Code Details
| Display code | WABCO MM-0112 SPN 794 FMI 3 |
|---|---|
| SPN | 794 |
| FMI | 3 |
| 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 the right-side third axle wheel speed sensor circuit reading above the expected voltage range. FMI 3 means the signal wire or sensor output is at or near supply voltage — which prevents the ABS ECU from reading a valid wheel speed signal. The most common causes are a sensor wire contacting a power source or a sensor with an internal short, though a connector fault can also pin the circuit high.
The WABCO MM-0112 table maps SPN 794 FMI 3 and SID 6 to Right Third Axle WSS / wheel-speed sensor circuit shorted to supply voltage. This page paraphrases the factual mapping and does not reproduce WABCO troubleshooting procedures.
Common Symptoms
- ABS warning lamp active, often immediately at key-on
- ABS disabled or partially disabled at the third axle — the ECU cannot read valid speed from this wheel
- WABCO TOOLBOX or ACOM diagnostic software will show the SPN/FMI and the affected wheel position
- Stability control (if equipped) may also report a related indicator
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Right Third Axle WSS signal or power wiring in contact with another power source — chafed insulation touching a battery, alternator, or ignition wire
- Sensor internal short: the sensor itself is creating a high-voltage condition on the signal line
- Corroded or water-contaminated connector at the sensor or at the ABS ECU harness connection pushing the signal high
- Recent wheel-end service or brake work that may have disturbed harness routing near the sensor
First Checks
- Treat ABS warnings as safety-related. Record the exact SPN/FMI, SID, active or stored status, and all related codes before any physical inspection.
- Disconnect the right-side third axle WSS connector and measure voltage between the signal wire and chassis ground with the key on — a high voltage reading (close to battery voltage) with the sensor disconnected confirms a wiring fault, not a sensor fault.
- Inspect the harness routing from the sensor to the ABS ECU connector for chafing against the frame, brake lines, or hot engine/exhaust components.
- If wiring checks out clean, measure sensor resistance across the sensor terminals with it disconnected — compare to the spec in WABCO service documentation; an out-of-range reading points to a failed sensor.
- Verify with WABCO TOOLBOX or ACOM software and qualified brake-system documentation before replacing components.
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 WABCO MM-0112 SPN 794 FMI 3 always mean the wheel speed sensor needs replacement?
Not necessarily. FMI 3 (shorted high) is often a wiring fault rather than a sensor fault — a wire in contact with a power source will create the same reading as a sensor with an internal short. Disconnect the sensor first and measure wiring voltage to separate the two before ordering a replacement sensor.
Will ABS still function on other wheels with WABCO MM-0112 SPN 794 FMI 3 active?
The ABS ECU typically isolates the fault to the affected wheel position. Other wheel channels that are reading correctly may continue to function, but the ABS system as a whole enters a partial or full disable state depending on the WABCO ECU configuration and fault severity. Do not rely on ABS being fully available with this code active.
Is it safe to drive with WABCO MM-0112 SPN 794 FMI 3?
Do not use this page as permission to continue driving. ABS faults are safety-related. Evaluate warning lamp color, brake behavior, and operating conditions — if the red stop lamp is on, braking feels abnormal, or you are in heavy traffic, stop safely. At a minimum, plan to have the fault diagnosed before the next loaded trip.