Code Details
| Display code | WABCO RSSplus SID 156 FMI 2 |
|---|---|
| SPN | Not applicable or not verified |
| FMI | 2 |
| OEM code | WABCO / ZF SID 156 FMI 2 |
| Manufacturer | WABCO / ZF |
| System | Trailer ABS / RSSplus |
| Component | J2497 power-line carrier data link |
| Source address | Unknown or not applicable |
| Severity | medium |
| Review status | ai source checked |
| Source confidence | high |
| Last reviewed | 2026-04-09 |
Plain-English Meaning
The RSSplus system uses J2497 PLC communication — a technology that superimposes data signals on the trailer's power line — to exchange ABS information with the towing vehicle. FMI 2 means the ECU detected an irregular or erratic condition on this communication link. This is distinct from a complete communication loss (which would typically be FMI 9 or FMI 12). The signal is present but not behaving consistently.
WABCO MM-0888 SID 156 FMI 2 maps to a J2497 power-line carrier data link signal irregularity. J2497 (ISO 11992-1 for North American trailers) encodes data at a specific frequency and bit rate on the ABS power circuit. Signal irregularities can result from electrical noise on the trailer power supply, poor power line quality, termination issues on the PLC circuit, or interference from other trailer electrical systems that share the same power wire.
Common Symptoms
- Trailer ABS communication fault visible on towing vehicle ABS or instrument panel warning
- WABCO PC diagnostics shows SID 156 FMI 2 active
- Intermittent loss of ABS communication status between tractor and trailer
Possible Causes
Possible causes may include the items below. The list is not a parts diagnosis.
- Electrical noise on the trailer power supply line degrading the PLC signal quality
- Corroded or high-resistance 7-way connector pins on the blue (ABS) circuit
- Other trailer electrical loads (lighting, refrigeration, auxiliary power) creating interference on the PLC frequency
- Improper termination on the J2497 PLC circuit or a load connected to the ABS power wire that attenuates the PLC signal
First Checks
- Inspect the 7-way trailer connector — particularly the blue ABS circuit pin — for corrosion, damage, or poor contact with the tractor socket.
- Check the ABS power circuit wiring from the 7-way connector to the RSSplus ECU for voltage quality: measure voltage under load and look for excessive voltage drop.
- Identify any electrical loads connected to the ABS power circuit that should not be — only the ABS ECU should be on the blue ABS wire per SAE J560 assignment.
- If the tractor has an ABS status monitor for the trailer, note whether the communication fault correlates with specific road conditions, connector flex, or electrical load changes.
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
What is J2497 PLC and why does it use the power wire for data?
J2497 is the SAE standard for power-line carrier communication on North American trailer ABS systems. Rather than requiring a dedicated data wire, it superimposes a data signal on the blue (ABS) power wire in the 7-way trailer connector. This allows trailers to exchange ABS status information without an additional connector pin, but it means power quality and other loads on that wire can affect communication.
Can a bad 7-way trailer connector cause SID 156 FMI 2?
Yes. A corroded or damaged 7-way connector adds resistance to the ABS power circuit. This changes the impedance of the PLC communication path, which can degrade signal quality and cause FMI 2. The 7-way connector is the first point to inspect when PLC communication faults appear.
Does SID 156 FMI 2 mean the trailer ABS is not working?
FMI 2 is a communication irregularity, not a complete communication loss. ABS function may still be available on the trailer, but the towing vehicle may not be able to read or display the trailer's ABS status. A complete communication loss (FMI 9 or 12) would be a more severe condition.