Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température: Pourquoi ces 7 Les pièces critiques sont essentielles au contrôle des émissions

Bienvenue dans ce guide technique critique sur le Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température (Assemblée 551). This is the complete set of electronic “les yeux et les oreilles” for the emissions after-treatment system on the FAW Jiefang CA4251P66K24T1A3E5 6×4 tracteur semi-remorque diesel.

Le Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température est le “logique” hub for the truck’s Selective Catalytic Reduction (SCR) système. Its components, the ‘Nitrogen-oxygen sensor assembly’ (3602510-51B) and the ‘High-temperature sensor assembly’ (3602505-51B-C00), provide the real-time data that the engine’s computer (ECU) needs to precisely manage the injection of Diesel Exhaust Fluid (DEF/Urea) and control emissions.

Ce guide détaillé est une ressource essentielle pour les techniciens professionnels diesel et les spécialistes des pièces détachées.. Nous déconstruirons l'ensemble Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température dans son 7 composants réparables, expliquant la critique “logique” of each sensor, their function in the SCR system, and the mounting brackets that protect them.

Le “Logique” of SCR: How This Assembly Works

Le Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température est le “cerveau” of the modern emissions system. This system is known as **Selective Catalytic Reduction (SCR)**. Its sole purpose is to convert harmful Nitrogen Oxides (NOx)—a major component of smog and acid rain—into harmless nitrogen (N2) et de l'eau (H2O).

This chemical reaction is achieved by injecting Diesel Exhaust Fluid (DEF), a solution of urea and water, into the hot exhaust stream just before it enters a special catalyst (the SCR catalyst, part of Assembly 127).

This is where the “logique” de la Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température comes in. The truck’s Engine Control Unit (ECU) must know the *exact* amount of DEF to inject.

• **Inject Too Little:** If the ECU injects too little DEF, the chemical reaction will be incomplete. Harmful NOx will pass through the catalyst untreated, causing the truck to fail emissions standards and trigger a “Vérifier le moteur” light or “Limp Mode.”
• **Inject Too Much:** If the ECU injects too much DEF, it wastes expensive fluid and, more critically, causes “ammonia slip.” The excess urea doesn’t react and can crystallize (“cake”) inside the exhaust, creating a massive, concrete-like blockage that can destroy the SCR catalyst and even damage the engine.

Le Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température fournit le “en boucle fermée” feedback the ECU needs to inject the perfect, stoichiometric amount of DEF. It is the sensory input that makes this precise chemical reaction possible.

Composant principal 1: ‘Nitrogen-Oxygen Sensor Assembly’ (3602510-51B)

The ‘Nitrogen-oxygen sensor assembly’ (3602510-51B) is the most complex and critical part of the Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température. This is not a simple sensor; c'est un sophistiqué, multi-cell ceramic device with its own integrated control module.

**Fonction:** This sensor is typically installed *after* the SCR catalyst. C'est “logique” est d'être le “report card” for the entire after-treatment system. It precisely measures the remaining parts-per-million (PPM) of Nitrogen Oxides (NOx) in the exhaust gas *after* it has been treated.

This sensor provides the final “feedback” in the closed-loop system. The ECU constantly monitors this sensor’s readings. If it detects that NOx levels are starting to creep up, il “sait” that its current DEF injection rate is insufficient, and it will precisely increase the injection “garniture” until the sensor reports that NOx levels are back to near-zero.

**Échec:** The NOx sensor is a high-wear component in the Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température. It lives in an extremely hot, high-vibration environment and is sensitive to contamination from poor-quality fuel or DEF. A failed NOx sensor is a critical fault. The ECU loses its “yeux,” can no longer verify the emissions, and will immediately trigger a “Vérifier le moteur” lumière, un “Limp Mode” (severe engine power reduction), and will log a fault for the emissions-control system. Le Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température is completely disabled without this sensor.

Composant principal 2: ‘High-Temperature Sensor Assembly’ (3602505-51B-C00)

The ‘High-temperature sensor assembly’ (3602505-51B-C00) is the second “logique” composante du Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température. This is a high-grade thermistor or thermocouple designed to withstand extreme exhaust temperatures (over 800°C).

**Fonction (SCR Logic):** The chemical reaction of DEF (urée) converting NOx is highly temperature-dependent. It only works efficiently within a specific temperature “fenêtre” (Par exemple, 200°C to 450°C). Le “logique” of this sensor is to tell the ECU when it is safe to start injecting DEF. If the ECU injects DEF into a “froid” (below 200°C) système d'échappement, the urea will not convert to ammonia; it will simply crystallize, forming hard, white deposits (“caking”) that will block the SCR catalyst, a catastrophic and expensive failure. This sensor in the Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température prevents that.

**Fonction (DPF Logic):** This sensor also provides the critical “logique” for **DPF Regeneration**. The Diesel Particulate Filter (FAP) traps soot, and it must be periodically cleaned out by “regenerating” (burning the soot at over 600°C). The ECU relies on this sensor to monitor the DPF’s temperature, assurer un “regen” is both successful and safe (C'est-à-dire, it doesn’t get hot enough to melt the catalyst). This is a dual-purpose, essential component of the Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température.

Le système de montage et de support

The delicate electronic sensors in the Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température cannot simply be left to hang. They must be rigidly secured and their wiring protected from melting or chafing.

**’Nitrogen-oxygen sensor upper bracket’ (3602546-81W):** Ce support est “logique” est une protection. The NOx sensor (3602510-51B) is a two-part device: le “probe” that screws into the exhaust pipe, et un “control module” (a small black box) connected by a wire. This bracket is designed to mount the *control module* safely on the chassis frame, away from the extreme heat of the exhaust.

**’Main wiring harness bracket’ (3724426-68V):** This bracket is used to secure the main wiring harness for the Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température, preventing the wires from rubbing against the chassis (which would cause a short) or dangling near the hot exhaust pipe (which would melt them).

These brackets are secured with ‘Hex flange bolts’ (Q1840616) et « Écrous à bride hexagonale’ (CQ39606). Le “bride” design is a vibration-resistant logic that prevents the fasteners from loosening. Enfin, the two ‘Plastic zip ties’ (T67417246) are a simple but critical part of the Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température, used to provide the final, secure fastening for the sensor wires.

FAW Nitrogen-Oxygen Sensor And High-Temperature Sensor Logic Assembly Parts List

Le tableau suivant fournit l'intégralité, ventilation détaillée de tous 7 components identified in the ‘Nitrogen-Oxygen Sensor And High-Temperature Sensor Logic Assembly’ (551) schéma du tracteur FAW CA4251P66K24T1A3E5.

Spécifications techniques et contexte d'assemblage

Les spécifications pour le Capteur d'azote-oxygène FAW et ensemble logique de capteur haute température sont définis par sa fonction de “cerveau” of the emissions after-treatment system.