A Definitive eBay Buyers Guide for ECUs/Computers in Cars

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A Definitive eBay Buyer's Guide for ECUs/Computers in Cars

The statement that the spacecraft which took Apollo astronauts to the moon had less computer capabilities than today's automobiles is definitely true. An ECU on a fuel-injected vehicle performs by far more functions than anything launched into space in the late 1960s and early 1970s. Late-model vehicles use multiple computers to monitor the function of the engine, transmission, air conditioning system, and vehicle electrical systems, as well as the driver's convenience and comfort options.

Understanding the terminology and basic technology associated with onboard vehicle ECUs and computers is something vehicle owners can benefit from. Being informed on how a vehicle uses the information provided by its computer systems allows vehicle owners to recognise replacement parts. One can purchase vehicle ECUs from auto parts suppliers, used auto parts vendors, and automotive repair shops; however, many buyers shop for automotive computers on eBay, where sellers offer both new and used units for sale at competitive prices.

Understanding Vehicle Computer Terminology

Vehicle computers are generally given an acronym that identifies the component. For example, ECU stands for electronic control unit. Understanding the terminology manufacturers use when they name vehicle computer components can help consumers to better identify what the part is and which vehicle systems the computer monitors and controls. The following table provides a quick reference for consumers regarding vehicle computer nomenclature.

Computer Acronym

Computer Name

System Monitored



Electronic control unit or engine control unit

Electronic control module or engine control module

Engine components and sensors


Climate control unit

Air conditioning



Body control module

Convenience control module

Door locks, power window, interior lighting

ABS Controller

Anti-lock brake system control unit


Yaw Module

Stability control module

Suspension and steering

SRS Module

Supplemental restraint system module



Transmission control unit

Engine and transmission

While these are the most common modules found in late-model vehicles, there are a number of other computers that control individual aspects of vehicle components, such as cruise control and vehicle entertainment systems. Some control units are referred to as control modules, like the ECU and ECM.

Understanding the Function of Vehicle Computers

Most vehicle computers receive input from a number of different sensors and control the functions of multiple components on the vehicle. Understanding the function of vehicle computers as they relate to specific sensors and vehicle systems helps consumers see the correlation between a system malfunction and the control unit that operates that aspect of the vehicle.


Whether you call it an electronic control unit or an engine control module, the primary function of an ECU is to read a number of different sensors on the engine and transmission and to use that input to control certain engine and transmission functions. The following chart lists the most common functions of an ECU by showing the sensors that are monitored, what the sensors detect, and how the information provided is used.


Sensor Detection

Information Provided

Throttle Position Sensor (TPS)

Throttle pedal movement

Driver speed request translates to injector volume

Mass Air Flow Sensor (MAS)

Engine air intake

Air/fuel mixture ratio for optimum fuel efficiency

Coolant Temperature Sensor

Engine coolant temperature

When cold the fuel mixture is richened similar to a choke

Knock Sensor

Engine timing

Advances or retards engine timing for maximum performance and efficiency

Idle Speed Control Motor or Stepper Motor

Engine Idle Speed

Maintains idle speed, adjusts for cold starts and additional loads like A/C compressor engagement

Crankshaft Position Sensor

Engine timing

Helps to coordinate valve timing with injector spray and ignition spark

Oxygen Sensor

Vehicle emissions

Monitors exhaust emissions and helps to adjust the air fuel mixture

ECU input from the TPS signals the transmission to downshift to a lower gear when more torque is required. The coolant temperature sensor and the idle speed control motor work together to perform the functions of a choke during cold-start conditions. Fuel delivery to the injectors feed injector spray pulses, which are coordinated with intake valve openings and the firing of spark plugs on the compression stroke of the piston. A computer chip in the control unit processes all the information and reads outputs for a table programmed into the chip. Some drivers desirous of increased performance replace the stock chip with a high-performance chip that changes the characteristics of the output table and produces more horsepower and torque from the engine.

Climate Control Units

For vehicles equipped with electronic climate control, drivers have the option to manage the A/C and heater controls themselves or to allow the automatic temperature control (ATC) to do it for them. By receiving input from the in car temperature sensor, outside air temperature sensor, the ambient air temperature sensor, and the sun load sensor, the ATC determines a comfortable setting for the heater or air conditioner. The climate control unit also determines which duct vents to open and close, thereby directing the hot or cold air to the area of the passenger compartment that benefits most from the change in temperature. Blower speeds are also controlled to provide the necessary air flow through the passenger compartment to reach the ideal comfort level for the temperature range selected.


The body control module or convenience control module operates a number of passenger luxury components. Keyless entry, remote start, vehicle security systems, sliding doors, and vehicle lighting systems are some of the vehicle features controlled by the BCM. Most power accessories such as seats, windows, locks, and mirrors are also components that the BCM helps to operate.

Anti-Lock Brake Controls

Amongst the most important vehicle controls are those that control the anti-lock brake system. Individual wheel speed sensors provide input to the ABS controller, which then calculates differences between the four wheels caused by wheel slip or skid. The controller operates a pump and series of valves that provide hydraulic pressure to the brakes individually to bring the vehicle to a safe stop. Instead of the driver having to pump the brake pedal to prevent the wheels from locking and skidding, the ABS controller performs the function faster, more efficiently, and more precisely to the individual wheels.

Yaw Module

Yaw is a not-so-common term that is used more often in a nautical sense or to describe the pitch of an aircraft. When a car experiences yaw, it weaves or swerves; this sudden movement is detected by the yaw sensor and activates the vehicle's stability control system. By monitoring wheel speed sensors and steering wheel position sensors, the stability control detects instances of oversteer or understeer and, using the hydraulic brake system, can actually steer the vehicle by braking one or more wheels to correct the slide or skid.

Supplemental Restraint System

The SRS module controls the activation of airbags located throughout the vehicle. Sensors in the bumper and, if so equipped, in the doors register the force of the impact and trigger the airbags to fire their inflator if they register sufficient force. Airbag wiring and airbag connectors are easily identified by their yellow colour; this prevents accidental activation by probing into those circuits.

Transmission Control Unit

The TCU works in conjunction with the ECU to monitor the operations of sensor and uses the input to control transmission shifting. By analysing data provided by the vehicle speed sensor, wheel speed sensors, the TPS, and a number of internal transmissions sensors; the transmission control unit signals the upshifting or downshifting of gears in the transmission. The control unit also tells the transmission when to drop into overdrive to maximise fuel economy.

Buying ECUs and Vehicle Computer Modules on eBay

With many sellers offering automotive computer modules and related components for sale, eBay is your one-stop marketplace for vehicle control units and input sensors. Buyers can find new, used, and refurbished vehicle computers from the large selection of automotive parts that eBay has to offer. Buying automotive parts on eBay is convenient and far easier than driving around town searching for the right part to match your vehicle.

It is not a difficult task to locate the exact part for a particular vehicle. From the eBay Motors page, enter the make and model of the vehicle in the drop-down selection boxes; then, enter the name of the part you are looking for into the search bar and click search to bring up all of the matching listings. You can communicate with sellers by clicking on the provided link in the listing to inquire about specifics of the part or other questions pertinent to the sale. You can be assured of a safe and secure transaction between yourself and the seller by using PayPal to complete the purchase online.


Automotive technicians rely on the vehicle's onboard computers to provide information that helps diagnose component malfunctions and failures. Diagnostic computers are often required to gather the coded information from the vehicle's computer in order to analyse the data. Sometimes the problem the vehicle is displaying is a matter of faulty information provided by a defective sensor; occasionally the computerised control unit fails and must be replaced.

If consumers understand how control modules process the information that sensors provide, they will recognise symptoms as they relate to the failure of specific components. For example, if the vehicle's idle speed is fluctuating, then the idle speed control motor is a good starting point in the diagnostic process. Component sensors reading out of range often triggers the ECU to activate an indicator light; this check engine light illuminates in the instrument cluster to advise the driver of a potential problem. By using a scan tool, technicians retrieve a code from the ECU that indicates which component is reading out of range, and by following published diagnostic diagrams can track the failure to the specific component causing the problem.

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