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.
Medium severity. Can I keep driving?Drive with caution and go to a repair shop. If it affects the brakes or steering, do not continue if you notice abnormal behavior.
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
Most likely causes
- ACC module internal fault
- Supply voltage out of range
- Module configuration invalid after part exchange
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
What each character of C0420 means
- C: Chassis
- 0: Generic code: same on every make
- 4: Subsystem depends on the code range
- 20: Specific fault in that system
Frequently asked questions
Can I keep driving with code C0420?
Drive with caution and go to a repair shop. If it affects the brakes or steering, do not continue if you notice abnormal behavior.
What causes code C0420?
The most common causes are: aCC module internal fault; supply voltage out of range; module configuration invalid after part exchange.
Sources
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.