Code Details
| Display code | WABCO MM-0112 SPN 794 FMI 2 |
|---|---|
| SPN | 794 |
| FMI | 2 |
| OEM code | WABCO / ZF SID 6 |
| Manufacturer | WABCO / ZF |
| System | ABS / ESC |
| Component | Right Third Axle WSS |
| Source address | Unknown or not applicable |
| Severity | high |
| Review status | ai source checked |
| Source confidence | high |
| Last reviewed | 2026-03-31 |
Plain-English Meaning
This WABCO ABS code flags erratic, intermittent, or incorrect data from the right-side third 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 794 FMI 2 and SID 6 to Right Third Axle 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 right-side third 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
Sources
- WABCO ABS and E Version Hydraulic ABS Maintenance Manual MM-0112 WABCO / ZF Commercial Vehicle Solutions · oem · accessed 2026-05-05 · confidence high
Source: WABCO / ZF Commercial Vehicle Solutions, WABCO ABS and E Version Hydraulic ABS Maintenance Manual MM-0112. This page paraphrases factual fields only and is not a substitute for the original document.
Open source - TOOLBOX PLUS Diagnostic Software ZF Commercial Vehicle Solutions · oem · accessed 2026-05-05 · confidence medium
Source: ZF Commercial Vehicle Solutions, TOOLBOX PLUS Diagnostic Software. This page paraphrases factual fields only and is not a substitute for the original document.
Open source
FAQ
Does FMI 2 on a WABCO WSS indicate a bearing problem?
Not exclusively, but it is one of the causes. Excessive bearing play allows the tone ring to oscillate relative to the sensor, which distorts the signal waveform. If you find no tone ring damage and the sensor checks out electrically, evaluating wheel bearing end play is a reasonable next step.
Is FMI 2 more or less serious than FMI 5 (open circuit)?
Both disable accurate ABS speed sensing at the affected wheel, which affects ABS braking performance. FMI 2 may be slightly more nuanced to diagnose because the sensor is sending a signal — just an unreliable one. Neither should be left unrepaired if ABS function is needed.
Can road vibration cause FMI 2 intermittently without an actual fault?
Normal road vibration does not typically cause FMI 2 on a healthy wheel end. If the code appears only on rough roads, it often points to a marginal tone ring condition or a bearing with borderline play that worsens under dynamic load.