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Modern cars are full of all kinds of chips, wires, and sensors. They all have their function and synchronize into an orchestra of signals to give the car’s onboard computer a realtime evaluation of your automobile’s health and performance. Like all electronics, however, they can degrade over time.

The ECU, or Engine Control Unit, is the conductor of this electrical orchestra. Its a little black box with a bunch of wires coming out of it going to different sensors all over the car. Some of these sensors have a great effect on fuel economy. Their readings determine the amount of fuel the injectors feed into the combustion chamber, and thus affect the power and efficiency of the engine. However, over time some of these sensors can start to relay false readings back to the ECU. This results in lower fuel economy.

Some of the sensors that can affect fuel economy:

• Mass Airflow Sensor (MAF) – This sensor determines how much air is entering the engine. Since the density of air can change in different temperatures and pressures (Boyle’s Law) the engine needs to know how much oxygen is getting into the combustion chamber. Dust and other fine debris that can squeak through the air filter can gum the sensor up and throw off readings.
• Throttle Position Sensor (TPS) – This sensor gives the ECU a realtime reading on the position of the throttle body. The throttle body is a butterfly valve that opens as you press the accelerator. The ECU uses this sensor to determine the acceleration speed and position on the throttle, along with readings from the MAF sensor to determine both injection timings and volume of fuel. If this sensor relays wrong information, it can cause the engine to run more rich or more lean than it should, and under extreme circumstances can lead to stalling or flooding.
• Exhaust Gas Recirculation (EGR) – The EGR sensor controls the workings of the EGR valve that allows the exhausts to recirculate into the incoming air stream and allow recombustion of the exhaust gases. This allows for a more complete burn of the oxygen present in the exhaust gases and also cuts down on the amount of nitrous oxides present in the exhaust gas. If this sensor fails the normal percentage of exhaust gases won’t recirculate and the engine could run out of balance yielding lower fuel economy and performance and possibly failing emissions.
• Oxygen Sensor (O2) – The ECU needs to know how efficient the the engine is performing at all times. It uses an Oxygen sensor to determine if the fuel mixture is optimal. If the O2 sensor registers too much oxygen it will either close off some oxygen supply or tune the amount of fuel the injectors deliver to the combustion chambers. A Faulty O2 sensor will cause the engine to run too lean or too rich depending on which way its out of calibration.

The collaboration of all these sensors with the ECU provide modern engines with great fuel economy and performance, when they are working in concert with each other. Once a sensor goes out, the ECU can only compensate so much before performance and economy start to suffer. Luckily, most of these sensors are easily replaced either by yourself if you’re mechanically proficient, or by your qualified mechanic. If you feel you might be losing fuel economy or your Check Engine light comes on, have the sensors checked.

If you have any other electrical tips for increasing or sustaining a car’s fuel economy, please leave a comment.