OBD-II code · Chassis
C0399 4WD Mode Switch Circuit Malfunction
The transfer case or 4WD control module has detected an invalid signal from the driver-operated 4WD mode selector. Mode requests from the dashboard may be ignored.
Is it safe to drive with C0399?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyMode selector switch failed
- PossibleWiring or connector fault
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
Repair at a glance
- Difficulty
- Easy
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.3–1.5 h
- Emissions test
- Usually unaffected
- Parts involved
- Mode Selector Switch, Transfer Case Module, Switch Wiring
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.