Summary
C0045 indicates the ABS module has detected a malfunction in the left rear wheel speed sensor circuit. The module cannot read a valid speed signal from the left rear wheel and disables ABS, traction control, and stability control as a result. The most common cause is a failed wheel speed sensor (30%), followed by wiring damage (30%) — rear sensor wiring runs a longer route and is vulnerable to undercarriage damage — and tone ring issues (20%). Standard brakes remain fully functional.
Severity: High — ABS and traction control are disabled
Safe to drive: Yes, with caution — normal brakes work but ABS and traction control are inactive
Repair cost: $50–$400 depending on cause
DIY difficulty: Easy to Moderate
What does C0045 mean?
The left rear wheel speed sensor is mounted at the rear hub or knuckle and reads a toothed reluctor ring that rotates with the wheel. The sensor generates an electrical signal proportional to wheel speed, which the ABS module uses to detect wheel lockup during braking and wheel spin during acceleration. The module continuously compares all four wheel speed signals to determine if any wheel is behaving differently from the others.
C0045 is triggered when the ABS module detects that the left rear wheel speed signal is absent, erratic, intermittent, or does not correlate with the other wheel speed inputs. Unlike front sensors, the rear sensor wiring typically runs along the underside of the vehicle or through the rear subframe area, making it susceptible to damage from road debris, exhaust heat, and corrosion.
On vehicles with integrated hub assemblies, the wheel speed sensor may be built into the hub bearing. In that case, sensor replacement requires replacing the entire hub assembly. On vehicles with separate sensors, the sensor bolts or presses into the rear knuckle and can be replaced independently.