Code Details
| Display code | WABCO RSSplus SID 3 FMI 8 |
|---|---|
| SPN | Not applicable or not verified |
| FMI | 8 |
| OEM code | WABCO / ZF SID 3 FMI 8 |
| Manufacturer | WABCO / ZF |
| System | Trailer ABS / RSSplus |
| Component | Wheel Sensor c |
| Source address | Unknown or not applicable |
| Severity | high |
| Review status | ai source checked |
| Source confidence | high |
| Last reviewed | 2026-04-09 |
Plain-English Meaning
This code reflects an ABS system performance observation rather than a conventional sensor wiring fault. The ECU determined that wheel C was slipping — rotating significantly faster or slower than expected for the vehicle's estimated speed — beyond what a normal ABS event would produce. This can reflect a genuine wheel-slip condition during extreme braking, but it can also indicate an ABS calibration or sensor speed-ratio mismatch.
WABCO MM-0888 FMI 8 is listed as 'excessive wheel slip indication' for Wheel Sensor c. Unlike FMI 2 (erratic signal), FMI 8 reflects a plausible speed signal that nonetheless deviates from expected behavior relative to the other wheel speeds in the system. The RSSplus ECU compares individual wheel speeds across all monitored channels; a significant deviation triggers FMI 8.
Common Symptoms
- Trailer ABS lamp may activate during heavy braking events or after an ABS activation sequence
- Wheel C speed reading diverges from other sensor readings in WABCO PC diagnostics
- More likely to appear during low-traction conditions, steep grades, or emergency braking events
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Genuine wheel lockup or excessive slip during hard braking — the ABS activation may not have prevented the slip
- Tire size mismatch on the affected axle that causes one wheel to read a significantly different speed than the others
- Tone ring tooth count mismatch between the affected wheel and the ECU calibration
- Sensor or tone ring issue that causes incorrect speed reporting, misinterpreted as slip
First Checks
- Check the tire sizes on the axle at position C against the other axle wheels — a different effective rolling radius will produce a persistent speed differential.
- Review recent brake event history in WABCO PC diagnostics to determine whether FMI 8 correlates with specific braking events or is set during normal operation.
- Inspect for locking or dragging brake components on the affected axle that could force the wheel to rotate slower than expected.
- If no physical cause is found, verify the tone ring tooth count matches the ECU configuration.
Can I Keep Driving?
Trailer ABS and brake-related codes should be handled conservatively. Stop safely for brake warnings, red stop lamps, abnormal braking, wheel-end concerns, or any severe warning condition, and follow fleet or OEM guidance.
Related Lookup Pages
Sources
- WABCO RSSplus Trailer ABS Maintenance Manual MM-0888 WABCO / ZF Commercial Vehicle Solutions · oem · accessed 2026-05-05 · confidence high
Source: WABCO / ZF Commercial Vehicle Solutions, WABCO RSSplus Trailer ABS Maintenance Manual MM-0888. 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 RSSplus SID 3 FMI 8 mean the ABS system failed during a braking event?
Not necessarily. FMI 8 flags that the ECU detected a wheel-slip condition that exceeded its threshold. This can happen during a severe braking event where ABS activated but the wheel still slipped beyond normal. It does not automatically indicate an ABS system failure — review the event history in WABCO PC diagnostics to determine context.
Can mismatched tires cause WABCO RSSplus SID 3 FMI 8 to set during normal driving?
Yes. If a tire with a significantly different diameter is mounted on one axle position, the ECU will see a consistent speed differential between that wheel and the others during any vehicle motion. This can trigger FMI 8 without any actual wheel slip.
Will WABCO RSSplus SID 3 FMI 8 set every time there is an ABS activation?
Normal ABS activations involve controlled wheel speed modulation and do not typically set FMI 8. FMI 8 is triggered when the slip ratio exceeds the ECU's upper threshold — a condition that is more severe than the normal ABS modulation range.