Fault 3474-31 on Claas Lexion 750 740 - ARD head ignition problem

Fault code 3474-31, often found on Claas Lexion 750s, indicates a malfunction of the ARD head, responsible for disturbances in the regeneration process. This type of fault, directly linked to the anti-pollution devices, leads to engine cut-offs, a degraded mode, or even a complete shutdown. To remedy this, advanced reprogramming of the Adem 4 ECU deactivates the ARD and associated components (AdBlue, DPF), ensuring reliable, uninterrupted operation. As a result, the CAT C9.3 engine returns to optimal operation, adapted to real-life conditions.

Defects 3474-31 and 3719-16 on Claas Lexion 750: Related defects and problems

Fault 3474-31, also referenced as SPN 3474 FMI 31, signals an interruption in the DPF regeneration process on Claas Lexion combines, notably models 740, 750 and 760. This code appears when the Caterpillar C9.3 engine, equipped with the Adem 4 ECU, detects a loss of combustion in the ARD head. Regeneration starts, but combustion stops prematurely, preventing soot removal and forcing the engine to limit power.

Fault 3474-31 is triggered when the Adem 4 ECU detects a loss of effective combustion in the ARD head while DPF regeneration is in progress. This problem can be caused by a number of mechanical, electronic or engine management components. Here are the most frequent causes observed in the field:

3719-16 - High soot content in DPF (moderate severity)

Exact translation : "DPF #1 Soot Loading Percent: High - moderate severity (2)"

Fault code 3719-16 signals excessive soot accumulation in the particulate filter (DPF). This alert is triggered when the soot load level calculated by the Adem 4 ECU exceeds a critical threshold defined in the engine calibration. The system then considers that conditions are no longer acceptable for normal operation.

This code is associated with severity level 2, triggering an automatic reduction in engine torque. The degraded mode is activated to protect the engine and exhaust system from overheating or complete clogging of the DPF.

In the vast majority of cases, this code occurs just after a failed regeneration attempt, such as the one generated by fault 3474-31(Aftertreatment Failed to Ignite). In other words, the system has attempted to burn off the soot, but since combustion has not started or has stopped, the soot remains stored and continues to accumulate.

🔌 Internal heater defective (ARD Heater)

The heating resistor built into the ARD head ensures that a sufficient temperature is reached to initiate fuel combustion. If this resistor is partially cut, short-circuited, or has an abnormal ohmic resistance, the head will not reach the required temperature. The system then remains in cold combustion or fails to maintain a stable flame. When tested via CAT ET, the current consumption should reach 5.5 to 6 A. A lower value indicates a heater module failure.

💧 Insufficient ARD fuel pressure common with Fault 3474-31 on Claas Lexion 750

The ARD head features a special injector, fed by a bypass in the fuel circuit. If the supply pressure is too low, due to a clogged filter, faulty auxiliary pump or leak, injection becomes insufficient to maintain stable combustion. Even if initial ignition occurs, the flame may go out for lack of fuel, triggering fault 3474-31.

🌡️ Temperature sensors faulty

Sensors located at the inlet and outlet of the ARD head monitor the temperature rise. If one of these sensors returns an inconsistent value or remains frozen, the ECU considers that combustion has not started, even if it has physically taken place. This is a typical case of a "phantom" fault, reflecting not a mechanical failure but an erroneous sensor feedback.

🧪 ARD injector clogged or out of sync

The ARD fuel injector can become clogged with impurities, particularly if the associated filter is neglected or if the circuit is not regularly bled. In some cases, out-of-sync ECM control (incorrect opening timing) prevents fuel from being injected at the right moment in relation to the heating phase, making ignition impossible.

🧱 DPF clogging and excessive backpressure

A partially or totally blocked DPF creates excessive upstream back pressure. This pressure prevents the gases from flowing properly through the ARD head, disrupting combustion and making it unstable. The system may trigger a regeneration attempt, but the internal dynamic conditions do not allow stable operation, so the procedure is interrupted.

🧯 Overheating, soot, and fire hazard on Claas Lexion

If fault 3474-31 is not dealt with quickly, the DPF overheats, and the temperature in the exhaust system rises dangerously. This overheating can cause major thermal damage.

On the Claas Lexion 740, 750 and 760, several cases of fire outbreaks have been reported. Excessive heat causes the nearby diesel fuel tank to melt, igniting the fuel. This scenario represents a real risk, especially at harvest time, when conditions are hot and dusty.

How to find a permanent solution

🧠 Steps in the removal process via reprogramming

1. 📥 ECU connection with CAT ET

First connect the CAT Comm Adapter III interface to the machine's diagnostic port, then launch the CAT ET (Electronic Technician) software. The tool provides access to real-time parameters, fault histories, sensor values and the current configuration of the Adem 4 ECU.

2. 📋 Save current configuration

Prior to any modification, a complete reading of the ECM parameters is performed. Some tools allow you to extract the calibration file (flash file .fls) associated with the model and serial number. This step is crucial if you wish to return to the original settings (factory backup).

3. 🔧 Read calibration file

Data is extracted from the ECU via a reading tool such as Kess, New Genius, BDM, KTAG, or Bench (depending on protocol and support). On Adem 4, this is often done via BDM or Boot Mode, as some models are OBD protected.

The extracted file contains not only the engine mapping, but also the SCR, DPF, EGR and ARD management modules. This is where we come in.

4. 🧱 Suppression of anti-pollution functions

In the .bin or .fls file, modify :

• ARD block → deactivation of afterburner injection and heater

• Automatic regeneration management → DPF trip neutralization

• Soot rate calculation → replacement by a low constant value

• Torque Derate strategy → remove condition 3719-16

• DTC codes → Aftertreatment error disabling (3474, 357, 3719, etc.)

This step must be carried out with care, keeping all other functional blocks (temperature, pressure, motor safety) intact.

5. 💾 Rewriting in ECM

Once the calibration has been modified, the Adem 4 ECU is re-flashed with the corrected file. Use either CAT ET (with a modified flash file), or a Trasdata / KTAG / Bench tool to inject directly in Boot mode.

6. ✅ Validation of intervention

Once the ECU has been reprogrammed :

• Fault codes are missing

• Regeneration no longer restarts

• Motor runs without torque reduction

• ARD system electrically disconnected, without generating an alert

The ECM continues to manage essential engine functions, without triggering anti-pollution strategies or generating DPF or soot alerts.