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MID 128 PID 91 FMI 9Severity: Info

MID 128 PID 91 FMI 9: Accelerator Pedal Position - Update Rate (Volvo)

Quick Answer

When MID 128 PID 91 FMI 9 sets, the ECM is indicating a fault condition involving the component or system named in the code.

OEM definitions and thresholds can vary, so confirm the exact meaning with service information or a capable diagnostic tool.

Code
MID 128 PID 91 FMI 9
Severity
Info
Applies to
Check OEM application
Can I drive?
The immediate driving effect of MID 128 PID 91 FMI 9 depends on whether the fault is active, the component involved, and any companion codes. If it repeats after clearing, diagnose it as an active fault rather than continuing to reset it.

Common Symptoms

  • N/A - diagnostic information only

Likely Causes

  • Missing signal from VECU
  • J1708 pedal information not available

Quick Diagnostic Checks

Check first
  1. 1Scan for companion codes and record freeze-frame data (if available).
  2. 2Inspect connectors, harness rub points, and pins for corrosion.
  3. 3Check for other active faults that may be upstream causes (communications, sensors, air/fuel issues).
  4. 4After repair, clear codes and confirm the fault stays inactive after a drive cycle.

Common Fixes

  • Check VECU for fault codes
  • Verify accelerator pedal sensor operation
  • Inspect J1708 data link communication
  • Check VECU power and ground
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FitmentsMeaningHow it worksImagesDetailed guideOEM/Engine notesLocation hintScan tool checksStep-by-step diagnosticDecision guideMisdiagnosisDerate/inducementChecklistToolsPreventionCommunity discussionsCommunity videosCommunity notesShare

What does MID 128 PID 91 FMI 9 mean?

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When MID 128 PID 91 FMI 9 sets, the ECM is indicating a fault condition involving the component or system named in the code.

OEM definitions and thresholds can vary, so confirm the exact meaning with service information or a capable diagnostic tool.

Treat repeat faults as ACTIVE and diagnose using live data, wiring checks, and basic inspections before replacing parts.

How this system works (why MID 128 PID 91 FMI 9 happens)

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Most modern fault logic is based on expected versus actual sensor readings, timing windows, circuit checks, and plausibility tests.

A stored code can come from a temporary event, while a repeatable active code gives you a much better diagnostic target.

The goal is to identify whether the failure is electrical, mechanical, sensor-related, or caused by another upstream fault before replacing components.

Detailed guide for MID 128 PID 91 FMI 9

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MID 128 PID 91 FMI 9 - Accelerator Pedal Position

**Fault Type:** Abnormal update rate

Fault Condition

  • Missing signal from VECU

Possible Symptoms

  • N/A - diagnostic information only (no performance symptoms noted in documentation)

Possible Causes

  • J1708 pedal information not available
  • Communication failure between VECU and EMS
  • VECU not broadcasting accelerator pedal position

System Information

The Vehicle Electronic Control Unit (VECU) directly monitors the Throttle Position (TP) Sensor located above the accelerator pedal. The VECU broadcasts this information on the serial data lines to other ECUs.

Diagnostic Tips

1. Check VECU for fault codes related to accelerator pedal

2. Verify accelerator pedal sensor operation with diagnostic tool

3. Inspect J1708 data link wiring and communication

4. Check VECU power and ground connections

5. Monitor accelerator pedal position data in VECU with Premium Tech Tool (PTT)

Location hint for MID 128 PID 91 FMI 9

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Component location varies by OEM and chassis. Use your engine’s service manual to confirm the sensor/valve location before replacing parts.

Tip: Inspect connectors and harness routing before replacing parts.

Scan tool checks for MID 128 PID 91 FMI 9

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  • Check status: ACTIVE vs INACTIVE / stored and review freeze-frame data when available.
  • Record companion codes and diagnose the earliest or most upstream fault first.
  • Compare live sensor values with expected operating conditions and inspect wiring and connectors.
  • Clear and re-test under similar conditions only after completing the initial inspection.

If your tool can’t run actuator tests, you can still diagnose a lot with careful inspection + repeatability testing.

Step-by-step diagnostic for MID 128 PID 91 FMI 9

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  1. Visual inspection (fast wins). Harness routing, connector pins, hoses/lines (if applicable), and obvious damage.
  2. Check fluid sanity. Not applicable unless your fault is fluid-related. Focus on inspections + repeatability.
  3. Confirm the fault is ACTIVE. Stored-only faults can be old events.
  4. Review live data and circuit values. Use OEM diagnostic software (examples: Cummins INSITE, Detroit DDDL, PACCAR DAVIE4) or a capable heavy-duty scan tool to review the affected signal, commanded/actual values when applicable, and related sensor data.
  5. Verify after repair. Clear codes, road test, confirm it stays inactive.

Decision guide (fast path) for MID 128 PID 91 FMI 9

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  • If the fault is STORED only → inspect, clear, and monitor. If it returns, treat it as active.
  • If ACTIVE → inspect the named component, connector, harness, supply/ground, and live-data plausibility.
  • If multiple codes are present → diagnose the earliest or most upstream code first.

Common misdiagnosis mistakes for MID 128 PID 91 FMI 9

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  • Replacing sensors or components without checking wiring, grounds, connector fitment, and companion codes.
  • Clearing the fault repeatedly without confirming whether it is ACTIVE and repeatable.
  • Missing an upstream fault that is causing the displayed code as a secondary symptom.

Will MID 128 PID 91 FMI 9 cause derate or inducement?

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This fault may not require immediate shutdown, but repeated or active faults should still be diagnosed.

Exact behavior depends on ECM calibration and which companion faults are active.

“Do this first” checklist for MID 128 PID 91 FMI 9

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  • Scan for companion codes and record freeze-frame data (if available).
  • Inspect connectors, harness rub points, and pins for corrosion.
  • Check for other active faults that may be upstream causes (communications, sensors, air/fuel issues).
  • After repair, clear codes and confirm the fault stays inactive after a drive cycle.

Tools needed to diagnose MID 128 PID 91 FMI 9

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  • Basic hand tools + good lighting for inspection
  • Multimeter for connector/power/ground checks (if wiring suspected)
  • OEM diagnostic software (examples: Cummins INSITE, Detroit DDDL, PACCAR DAVIE4) (or equivalent scan tool) for live data and supported diagnostic tests

Prevention tips to avoid repeat MID 128 PID 91 FMI 9

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  • Fix small wiring/connector issues early before they become repeat faults.
  • During service, inspect harness routing and clamp points near heat/vibration.
  • Don’t ignore intermittent faults. “Erratic” usually gets worse.

What to check first for MID 128 PID 91 FMI 9

  1. Inspect connectors and harness near the affected component for corrosion, rubbing, or loose pins.
  2. Check for upstream causes (communications, sensors, air/fuel issues).
  3. Check for other active faults that may be upstream causes (communications, sensors, air/fuel issues).

If the fault repeats after clearing, diagnose it as ACTIVE and review companion codes and live data before replacing parts.

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Mechanic community notes for MID 128 PID 91 FMI 9

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