What it means
The module detects a left-rear wheel-speed reading that does not correlate with related wheel-speed signals. The code alone does not establish the cause.
At a glance
- Usually lights the ABS or stability-control warning light
- The engine or gearbox may go into limp mode
How it works
The ABS module compares the left-rear wheel-speed reading with the other wheels to check whether the readings agree during driving. C0511 sets when the left-rear speed does not track those related readings as expected; the mismatch can come from tire differences or a sensor, encoder, or circuit fault.
Common causes
Most likely first.
- Incorrect tire size or significantly different tire wear
- Damaged tone ring or encoder
- Faulty wheel-speed sensor
- Damaged wiring or connector
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
How to diagnose it
- Review freeze-frame data and graph all four wheel speeds during a cautious low-speed drive to see when the left-rear reading diverges.
- Check that all tires are the specified size and that the left-rear tire’s wear and pressure are reasonably consistent with the others.
- Inspect the left-rear sensor connector and wiring for corrosion, looseness, chafing, or damage.
- Inspect the left-rear tone ring or encoder for damage, contamination, or an uneven signal pattern as the wheel turns.
- Test the left-rear sensor and circuit, and check wheel bearing play that could disturb the sensor reading, using the manufacturer’s specifications.
Common fixes
- Correct an incorrect tire size or replace a mismatched, excessively worn tire.
- Clean and secure the left-rear sensor connector or repair its terminals.
- Repair damaged left-rear sensor wiring.
- Replace a faulty left-rear sensor or damaged tone ring/encoder.
Can I keep driving?
Drive cautiously and allow extra stopping distance because ABS or stability control may be limited, and brake assist behavior may be affected. Avoid hard braking and slippery conditions until the left-rear reading agrees with the other wheels.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.