User question
MID 128 PPID 6 FMI 5
Artificial Intelligence Response
Direct answer to the question
- Meaning: MID 128 PPID 6 FMI 5 = Engine ECU (MID 128) has detected “current below normal or open circuit” (FMI 5) in the External Stopping Relay circuit (PPID 6). (otrperformance.com)
- Key points:
Detailed problem analysis
- What the ECU is flagging
- The ECU monitors the external stop input/relay line and expects to “see” relay-coil current (or a defined voltage on the stop input). FMI 5 sets when the ECU does not detect expected load/current—typical of a broken wire, unplugged/failed relay coil, or a connector/pin issue. (otrperformance.com)
- Circuit behavior and reference values (EMS2-based)
- In Volvo/Volvo Penta EMS2 documentation, the external stop input is brought to ECU connector A, pin A27. With the stop relay NOT activated, A27 sits around 0.8 × battery voltage; when the stop is activated, A27 rises to battery voltage. Abnormal low/no current or a short to ground elsewhere will deviate from these levels and can set FMI 5 (or FMI 4 for “voltage low”). (scribd.com)
- Typical root causes
- Open relay coil or wrong relay type (coil resistance too high).
- Harness open (broken conductor), corrosion, backed‑out pins at relay socket or ECU connector.
- Loss of relay coil power feed or ground.
- ECU driver/input fault (least common).
- Symptoms
- External emergency stop may not function; on some configurations, the engine may not start or may stop unexpectedly if the stop input is falsely asserted. (scribd.com)
Current information and trends
- Code formats: Many late-model heavy trucks still report legacy J1587 MID/PPID/FMI codes alongside J1939 SPN/FMI. FMI definitions (like FMI 5 = “current below normal/open”) are consistent across both diagnostics, which helps correlate symptoms in mixed fleets. (otrperformance.com)
- Platform note: Volvo Trucks, Mack, and Volvo Penta EMS2 literature all map PPID 6 to the external stopping relay, but pin numbering and whether the relay is fitted by default can differ by application/chassis. Always confirm using the exact service/wiring manual for your VIN/engine family. (scribd.com)
Supporting explanations and details
- Why FMI 5 appears: The ECU senses coil current (or inferred current from measured voltage at the input). An open circuit, excessive contact resistance, or loss of supply/ground makes measured current fall below a calibrated threshold, setting FMI 5. (otrperformance.com)
- Reference test point (EMS2 example): A27 ≈ 0.8×VBatt (not active) and ≈ VBatt (active). Any value near 0 V when not commanded, or floating/erratic voltage with the relay connected, indicates wiring/relay issues. (scribd.com)
- Typical relay coil metrics: 12 V automotive relays often have 70–160 Ω coils (≈75–170 mA). A coil reading OL (open) or a value several kΩ indicates failure.
Ethical and legal aspects
- The external stop is a safety function. Do not bypass, jumper permanently, or disable it to clear the code. That can create a safety hazard and may violate workplace safety regulations and company policies.
Practical guidelines
- Fast, structured troubleshooting (KOEO = key on, engine off)
- Visual inspection
- Locate the external stop relay and its connector; check for corrosion, moisture, heat damage, or loose terminals. Wiggle test the harness while monitoring the code status.
- Power and ground check at relay socket
- Verify coil supply feed (typically battery via fused source) and coil ground. Load-test with a 21 W test lamp or an appropriate load, not only a DMM, to reveal high-resistance faults.
- Coil resistance test
- Remove relay; measure coil resistance across the coil pins. Replace the relay if open or grossly out of spec.
- ECU-side signal verification
- Back-probe the stop input line. On EMS2, measure at A27:
- Not active ≈ 0.8×VBatt; active ≈ VBatt. Values near 0 V or drifting suggest short-to-ground or open harness. (scribd.com)
- Continuity from relay socket to ECU
- Perform ohmic checks (<1 Ω typical) and flex/wiggle harness to catch intermittents. Repair any opens/corrosion and replace loose terminals.
- Functional test
- Using the OEM diagnostic tool (e.g., Tech Tool/VIDA), command the stop function and watch A27 and relay operation. Substitute a known-good relay if needed.
- ECU assessment
- If wiring and relay are confirmed good and the command from the tool does not produce the expected voltage/current change, suspect ECU driver/input and follow the OEM decision tree before replacement.
- After repair
- Clear DTCs, cycle key power, verify the external stop works, and perform a short road test or run-up while monitoring live data.
Possible disclaimers or additional notes
- Manufacturer differences: Some online lists misidentify PPID 6 as a fuel pressure parameter. On Volvo/Mack/EMS2 systems, PPID 6 specifically denotes the external stopping relay; fuel pressure is typically PID 94/SPN 94, not PPID 6. Confusion often comes from mixing generic PID/SPN lists with OEM PPIDs. (id.scribd.com)
- Pinouts: The A27 detail applies to EMS2-based systems; other generations may use different pins—always verify with the correct wiring diagram. (scribd.com)
Suggestions for further research
- Provide your truck’s year, model (e.g., VNL, VHD), engine (D11/D13/D16), and last six of the VIN. With that, I can pull the exact wiring/pinout and the ECU test steps for your build.
- Consult the engine ECU/EMS2 Group 30 electrical manual relevant to your engine for definitive test values and schematics. (scribd.com)
Brief summary
- Your code points to an electrical open/low-current fault in the external stopping relay circuit monitored by the engine ECU. Check the relay coil, its power/ground, the harness and connector integrity to the ECU (EMS2 A27 in many Volvo/EMS2 systems), and only then suspect the ECU. This is a safety-related circuit—repair rather than bypass it. (otrperformance.com)
Disclaimer: The responses provided by artificial intelligence (language model) may be inaccurate and misleading. Elektroda is not responsible for the accuracy, reliability, or completeness of the presented information. All responses should be verified by the user.
