Engine Sensors Demystified: What They Are, What They Do, And Why You Need Them.

Understanding the various engine sensors on your car, truck, or SUV and how they function can really help you to save money and make better and more informed decisions regarding the care and repair of your vehicle.

Almost all cars, trucks, SUVs and other vehicles manufactured within the last 25 years or so utilize a type of onboard computer which manages engine functions such as Ignition Timing, Fuel Delivery, Exhaust Gas Recirculation (EGR), Air Intake, and some other functions. In order for an Internal Combustion Engine to run properly, it needs 4 basic things: Fuel, Air, Compression, and Ignition. Fuel and air must be delivered in precise quantities and at specific intervals. For optimum performance and economy, this fuel/air mixture must be ignited within each cylinder at exactly the correct instant.

Until about the mid 1970s, these things were mostly managed by various and sometimes complicated electro-mechanical systems which needed frequent maintenance and adjustment. It was realized long ago that these items could be better and tighter managed via some electronic means such as a small computer which could be designed for the task. But various means were also needed in order to supply the computer with information about engine operating conditions at any given instant. This would allow the computer to make decisions and thereby make rapid adjustments via various actuators in order to maintain optimum engine performance and fuel economy under all conditions.

This is where the engine sensors come in. Their job is to monitor engine parameters and pass information (in the form of analog electrical signals) back to the engine computer for processing. In a modern vehicle there are several types of engine sensors which monitor engine temperature, intake air temperature, intake air flow rate, crankshaft position, engine speed, vehicle speed, exhaust oxygen content, and several other processes.

It is very important that all of these sensors are always working correctly because if not then they will send incorrect data to the engine computer, which will then try to compensate by readjusting the various engine parameters. If certain engine sensor readings become too far outside of limits which are established by software within the engine computer, the computer will usually default to a set of basic (or “panic”) values and will no longer manage the engine until the problem is corrected – i.e. the affected sensor is either repaired or replaced. And while the engine computer is using these basic values, fuel economy and performance will suffer.

Generally, an engine sensor which becomes defective or disconnected will cause the “Check Engine” light to illuminate and will also set or store a specific trouble code in the engine computer. These codes can then be retrieved and studied by using a special tool which is made for the purpose, and you can then use that information to help isolate the trouble.

Engine sensors are not necessarily expensive – some cost more than others – and they can often be replaced by the home mechanic. If you do the work yourself, you will need certain service information about your vehicle. The service information will show you the locations of the various sensors, specific replacement procedures, and sometimes will also show testing procedures for the sensors as well.