Can I drive with MID 128 PID 81 FMI 2?

Usually yes for a short distance, but fix it soon. Warning faults like MID 128 PID 81 FMI 2 commonly escalate into torque derate if ignored. The scan-tool checks below help determine urgency.

How do I fix MID 128 PID 81 FMI 2?

Start with: Check sensor connections for looseness or corrosion. Then follow the diagnostic steps and scan-tool checks on this page.

What tools help diagnose MID 128 PID 81 FMI 2?

A quality J1939 scan tool and, when available, OEM diagnostic software (examples: Cummins INSITE, Detroit DDDL, PACCAR DAVIE4) for actuator tests and live data.

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Fitments Meaning How it works Images Detailed guide OEM/Engine notes Location hint Scan tool checks Step-by-step diagnostic Decision guide Misdiagnosis Derate/inducement Checklist Tools Prevention Community notes Share

Level: Warning

MID 128 PID 81 FMI 2: Particulate Filter - Signal Erratic (Volvo)

MID 128 PID 81 FMI 2: Particulate Filter - Signal Erratic (Volvo). Symptoms (1), causes (2), and fixes (3). What to check first to prevent derate and downtime.

Code	MID 128 PID 81 FMI 2
Severity	Warning
Applies to	Varies by OEM configuration (confirm your exact calibration)
Can I drive?	Usually yes for a short distance, but fix it soon. Warning faults like MID 128 PID 81 FMI 2 commonly escalate into torque derate if ignored. The scan-tool checks below help determine urgency.

Symptoms

Likely causes

Fixes

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What does MID 128 PID 81 FMI 2 mean?

When MID 128 PID 81 FMI 2 sets, the ECM is indicating a fault condition that affects performance, protection strategy, or emissions (depending on calibration).

OEM definitions can vary slightly, so confirm your exact meaning with your service manual or diagnostic tool.

Treat repeat faults as ACTIVE and diagnose using a scan tool and basic inspections before replacing parts.

How this system works (why MID 128 PID 81 FMI 2 happens)

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

A single event might store a code, but repeated events across drive cycles are what typically trigger warnings, derate strategies, or inducement (emissions systems).

Your goal is to identify the failure mode (electrical, mechanical, sensor drift, or upstream cause) rather than “parts cannon” replacement.

Detailed guide for MID 128 PID 81 FMI 2

MID 128 PID 81 FMI 2 - Particulate Filter

**Fault Type:** Data erratic, intermittent or incorrect

Fault Condition

Sensor is not rational (output is erratic or implausible)

Possible Symptoms

Malfunction indicator lamp illuminated

Possible Causes

Particulate Trap Pressure (PTP) Sensor failure
Loose or corroded connections
Intermittent wiring issue

Diagnostic Tips

1. Check sensor connector for corrosion or damage

2. Inspect wiring harness for intermittent shorts or opens

3. Monitor sensor signal with diagnostic tool while gently moving wiring

4. Check for water intrusion in sensor connector

5. Verify pressure tubing is not partially blocked or leaking

Location hint for MID 128 PID 81 FMI 2

The DPF differential pressure sensor is usually mounted on/near the firewall or aftertreatment bracket. It connects to the exhaust via two small pressure tubes (pre- and post-DPF). Check the tubes for soot blockage, cracks, water intrusion, and heat damage.

Tip: Soot blockage or water in the DP tubes is a very common cause of erratic differential pressure readings.

Scan tool checks for MID 128 PID 81 FMI 2

Check status: ACTIVE vs INACTIVE / stored. If it’s not active, review last occurrence conditions (freeze-frame if available).
Record companion codes (regen inhibited, soot load, exhaust leak, sensor supply voltage). Fix upstream causes first.
Inspect DP sensor tubes/hoses for soot blockage, cracks, melted sections, and water intrusion.
Compare DP readings at idle vs under load. Erratic signals often point to wiring, sensor, or blocked tubes.

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 81 FMI 2

Visual inspection (fast wins). Sensor connector/wiring, DP sensor tubes/hoses, soot blockage, water intrusion, exhaust leaks.
Check fluid sanity. Not applicable unless your fault is fluid-related. Focus on inspections + repeatability.
Confirm the fault is ACTIVE. Stored-only faults can be old events.
Run actuator tests (if supported). Use OEM diagnostic software (examples: Cummins INSITE, Detroit DDDL, PACCAR DAVIE4) (or a capable J1939 tool) to command tests when available.
Verify after repair. Clear codes, road test, confirm it stays inactive.

Decision guide (fast path) for MID 128 PID 81 FMI 2

If the fault is STORED only → inspect DP tubes/hoses + wiring, clear, and monitor. If it returns, treat it as active.
If ACTIVE → check tubes for blockage/water → then verify wiring/connector → then evaluate sensor readings plausibility.
If exhaust leak codes exist → fix leaks first. Leaks can skew delta-P readings.

Common misdiagnosis mistakes for MID 128 PID 81 FMI 2

Replacing sensors without checking wiring, grounds, and connector pin fitment.
Clearing codes repeatedly without confirming whether the fault is ACTIVE and repeatable.
Missing companion codes that point to the real upstream problem.

Will MID 128 PID 81 FMI 2 cause derate or inducement?

Warning aftertreatment faults often start as an emissions warning, then progress to torque derate if the fault remains active over multiple drive cycles. If ignored, many platforms can eventually enter inducement and severe speed limiting.

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

“Do this first” checklist for MID 128 PID 81 FMI 2

Scan for companion codes (regen inhibited, soot load, exhaust leak, sensor supply voltage).
Inspect DP sensor tubes/hoses for soot blockage, cracks, melted spots, and water intrusion.
Check wiring/connector pin fitment at the DP sensor (chafing and loose pins are common).
Verify exhaust system integrity (leaks before/after DPF can skew delta-P readings).
Clear codes and perform a controlled drive/regen to confirm readings are stable.

Tools needed to diagnose MID 128 PID 81 FMI 2

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 actuator tests and live data

Prevention tips to avoid repeat MID 128 PID 81 FMI 2

Inspect DP sensor tubes/hoses during service. Soot blockage builds over time.
Fix exhaust leaks early. They can skew DP readings and regen behavior.
Avoid excessive idling when possible (regen systems hate it).
Watch for water intrusion in sensor lines after heavy rain/steam cleaning.

What to check first for MID 128 PID 81 FMI 2

Inspect connectors and harness near the affected component for corrosion, rubbing, or loose pins.
Inspect DP sensor tubes/hoses for blockage, water, or heat damage.
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. Many faults escalate into derate when ignored.

Related fault codes

No related faults found yet. Commonly seen with: SPN 5246, SPN 1569, SPN 4364, SPN 3719.

Mechanic community notes for MID 128 PID 81 FMI 2

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