FAW Electronic Control System Sensor Logic Assembly: A Comprehensive Guide to 7 Key Components

Welcome to this comprehensive technical guide on the FAW Electronic Control System Sensor Logic Assembly. This is the complete set of “senses” for the engine’s main computer (ECU) on the FAW Jiefang CA4251P66K24T1A3E5 6×4 diesel semi-trailer tractor.

The FAW Electronic Control System Sensor Logic Assembly is the “nervous system” that provides all the critical data the ECU needs to make decisions. It monitors engine speed, boost pressure, air temperature, oil pressure, and coolant temperature, and also includes the wiring harness to control the engine brake and injectors.

This guide is an essential resource for professional technicians, fleet managers, and engine specialists. We will deconstruct the entire FAW Electronic Control System Sensor Logic Assembly into its 7 serviceable units, explaining the function of each critical sensor and how they work together to ensure optimal engine performance, efficiency, and safety.

The Master Sensor: Crankshaft Position Sensor (3602120-59D)

The ‘Crankshaft Position Sensor Assembly’ (3602120-59D) is the single most important sensor in the entire FAW Electronic Control System Sensor Logic Assembly. Without a valid signal from this component, the engine’s ECU is “blind” and will not fire the injectors, preventing the engine from starting.

This sensor is a magnetic “Hall effect” or “variable reluctance” pickup. It is mounted in the engine block with a precise air gap (secured by a ‘Hex flange bolt’ Q1840616), pointing at a “tone ring” on the crankshaft. This tone ring is a wheel with a specific pattern of teeth (e.g., 60 teeth with 2 missing). As the crankshaft spins, these teeth fly past the sensor, generating a precise digital pulse for each tooth.

This pulse train gives the ECU two critical pieces of data: first, by timing the pulses, it knows the exact engine RPM. Second, by sensing the “gap” from the missing teeth, it knows the exact rotational position of the crankshaft (e.g., Cylinder 1 is at Top Dead Center). All injection timing and ignition logic is based on this master signal. A failing crankshaft sensor in the FAW Electronic Control System Sensor Logic Assembly will cause misfires, stalling, or a no-start condition.

The Boost Sensor: Intake Air Pressure/Temp Sensor (3602105-59D)

The ‘Intake air pressure temperature sensor assembly’ (3602105-59D) is the second most important sensor for engine performance in the FAW Electronic Control System Sensor Logic Assembly. This is a “T-MAP” or “combo” sensor, meaning it combines two different sensors into one housing for efficiency.

**1. Pressure (MAP):** The “Manifold Absolute Pressure” sensor measures the air pressure *inside* the intake manifold. This tells the ECU how much “boost” the turbocharger is producing. The ECU’s logic map has a “target boost” for any given throttle position and RPM. It compares this target to the *actual* boost reading from this sensor and then modulates the turbocharger’s wastegate to match. This is the heart of electronic boost control.

**2. Temperature (IAT):** The “Intake Air Temperature” sensor (a thermistor) measures the temperature of the air *after* it has passed through the intercooler. Hot air is less dense (less oxygen) and requires less fuel. Colder, denser air requires more fuel for a proper air-fuel ratio. This sensor allows the ECU to fine-tune the fuel mixture for maximum efficiency and power. A faulty T-MAP sensor in the FAW Electronic Control System Sensor Logic Assembly, often clogged with oil from the crankcase ventilation, will cause low power, high smoke, and poor fuel economy.

The Temperature Sensor: Coolant Temp Assembly (3602160-59D)

The ‘Coolant temperature sensor assembly’ (3602160-59D) is the main “thermometer” for the engine, a key component of the FAW Electronic Control System Sensor Logic Assembly. It is a thermistor, a resistor whose electrical resistance changes predictably with temperature. It is threaded directly into a coolant passage on the cylinder head or thermostat housing.

This sensor’s data is used for three critical logic paths. First is “cold start enrichment.” When the ECU sees a cold temperature, it enters “warm-up” mode and injects extra fuel, similar to a choke on an old engine. Second, it controls the “open/closed loop” transition, telling the ECU when the engine is warm enough to rely on its emissions sensors.

Third, and most importantly, is engine protection. This sensor tells the ECU when to activate the high-speed cooling fans. If the temperature continues to climb past a critical point (e.g., 110°C), the ECU will trigger the “overheat” warning light and may enter “limp mode,” de-rating the engine’s power to prevent catastrophic damage like a cracked head or warped block. This sensor from the FAW Electronic Control System Sensor Logic Assembly is a vital part of engine protection.

The Safety Sensor: Engine Oil Pressure Assembly (3602185-48D)

The ‘Engine oil pressure sensor assembly’ (3602185-48D) is the engine’s primary safety switch. It is a simple but non-negotiable part of the FAW Electronic Control System Sensor Logic Assembly. This sensor is a pressure transducer, threaded into the engine’s main oil gallery (after the pump and filter). It converts the physical oil pressure (PSI or Bar) into an electrical signal that the ECU can read.

This sensor’s logic is simple: “is there pressure, or is there not?” The ECU’s programming has a “pressure map” that knows the minimum safe oil pressure for a given RPM. If the sensor’s reading ever drops below this critical threshold, the ECU immediately takes protective action.

This action includes illuminating the red “Stop Engine” light and sounding an audible alarm. In most modern systems, the ECU will also start a timer (e.g., 30 seconds) and if the pressure does not recover, it will *forcefully shut the engine down* to prevent the bearings from melting and the engine from seizing. A faulty sensor in the FAW Electronic Control System Sensor Logic Assembly can be a major problem, either causing nuisance shutdowns or, worse, failing to report a real, catastrophic loss of oil pressure.

The “Nerves”: Engine Brake & Injector Harness (3724850-81D)

The ‘Engine brake & injector wiring harness assembly’ (3724850-81D) is the most physically complex part of the FAW Electronic Control System Sensor Logic Assembly. This is the main “engine-mounted” harness that routes all the critical *output* signals from the ECU to the engine’s primary actuators.

Its first job is to carry the six high-current, high-voltage, precision-timed signals to the electronic fuel injectors. These are the “fire” commands that the ECU calculates based on all the sensor inputs.

Its second job, as indicated by its name, is to control the engine brake (e.g., “Jake Brake”). It routes the “on/off” signal from the driver’s switch (via the ECU) to the electronic solenoids located in the valve train, which in turn activate the engine braking mechanism. This harness is the physical “logic assembly” that makes the FAW Electronic Control System Sensor Logic Assembly‘s decisions a reality.

This harness lives in the worst possible environment: bolted to a vibrating engine, it is subjected to extreme heat, oil, diesel fuel, and moisture. Over time, connectors can become brittle, and the insulation can chafe, causing an electrical short or open. A fault in this harness is a common cause of a “dead” cylinder, a misfire, or a non-functional engine brake. A complete FAW Electronic Control System Sensor Logic Assembly diagnosis must always include a check of this harness.

FAW Electronic Control System Sensor Logic Assembly Parts List

The following table provides the complete, detailed breakdown of all components identified in the ‘Electronic Control System Sensor Logic Assembly’ diagram for the FAW CA4251P66K24T1A3E5 tractor. This FAW Electronic Control System Sensor Logic Assembly is the complete “nervous system” for the engine.

Technical Specifications and Assembly Context

The specifications for the FAW Electronic Control System Sensor Logic Assembly are defined by its function as the complete set of data inputs and key outputs for the Engine Control Unit (ECU). The FAW Electronic Control System Sensor Logic Assembly is a collection of high-precision sensors.