Code Details
| Display code | WABCO RSSplus SID 220 FMI 9 |
|---|---|
| SPN | Not applicable or not verified |
| FMI | 9 |
| OEM code | WABCO / ZF SID 220 FMI 9 |
| Manufacturer | WABCO / ZF |
| System | Trailer ABS / RSSplus |
| Component | Towing vehicle / trailer data link |
| 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 RSSplus ECU monitors communication with the towing vehicle and other trailer systems. SID 220 FMI 9 means data that should be arriving at the expected rate is not — the ECU has not received an update from the towing vehicle or a connected module within the required time window. This is an 'abnormal update rate' condition, meaning communication was established at some point but has become intermittent or slow.
WABCO MM-0888 SID 220 FMI 9 maps to a towing vehicle / trailer data link communication error. FMI 9 in J1939 and SPN/FMI systems is 'abnormal update rate' — a message that the ECU expects at regular intervals is arriving too slowly or too infrequently. In the trailer ABS context, this indicates that the RSSplus ECU is not receiving the expected tractor-side ABS status or speed reference messages at the correct rate.
Common Symptoms
- Trailer ABS communication warning on towing vehicle instrument panel
- SID 220 FMI 9 active in WABCO PC diagnostics
- Tractor-trailer ABS integration features (RSC, speed references) may be affected
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Intermittent 7-way connector contact on the blue ABS power circuit — connection drops interrupt the J2497 communication
- Towing vehicle ABS module not transmitting the expected messages — tractor-side ABS fault
- Incompatibility between the tractor's ABS system firmware and the RSSplus ECU's expected message format
- High resistance in the ABS power circuit creating communication dropout under load
First Checks
- Check the 7-way trailer connector and tractor socket for damaged or corroded pins — prioritize the blue ABS circuit.
- Check whether the towing vehicle has any ABS or data link fault codes active — a tractor-side communication issue can trigger SID 220 on the trailer.
- Test the trailer with a different tractor to determine whether the fault follows the trailer or stays with the original tractor.
- If the fault follows the trailer, inspect the ABS power circuit from the 7-way connector to the ECU for wiring or voltage issues.
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 SID 220 FMI 9 indicate a problem with the trailer or the tractor?
It can be either. The fault is on the data link between the tractor and trailer. Testing with a different tractor is the most efficient way to isolate which side has the issue — if the code clears with a different tractor, the original tractor's ABS system is the likely source.
Will the trailer ABS still work if SID 220 FMI 9 is active?
Trailer ABS function depends on the wheel speed sensors and the trailer ECU, not on tractor-trailer communication. Foundation ABS should still operate on the trailer. However, integrated functions that use tractor speed data as a reference may be affected.
Can this code appear when connecting to a tractor that does not have ABS?
Yes. If the RSSplus ECU expects to receive tractor ABS messages and the tractor does not send them — older tractors without ABS or without J2497 PLC capability — the ECU may log SID 220 FMI 9. This does not necessarily indicate a fault condition; it may reflect a compatibility or configuration difference.