Code Details
| Display code | WABCO RSSplus SID 6 FMI 2 |
|---|---|
| SPN | Not applicable or not verified |
| FMI | 2 |
| OEM code | WABCO / ZF SID 6 FMI 2 |
| Manufacturer | WABCO / ZF |
| System | Trailer ABS / RSSplus |
| Component | Wheel Sensor f |
| Source address | Unknown or not applicable |
| Severity | high |
| Review status | ai source checked |
| Source confidence | high |
| Last reviewed | 2026-04-09 |
Plain-English Meaning
The trailer ABS controller is receiving an irregular, inconsistent signal from sensor F — not a flat-line loss (which would be FMI 5) but a signal that fluctuates irregularly in a way the ECU cannot use reliably. Intermittent connector contact, harness damage that creates partial continuity, tone ring damage with missing or damaged teeth, and electromagnetic interference from nearby wiring are the most common causes.
WABCO MM-0888 FMI 2 flags an erratic or incorrect signal from Wheel Sensor f. The ECU's signal validation detects inconsistencies in frequency, amplitude variation, or missing pulses that do not match the expected sinusoidal or digital output for the sensor type. Unlike FMI 12 (non-plausible frequency), FMI 2 typically indicates intermittent rather than systematic deviation.
Common Symptoms
- Trailer ABS lamp on or intermittently blinking — may correlate with road vibration or connector flex
- Wheel sensor F shows irregular waveform or missing pulses in WABCO PC diagnostics
- Code may be intermittent or road-speed dependent if the cause is vibration-induced connector contact
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Intermittent connector contact at the sensor or at a harness junction — most common cause of erratic signal
- Tone ring at position F has missing, damaged, or unevenly spaced teeth causing irregular pulse output
- Harness chafed against a frame member, creating partial short that affects signal quality under vibration
- Electromagnetic interference from other trailer electrical circuits near the sensor wiring
First Checks
- Retrieve WABCO RSSplus SID 6 FMI 2 with WABCO PC diagnostics and check whether it sets as active or intermittent.
- Wiggle-test the sensor harness and connector while monitoring signal in live data — a connector that breaks contact under flexing will show in real-time.
- Inspect the tone ring at position F for missing or damaged teeth, rust buildup, debris, or physical impact marks.
- Inspect harness routing for chafing points against the trailer frame, suspension components, or slack adjuster travel path.
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
How is WABCO RSSplus SID 6 FMI 2 (erratic signal) different from FMI 10 (signal dropout)?
FMI 2 indicates the signal is present but inconsistent — it fluctuates erratically rather than cutting out completely. FMI 10 indicates a dropout where the signal disappears for a period and then returns. In practice, an intermittent connector can cause both, but FMI 2 more often points to partial contact or interference rather than complete momentary loss.
Can a damaged tone ring cause FMI 2?
Yes. A tone ring with missing teeth, deeply rusted peaks, or physical deformation will produce an irregular pulse pattern that the ECU cannot validate as consistent with wheel rotation. If the sensor wiring checks out, a thorough tone ring inspection is warranted.
Does this code clear itself after the issue is fixed?
Active or pending codes set by erratic signal conditions typically clear once the ECU receives a consistent, valid signal across a defined operating period. Some conditions may require a WABCO PC diagnostic reset after repair to confirm the code has cleared.