Technical Guides

Fault Codes & Repair, FMI 7, Mack, SPN 641, Turbo actuator, VGT, Volvo

SPN 641 FMI 7: Turbocharger Actuator Not Responding — Diagnostic Guide

Learn how to diagnose SPN 641 FMI 7 without replacing the turbo first: actuator power, linkage, VGT movement, wiring and calibration checks.

Motorsymph Diesel Technical Team | August 21, 2026

Aftertreatment, DPF, Fault Codes & Repair, FMI 0, Forced regeneration, Soot load, SPN 3719

SPN 3719 FMI 0: DPF Soot Level Very High — Safe Diagnostic Guide

SPN 3719 FMI 0 indicates a critically high DPF soot level on many platforms. Learn when a regen may be unsafe and what to diagnose first.

Motorsymph Diesel Technical Team | August 21, 2026

Boost pressure, Fault Codes & Repair, FMI 18, Intake manifold pressure, SPN 102, Turbocharger

SPN 102 FMI 18: Intake Manifold Pressure Too Low — Diagnostic Guide

Diagnose SPN 102 FMI 18 methodically: intake and charge-air leaks, restrictions, sensor plausibility, turbo control and OEM verification.

Motorsymph Diesel Technical Team | August 21, 2026

Aftertreatment, DEF, Fault Codes & Repair, FMI 18, NOx sensor, SCR, SPN 4364

SPN 4364 FMI 18: SCR NOx Conversion Efficiency Low — Diagnostic Guide

Learn what SPN 4364 FMI 18 means, the most common SCR and DEF causes, and the correct diagnostic order before replacing a NOx sensor.

Motorsymph Diesel Technical Team | August 21, 2026

Cummins, Fault Codes & Repair, FMI, SPN, Truck Diagnostics

Cummins Fault Code List: SPN & FMI Codes Explained (2026 Guide)

A technician's Cummins fault code list: how SPN and FMI work together, a reference table of the most common Cummins engine and aftertreatment codes, and how to read and clear...

Motorsymph Diesel Technical Team | August 20, 2026

CAT ET, Caterpillar, Fault Codes & Repair, Off-Highway Diagnostics

Caterpillar Fault Codes List: MID, CID & FMI Explained (2026)

A technician's Caterpillar fault code list: what MID, CID and FMI mean, how CAT codes differ from J1939, the difference between fault codes and event codes, and how to read...

Motorsymph Diesel Technical Team | August 20, 2026

DPF, Fault Codes & Repair, Regeneration, Truck Diagnostics

How Long Does a DPF Regen Take? Parked, Active & Forced Regen Explained

How long a DPF regen takes (passive, active and parked/forced), what the regen light means, why regens fail to complete, and how to run a forced regeneration with diagnostic software.

Motorsymph Diesel Technical Team | August 20, 2026

Caterpillar MID CID and FMI fault-code troubleshooting

Fault Codes & Repair, Off-Highway Diagnostics

How to Read Caterpillar Fault Codes: MID, CID and FMI Explained

How to read Caterpillar fault codes: what MID, CID and FMI mean, how to decode a CAT code, the difference between fault codes and event codes, severity levels, and how...