AftertreatmentCaterpillar Diesel ECM

SPN 3361 / SPN 3821

Name: ECM Performance
Address: Fort Lauderdale, FL, 33325, US
Telephone: (888) 768-2447
Price range: $$-$$$

DPF, DEF, SCR, and NOx-reduction system faults.

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System

Caterpillar Aftertreatment

Caterpillar ECM Service

Diagnostic Overview

CAT codes listed as 3361/3821 commonly belong to the DEF dosing or SCR control side of the aftertreatment system. The ECM may be detecting that commanded DEF delivery, DEF pressure, or SCR response does not match expected operation. In practical terms, the machine may continue to run but can set warnings or inducement levels if the issue remains active. The exact diagnostic direction depends on the FMI, so the first step is always to read the complete code in Cat ET.

Likely Causes

Restricted DEF filter; crystallized doser; weak DEF pump; frozen or contaminated DEF; wiring damage; failed DEF pressure or quality sensor; SCR dosing control fault.

What To Check First

Confirm the complete SPN/FMI, check DEF quality, inspect the DEF doser for crystallization, verify pump pressure, and review SCR efficiency or NOx-related codes.

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Related Aftertreatment Fault Codes

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SPN 1761 FMI 17

CAT fault code 1761-17 commonly relates to diesel exhaust fluid level or a DEF level signal that is below the expected range.

SPN 3360 / SPN 3820

CAT codes listed as 3360/3820 generally point toward the DEF supply, DEF quality, DEF tank, or SCR dosing system depending on the exact FMI shown in Cat ET.

SPN 3474 FMI 31

CAT fault code 3474-31 is typically associated with aftertreatment regeneration or ARD-related operation.

SPN 3701 FMI 15

CAT fault code 3701-15 commonly indicates an aftertreatment condition that is above normal but at a least-severe level, often connected with DPF soot load, regeneration need, or aftertreatment restriction.

SPN 3701 FMI 16

CAT fault code 3701-16 usually represents a more serious aftertreatment condition than 3701-15, with the measured or calculated value above normal at a moderate severity level.

SPN 3719 FMI 0

CAT fault code 3719-0 is generally an aftertreatment soot-load or DPF restriction code at a high-severity level.

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