C1278Irregular signal from the rear left wheel-speed sensor (test mode)
- Toyota/Lexus code · ABS / stability control
- Lights a warning lamp
- How the car detects it
- During the sensor check the rear left wheel-speed signal changed abnormally. This is a test-mode code: it only appears during the sensor check a workshop runs with a scan tool.
- What you may notice
- ABS warning light blinks in test mode
- Likely causes
- PossibleDamaged or dirty tone ring
- PossibleSensor installation
- RareSensor or wiring
- Sources
Backed by at least two independent sources.
From Obdaryn's Toyota/Lexus pack, exactly as the app shows it, with the public sources above. Guidance only; confirm with a workshop.