Cat® C9.3–C18 ACERT™ Fault Codes Guide – Diagnostic & Event Code Reference

Cat® C9.3 ACERT™ Through C18 ACERT Fault Codes Guide

Learn how Cat® C9.3 ACERT™ through C18 ACERT engines report issues using diagnostic codes, event codes, and severity levels, and how to retrieve these codes using Cat ET or flash codes.

 Understanding how Cat® C9.3 ACERT™ through C18 ACERT engines communicate issues is vital. The engine management system uses two types of numerical codes to alert technicians to problems: Diagnostic Codes and Event Codes.

1. Categorizing the Codes

Diagnostic Codes

Diagnostic Codes are triggered by a malfunction in the electronics, such as a sensor, circuit, or ECU failing or entering a fault condition. These codes point directly to issues in the electronic or control system.

Event Codes

Event Codes are raised when electronic components measure a physical value (like temperature or pressure) that is outside of a pre-configured, safe operating threshold. These codes indicate that the engine is operating outside its intended limits.

2. Understanding Severity Levels

Every code is assigned a severity level that dictates how the engine and monitoring system respond:

Level 1 (Least Severe)

Warning only. No immediate action is required, but the system will likely need attention soon.

Level 2 (Moderate Severity)

Engine Derate. The ECU will reduce engine power by a specific percentage to protect components while allowing continued (though limited) operation.

Level 3 (Most Severe)

Shutdown. The system activates or advises an immediate safe shutdown to prevent catastrophic damage.

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3. How to Retrieve Codes

Technicians have two primary ways to access these codes:

Cat ET (Electronic Technician)

Cat ET is the most comprehensive method. It displays the full J1939 fault code, including the Suspect Parameter Number (SPN), Failure Mode Indicator (FMI), and occurrence count.

Flash Codes

If a service tool isn't available, you can cycle the keyswitch from "Off" to "On" twice within three seconds. The diagnostic lamp will then flash the codes in sequence.

For example, code 133 would be:

• One flash
• A pause
• Three flashes
• A pause
• Three more flashes

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4. Common Error Codes Reference

Here are some of the critical codes and their associated triggers identified in the sources:

Cooling System

System	J1939 SPN-FMI	Description	Engine Action
Coolant	110-15 (E361-1)	High Engine Coolant Temp (L1)	Warning Lamp
	110-16 (E361-2)	High Engine Coolant Temp (L2)	Derate
	110-00 (E361-3)	High Engine Coolant Temp (L3)	Shutdown

Oil Pressure

System	J1939 SPN-FMI	Description	Engine Action
Oil Pressure	100-17 (E360-1)	Low Engine Oil Pressure (L1)	Warning Lamp
	100-01 (E360-3)	Low Engine Oil Pressure (L3)	Shutdown

Aftertreatment

System	J1939 SPN-FMI	Description	Engine Action
Aftertreatment	3719-16	100% Soot Loading	Warning (Amber) Flash
	3715-31	140% Soot Loading	Shutdown
	3720-15	5000 Hour Ash Loading (L1)	Logged Event
	3720-16	5100 Hour Ash Loading (L2)	Warning Lamp

Regen System

Regen System Code:

• 3474-14 — HSR Regen Flameout → Inhibits HSR

Throttle

Throttle / Switch Codes:

• 29-2 or 774-2 — Invalid MPTS Switch Combo → ECU ignores switch

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5. Emissions and Tampering Codes

The emissions system has specific protections. The Engine Emissions System Failure Lamp is triggered by two main categories: Tampering and DEF level faults.

The system will detect tampering—such as an unplugged NOx sensor or DEF injector—within one hour of the event. If a DEF tank level sensor is disconnected while the pump loses prime, final inducement (shutdown or idle-only) is imposed immediately.

FAQs: Cat® ACERT™ Engine Fault Codes

Q1: What is the difference between Diagnostic Codes and Event Codes on Cat ACERT engines?

Diagnostic Codes are triggered by malfunctions in the electronics, such as sensors, circuits, or the ECU. Event Codes are raised when physical values like temperature or pressure move outside of safe operating thresholds. Both are essential for understanding engine health, but they point to different types of problems.

Q2: What do the severity levels (L1, L2, L3) mean?

Level 1 is the least severe and results in a warning only. Level 2 is moderate severity and causes an engine derate to protect components. Level 3 is the most severe and triggers or advises an immediate shutdown to prevent catastrophic engine damage.

Q3: How can I retrieve codes without Cat ET?

You can use flash codes by cycling the keyswitch from "Off" to "On" twice within three seconds. The diagnostic lamp will flash the codes in sequence. For example, code 133 would be one flash, a pause, three flashes, a pause, and three more flashes.

Q4: What happens if the DEF level sensor or NOx sensor is unplugged?

The system detects tampering, such as an unplugged NOx sensor or DEF injector, within one hour. If the DEF tank level sensor is disconnected while the pump loses prime, final inducement is imposed immediately, which can mean shutdown or idle-only operation to protect the emissions system.