FAW Rear Axle Sensor Logic Assembly: A Critical Analysis of 4 Core ABS/TCS Components

Welcome to this critical technical guide on the FAW Rear Axle Sensor Logic Assembly (Assembly 555). This is the complete, high-precision “wheel speed sensing” system for the rear *drive axles* of the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor. This assembly is the primary “eyes and ears” for the vehicle’s Anti-lock Braking System (ABS) and Traction Control System (TCS).

The FAW Rear Axle Sensor Logic Assembly is a set of components with one vital “logic” function: to precisely measure the rotational speed of each rear drive wheel and report it, in real-time, to the truck’s main ECU and ABS computer. This data is the foundation of all modern active safety systems on the 6×4 tractor.

This in-depth guide is an essential resource for professional diesel technicians and parts specialists. We will deconstruct the entire FAW Rear Axle Sensor Logic Assembly into its 4 core serviceable components: the ‘Wheel speed sensor’ (3605360-A6T-S), the ‘Sensor bracket’ (3550117A377-S), the ‘Sensor sleeve’ (3550361-6S), and the ‘Wire guide bushing’ (3605221-A6T-S). A failure in this FAW Rear Axle Sensor Logic Assembly can compromise the truck’s safety and braking performance.

The “Logic” of ABS and Traction Control (TCS)

The FAW Rear Axle Sensor Logic Assembly is the sensory input for the truck’s most critical active safety systems. Its “logic” is not mechanical, but electronic. It answers one question, hundreds of times per second: “How fast is this wheel turning?” This data is essential for both the Anti-lock Braking System (ABS) and the Traction Control System (TCS).

**Anti-lock Braking (ABS) Logic:** When a driver performs a “panic stop” on a wet or icy road, the immense force from the brake chambers can “lock” the drive wheels. A locked wheel has zero traction and can cause a dangerous “jackknife” situation. The FAW Rear Axle Sensor Logic Assembly prevents this. The moment a sensor (3605360-A6T-S) reports a wheel speed of “zero” (a lock-up), the ABS computer instantly commands the brake solenoid (see Assembly 539/545) to release and re-apply the brake on that specific wheel, “pumping” it far faster than any human. This “anti-lock” logic keeps the wheel *just* on the verge of locking, providing maximum stopping power while maintaining stability.

**Traction Control (TCS) Logic:** This same FAW Rear Axle Sensor Logic Assembly provides the “logic” for acceleration. If the 6×4 tractor is on a split-traction surface (e.g., one wheel on ice, one on pavement) and the driver accelerates, the wheel on the ice will spin uselessly, wasting power. The ECU sees this “spin-up” (one wheel spinning much faster than the others) via the sensor signal. It then can automatically apply a small amount of brake to *just that wheel* (or cut engine power). This “logic” fools the axle’s differential into sending torque to the wheel that *does* have traction, allowing the truck to move. This entire safety net is built on the data provided by the FAW Rear Axle Sensor Logic Assembly.

Core Component 1: ‘Wheel Speed Sensor’ (3605360-A6T-S)

The star of the FAW Rear Axle Sensor Logic Assembly is the ‘Wheel speed sensor’ (3605360-A6T-S). The parts list calls for two, one for each side of the drive axle. This is the electronic “pickup” that generates the speed signal.

This is typically a “Hall-effect” or “magnetic reluctance” sensor. Its “logic” is to detect magnetic fields. It is mounted via the ‘Sensor bracket’ (3550117A377-S) so that its tip is positioned a fraction of a millimeter away from the ‘ABS ring’ (a “tone ring” with teeth, which is part of the wheel hub assembly, see Assembly 524/525).

As the wheel hub spins, the teeth of the ABS ring fly past the sensor’s tip. Each “tooth” and “gap” creates a “pulse” in the magnetic field. The sensor reads these pulses and sends them as a digital signal (a “square wave”) to the ECU. The *frequency* of these pulses is directly proportional to the wheel’s speed. The ECU counts these pulses and knows, with pinpoint accuracy, how fast the wheel is turning.

This is the most common failure point in the FAW Rear Axle Sensor Logic Assembly. The sensor itself is a sealed electronic unit, but it lives in a hostile environment. It can be damaged by:

• **Debris:** A buildup of brake dust and metallic “fuzz” from the brake drum on the magnetic tip can block the signal.
• **Damage:** A rock or road debris can strike the sensor or its wiring, breaking the circuit.
• **Air Gap:** If the ‘Sensor bracket’ (3550117A377-S) is bent or corroded, the “air gap” between the sensor and the ring will be too large, resulting in a weak or non-existent signal.

A failure of this sensor will immediately trigger an ABS warning light on the dashboard and disable both the ABS and traction control systems, reverting the truck to standard, non-logic braking. A faulty FAW Rear Axle Sensor Logic Assembly is a critical safety issue.

Core Component 2: The Mounting System (Bracket & Sleeve)

The ‘Sensor bracket’ (3550117A377-S) and ‘Sensor sleeve’ (3550361-6S) are the “Bracket Logic” part of the FAW Rear Axle Sensor Logic Assembly.

**’Sensor bracket’ (3550117A377-S):** This is far more than a simple bracket; it is a **precision alignment device**. Its “logic” is to hold the ‘Wheel speed sensor’ in the *exact* correct position and at the *exact* correct angle relative to the ABS tone ring. The “air gap” (the distance between the sensor tip and the ring’s teeth) is the most critical tolerance in the entire FAW Rear Axle Sensor Logic Assembly.

* **If the gap is too large,** the magnetic pulse from the passing teeth will be too weak for the sensor to read, resulting in a “no signal” fault. * **If the gap is too small,** the spinning ABS ring (which can have a tiny “wobble” or “runout”) can strike the sensor tip, destroying it.

**’Sensor sleeve’ (3550361-6S):** This component’s “logic” is one of protection and precise fit. This “sleeve” is a bushing, typically made of a non-corroding material like bronze, brass, or a high-temperature polymer. The ‘Wheel speed sensor’ is inserted *through* this sleeve, which is itself pressed into the ‘Sensor bracket’. This prevents the sensor body (plastic/aluminum) from corroding and “seizing” to the steel or iron bracket, ensuring the FAW Rear Axle Sensor Logic Assembly can be serviced.

Core Component 3: ‘Wire Guide Bushing’ (3605221-A6T-S)

The final component of the FAW Rear Axle Sensor Logic Assembly is the ‘Wheel speed sensor wire guide bushing’ (3605221-A6T-S). This simple-looking part is a critical “logic” component for reliability.

The sensor wire must run from the wheel-end, along the axle housing, and up to the chassis frame harness. This entire path is a “hostile environment” full of heat (from the brakes and differential), vibration, and flying road debris (rocks, ice, etc.).

This “guide bushing” is a specialized, high-temperature rubber or polymer grommet. It is used to safely pass the wire through a hole in a chassis bracket. Its “logic” is to prevent **chafing**. Without this bushing, the sharp, metal edge of the bracket hole would, under constant vibration, rub through the wire’s insulation. This would cause a short-circuit, grounding out the sensor signal and disabling the ABS. This simple bushing is the “armor” that protects the “nervous system” of the FAW Rear Axle Sensor Logic Assembly.

FAW Rear Axle Sensor Logic Assembly Parts List

The following table provides the complete, detailed breakdown of all 4 components identified in the ‘Rear Axle Sensor Logic Assembly’ (555) diagram for the FAW CA4251P66K24T1A3E5 tractor.

Technical Specifications and Assembly Context

The specifications for the FAW Rear Axle Sensor Logic Assembly are defined by its function as the primary data-gathering tool for the vehicle’s active safety systems. The FAW Rear Axle Sensor Logic Assembly is a high-precision, safety-critical system.