2 | Supply voltage out of range | Common | — |
| 3 | Module configuration invalid after part exchange | Occasional | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
- Acc Module
- Vehicle Power Supply
- Communication Bus
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Awaiting review
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