WABCO MM-0112 SPN 789 FMI 2 – Left Front WSS wheel-speed sensor data erratic,

Code Details

Plain-English Meaning

This WABCO ABS code flags erratic, intermittent, or incorrect data from the left-side front axle wheel speed sensor — FMI 2 means the signal is present but inconsistent or implausible. The ABS ECU is receiving something from the sensor, but the signal pattern doesn't match what a normally installed, undamaged sensor and tone ring would produce at the measured wheel speed. Erratic signals point to tone ring issues, bearing play, or high-resistance connections rather than a simple open or short.

The WABCO MM-0112 table maps SPN 789 FMI 2 and SID 1 to Left Front WSS / wheel-speed sensor data erratic, intermittent, or incorrect. This page paraphrases the factual mapping and does not reproduce WABCO troubleshooting procedures.

Common Symptoms

• ABS warning lamp active, sometimes intermittent depending on vehicle speed and road surface
• Erratic or implausible speed reading at the left-side front axle wheel channel in WABCO diagnostic software
• May be more noticeable at certain speed ranges or on rough road surfaces
• Related stability or traction control events may accompany if equipped

Possible Causes

Possible causes may include the items below. The list is not a parts diagnosis.

• Tone ring with a damaged, missing, or uneven tooth producing a non-uniform signal pattern
• Excessive bearing play allowing the tone ring to wobble relative to the sensor tip, producing an amplitude-varying signal
• Partial sensor coil degradation producing an inconsistent output without fully failing
• High resistance at the wheel-end connector from corrosion or moisture, causing signal distortion without creating a full open
• Incorrect tone ring part or installation orientation producing the wrong pulse pattern for this ECU channel

First Checks

• Record the full code set, active status, and lamp state.
• Raise the wheel and slowly rotate it by hand while visually inspecting the tone ring: look for missing, cracked, or bent teeth and any debris packed into the ring slots.
• Check bearing play — grasp the wheel at 12 and 6 o'clock and push/pull; excessive play means the tone ring is not running true relative to the sensor.
• Inspect the wheel-end connector and harness for corrosion or high resistance that could distort the signal without creating a full open.
• Use WABCO TOOLBOX live data during a slow test drive to observe the signal waveform at this wheel position.

Can I Keep Driving?

ABS and brake-system codes are safety-related. Stop safely when the red stop lamp is on, braking feels abnormal, or stability control warnings are active. Do not bypass or disable brake or stability systems.

Related Lookup Pages

• FMI 2 explanation
• WABCO / ZF manufacturer hub
• ABS Light symptom page
• Brake Warning Light symptom page
• Search this code