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Cummins MID 128 PID 102 FMI 3: Meaning, Causes & Fix

Boost Pressure Sensor — signal voltage above normal or shorted high

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Diagnostic Reference

Field Details
Code MID 128 PID 102 FMI 3
Protocol J1587 MID: 128 PID: 102
Component Intake Manifold Pressure Sensor
Manufacturer Cummins
Engine Series ISX15
Severity 🟠 CHECK SOON
SAE Reference SAE J1587/J1708 — MID 128, PID 102

Possible Causes

  1. Shorted-to-voltage in signal wire
  2. Faulty MAP sensor
  3. ECM 5V reference overload
  4. Corroded connector pins

Diagnostic & Repair Procedure

  1. Step 1: Backprobe signal wire at sensor connector for 5V reference
  2. Step 2: Replace MAP sensor if reference voltage is correct
  3. Step 3: Inspect ECM connector for moisture ingress
  4. Step 4: Clear codes and road-test

Frequently Asked Questions

Is this a false alarm or a real problem?

CHECK SOON codes are rarely false alarms. The ECM has detected a parameter outside normal operating range. Sensor malfunctions can sometimes trigger false readings, but the majority of CHECK SOON codes indicate a developing issue that will worsen if left unaddressed. Use a diagnostic scan tool to verify sensor readings before replacing expensive parts.

Can I diagnose this without a scan tool?

Basic visual inspection can be performed without a scan tool — check wiring harnesses for chafing, connectors for corrosion, and related components for physical damage. However, to verify the fault, view live sensor data, and confirm the repair, a heavy-duty diagnostic scan tool (or a compatible OBD-II adapter with J1939/J1708 support) is strongly recommended for accurate diagnosis.

How soon should I schedule service?

Schedule service within the next 1–3 operating days. While the vehicle can continue operating normally, delaying repair increases the risk of the fault escalating to CHECK NEXT STOP severity. Additionally, some CHECK SOON conditions are precursors to emissions system faults that will trigger a mandatory derate if not addressed in a timely manner.

Diesel Repair Cost & Downtime Estimator

Enter estimated labor hours to calculate repair cost and potential fleet downtime losses. Based on national average diesel shop rate of $150/hr and daily revenue loss of $800/day for a parked truck.

Related Fault Codes — ISX15

SPN 1569 FMI 31 🔴 STOP ENGINE
Engine Protection Torque Derate
SPN 102 FMI 18 🔴 STOP ENGINE
Intake Manifold Pressure critically low
SPN 111 FMI 18 🔴 STOP ENGINE
Engine Coolant Level critically low
SPN 639 FMI 9 🔴 STOP ENGINE
J1939 CAN Bus Communication Loss
SPN 1322 FMI 31 🟡 CHECK AT NEXT STOP
Misfire Detected on Cylinder 6
MID 128 SID 1 FMI 5 🟡 CHECK AT NEXT STOP
Injector Cylinder 1 Circuit

Associated Symptoms

Check Engine Light Erratic Boost Gauge Engine Derate

References & Further Reading

Data Provenance: This fault code definition is derived from SAE J1587 standards. MID 128 PID 102 as defined in SAE J1587/J1708. Diagnostic procedures sourced from Cummins OEM technical service documentation. Not for safety-critical decisions. Consult a certified diesel mechanic before performing any repair. See our full disclaimer.