The engine of a modern car is controlled by a computer, aka the ECM – Engine Control Module. This computer needs information from the engine, but also from other part of the car and the environment to work in an optimized manner. This information (or data) is derived from sensors that, by means of a module and the car’s network, supply this data to the ECU that uses this data to control the engine. But many sensors are directly connected to the ECU via the wiring harness.
The main electrical components in a modern car’s electrical system are:
- Sensors
These collect data for one or more modules - Actuators
Activate a function as ordered by a module - Wiring harness
Carries electrical signals throughout the vehicle from sensors to modules to actuators - Modules
Small electronic computers designed to perform a specific task in a car
Sensors:
Engine sensors:
- Oil pressure
- Cooling water temperature
- Engine oil temperature
- Air intake manifold air pressure
- Air intake manifold air temperature
- Gas pedal position
- Throttle position
- Crank axle position
- Cam axle position
- Exhaust gas – before cat
- Exhaust gas – after cat
- Knocking
- Fuel pressure
- Clutch pedal postion
- Brake pedal position
- …*
Transmission sensors:
- Shifter position
- Clutch pedal position
- Vehicle speed
- Engine rpm
- Gas pedal position
- Air intake manifold air pressure
- Reverse gear engaged
- Oil temperature
- …*
Other sensors:
- Ventilation air temperature
- Wheel speed
- Tyre pressure
- Steering wheel position
- Brake pedal position
- Door ajar
- Rear lid ajar
- Hood ajar
- …*
Actuators:
Engine actuators:
- Relays for:
- Starter motor
- Powering the ECM
- Fuel pump
- …*
- Throttle body
- Fuel pump
- Fuel injectors
- Spark plugs
- …*
Transmission actuators:
- Automatic transmission gearlever lock
- Electric valves
- …*
Body shell actuators:
- ABS hydraulic module
- Rear lid actuator
- Electric window motors
- Door lock servos
- Relays for:
- Front lighting
- Rear window heater
- …
- …*
The Wiring harness:
Wiring harnesses tend to be split up in smaller parts that can easily connected rather than one big cover-it-all harness. If split, you can have harnesses for the following:
- Engine
- Fuel injectors
- Transmission
- Instrument cluster
- Inner doors
- Backlid
- Rear part of the car
- Front lights
- …*
Modules:
Modules are small computers and the brain of the operation. But each module is specialized to only run specific tasks:
- ECM
- BCM
- TCM/ATCM
- Ignition modules
- ICM
- ACM/ABSCM
- EBCM
- …*
*Notably, none of these lists are complete, and they probably never will. Due to the speed of automotive technology development in recent years, any list provided today will be obsolete within a single year.
Paul
2025-08
Sweden
This page is part of a series. You can find the main page for the series here.