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Heavy-Duty Diesel Truck Fault Codes

Decode fault codes from Class 7 and Class 8 on-highway trucks. Covers Cummins ISX and X15, Detroit Diesel DD13 / DD15 / DD16, PACCAR MX-11 and MX-13, CAT C15 ACERT, Volvo D13, Mack MP8, MaxxForce, Hino, and Isuzu. Includes J1939 SPN/FMI pair decoding, regen / derate conditions, aftertreatment faults, and common shop fixes.

1092 heavy-duty fault codes documented · across 9 engine families

Most Common Heavy-Duty Fault Codes

Showing 30 of 1092 heavy-duty diesel codes (sorted by severity). Each links to causes, diagnostics, common fixes, and repair cost estimates.

CAT-CID100-FMI3 critical
Engine Oil Pressure Sensor - Voltage Above Normal (Open/Short to High)
CAT-CID100-FMI4 critical
Engine Oil Pressure Sensor - Voltage Below Normal (Short to Low)
CAT-SKIDSTEER-100-1 critical
Engine Oil Pressure Below Safe Operating Threshold
CAT-SKIDSTEER-110-0 critical
Engine Coolant Temperature High Shutdown
CAT-SKIDSTEER-190-0 critical
Engine Overspeed Shutdown, ECM Cut Fuel
CAT-SKIDSTEER-5246-15 critical
Aftertreatment Inducement Severe Derate Active
CAT-SPN100-FMI1 critical
Engine Oil Pressure Low
CAT-SPN110-FMI0 critical
Engine Coolant Temperature Above Normal
CAT-SPN111-FMI1 critical
Coolant Level Low
CAT-TH-100-1 critical
Engine Oil Pressure Below Safe Operating Threshold
CAT-TH-110-0 critical
Engine Coolant Temperature High Shutdown Fault
CAT-TH-190-0 critical
Engine Overspeed Shutdown: RPM Exceeded Safe Limit
CAT-TH-5246-15 critical
EPA Aftertreatment Inducement Derate Active
CUMMINS-111 critical
ECM Critical Internal Failure
CUMMINS-115 critical
Engine Magnetic Speed/Position Lost Both of Two Signals
CUMMINS-143 critical
Oil Pressure Low - Warning
CUMMINS-151 critical
Engine Coolant Temperature High - Critical
CUMMINS-1663 critical
Aftertreatment 1 Diesel Oxidation Catalyst Missing
CUMMINS-1664 critical
Aftertreatment 1 Diesel Particulate Filter Missing
CUMMINS-1679 critical
Aftertreatment SCR Operator Inducement Severity
CUMMINS-217 critical
Engine Coolant Temperature High - Shutdown
CUMMINS-218 critical
Intake Manifold Temperature High - Shutdown
CUMMINS-219 critical
Engine Oil Pressure Extremely Low - Shutdown
CUMMINS-234 critical
Engine Crankshaft Speed/Position - Data Erratic (High)
CUMMINS-235 critical
Coolant Level Low - Critical
CUMMINS-254 critical
Fuel Shutoff Valve - Current Below Normal
CUMMINS-255 critical
Fuel Shutoff Valve - Current Above Normal
CUMMINS-259 critical
Fuel Shutoff Valve Stuck Open
CUMMINS-2641 critical
Aftertreatment SCR System - Fault Severity 1
CUMMINS-2642 critical
Aftertreatment SCR System - Fault Severity 2
Browse all 1092+ heavy-duty codes →

Browse by Engine

Cummins ISX / X15 / ISB 6.7L

Cummins ISX, X15, ISB 6.7L, ISL, ISC, and ISM. Big bore on-highway and medium-duty pickup. SPN/FMI pairs, regen issues, derate conditions.

PACCAR MX-11 / MX-13

PACCAR MX-11 and MX-13 fault codes in Kenworth and Peterbilt trucks. ECM, aftertreatment, EGR, and turbo faults.

Detroit Diesel DD13 / DD15 / DD16

Detroit Diesel DD-series fault codes for Freightliner Cascadia and Western Star. J1939 SPN/FMI + ACM codes.

Caterpillar C7 / C9 / C13 / C15

Pre-2010 CAT on-highway diesel engines: C15 ACERT, C13 ACERT, C9, C7. CID/FMI codes via CAT ET, EGR cooler failures, HEUI faults.

MaxxForce DT / 7 / 11 / 13

International MaxxForce engines (Navistar). DT medium-duty workhorse, MaxxForce 11/13 EGR-only emissions strategy that triggered massive recalls.

Volvo D11 / D13 / D16, Mack MP7 / MP8 / MP10

Volvo & Mack share architecture (Volvo Group). EGR cooler, DEF dosing, NOx sensor faults via Volvo Tech Tool / PTT.

Hino J05E / J08E / A05 / A09

Toyota Group medium-duty: 195, 268, 268A, 338, 358, M5, L6, L7, XL7, XL8. DPF regen, DEF / SCR dosing diagnostics via Hino DX.

Isuzu 4HK1-TC / 6HK1

NPR / NPR-HD / NPR-XD / NQR / FTR / FVR / FRR cab-over delivery trucks. DPF, DEF, EGR, and common-rail diagnostics via Isuzu IDSS.

What is a Heavy-Duty Diagnostic Code?

Heavy-duty trucks communicate over the J1939 CAN bus, a protocol defined by SAE for commercial vehicles. Unlike light-duty OBD-II (which uses P/B/C/U codes), J1939 faults are reported as SPN (Suspect Parameter Number) paired with an FMI (Failure Mode Identifier). For example, SPN 3251 FMI 0 describes a DPF outlet pressure above normal operating range. Some manufacturers also emit proprietary "fault codes" (Cummins FC 3712) or flash codes in addition to J1939 SPN/FMI pairs.

Common Heavy-Duty Fault Categories

  • Aftertreatment (DPF, DEF, SCR, dosing unit, NOx sensors)
  • EGR system (cooler, valve, differential pressure)
  • Turbocharger (VGT actuator, boost pressure, overspeed)
  • High-pressure fuel system (rail pressure, injectors, CP pump)
  • Engine derate conditions (inducement levels 1-4)
  • Air system (charge air cooler leaks, intake manifold pressure)
  • Transmission (Allison 3000/4000, Eaton Fuller UltraShift, ZF TraXon)

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