OBD-II code · Chassis
C0078 Tire Diameter
Detected wheel speed implies tire diameter outside expected range — typically wrong tire size or mismatched tires.
Is it safe to drive with C0078?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyWrong tire size or mismatch
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
- 0.5–2 h
- Emissions test
- Usually unaffected
- After the fix
- A drive cycle is needed before the light stays off
- Parts involved
- Tires
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.