Sensors & Electrical System – Complete Guide for Engine Diagnostics

Sensors • Wiring • ECU Signals • Accurate Diagnostics

Sensors & Electrical System – Complete Guide for Engine Diagnostics

Modern vehicles rely heavily on engine sensors and electrical systems for performance, fuel efficiency, and emission control. Understanding sensor working principles, actuator testing, and electrical diagnostics is essential for accurate vehicle troubleshooting.

This guide covers engine sensors, SCR & EATS sensors, actuator testing, multimeter testing, voltage & resistance checks, and engine starting problems.

🔍 Engine Sensors 🌍 SCR / EATS Sensors 🔧 Actuators Testing 🔌 Multimeter Tests ⚡ Voltage & Resistance 🚗 Starting Problems

🔍 Engine Sensors – Types & Working Principle

Engine sensors monitor various parameters and send signals to the ECU (Engine Control Unit) to optimize engine performance.

MAP Sensor (Manifold Absolute Pressure)

Measures intake air pressure
Helps calculate fuel injection

MAF Sensor (Mass Air Flow)

Measures air entering engine
Controls air-fuel ratio

Oxygen Sensor (O2 Sensor)

Monitors exhaust gases
Improves fuel efficiency

Crankshaft Position Sensor

Detects crankshaft speed
Controls ignition timing

Camshaft Position Sensor

Syncs fuel injection timing

Coolant Temperature Sensor

Monitors engine temperature

Throttle Position Sensor (TPS)

Detects throttle opening angle

⚙️ Working Principle of Engine Sensors

Most sensors operate on:

Voltage signal variation Resistance change Magnetic induction Hall effect principle

The ECU receives sensor data and adjusts:

Fuel injection Ignition timing Turbo boost Emission control

🌍 SCR Sensors & EATS Sensors Explained

SCR

SCR (Selective Catalytic Reduction) Sensors

Used in diesel engines to reduce NOx emissions.

Key SCR Sensors:

NOx Sensor DEF Quality Sensor Temperature Sensor Pressure Sensor

✅ Function: Monitor exhaust gases, control AdBlue/DEF injection, and reduce harmful emissions.

EATS

EATS (Exhaust After Treatment System) Sensors

EATS includes: DPF, DOC, SCR system

Sensors Used:

Differential Pressure Sensor Exhaust Gas Temperature Sensor NOx Sensors

These sensors ensure compliance with emission norms like BS6, Euro 6, etc.

🔧 Actuators Testing – Complete Guide

Actuators convert ECU signals into mechanical movement.

Common Engine Actuators

Fuel Injectors EGR Valve Turbo Actuator Throttle Body Idle Air Control Valve Cooling Fan Motor

Faulty actuators can cause: power loss, rough idling, black smoke, poor acceleration.

Testing Methods

Scan tool activation test
Direct power supply test
Resistance measurement
Signal voltage testing

🔌 Multimeter Testing – Practical Guide

A multimeter is essential for diagnosing electrical faults.

Basic Multimeter Tests

Voltage Testing Resistance Testing Continuity Testing Diode Testing Current Measurement

✔

Always Follow

Use correct range settings
Disconnect battery when necessary
Follow wiring diagrams

⚡ Voltage & Resistance Testing Explained

🔋 Voltage Testing

Check battery voltage (12.6V ideal)
Sensor reference voltage (5V typical)
Alternator output (13.5V–14.5V)

Low voltage may cause: starting issues, sensor malfunction, ECU errors.

🔎 Resistance Testing

Test sensor resistance values
Check wiring continuity
Compare readings with manufacturer specifications

Abnormal resistance indicates: open circuit, short circuit, damaged sensor.

🚗 Engine Starting Problems – Electrical Causes

Starting issues are often linked to the electrical system.

✅

Common Causes

Weak or dead battery
Faulty starter motor
Bad ignition switch
Crankshaft sensor failure
Fuel pump relay problem
ECU malfunction
Loose wiring or grounding issue

🔧

Engine Starting Diagnosis Steps

Check battery voltage

Inspect starter motor operation

Scan ECU for fault codes

Test crankshaft sensor signal

Check fuel pump voltage

Verify ignition system

✅ Early diagnosis prevents breakdowns and costly repairs.