29 sensors explained

Car Sensors: What They Do and How to Test Them

The engine computer decides how much fuel to inject, when to fire the spark and when to shift gears based on what its sensors report. When one of them lies or stops responding, a trouble code appears. Each page covers function, location, reference values, the multimeter test and related codes.

How a sensor works

  1. It measures a physical quantity: temperature, pressure, position, rotation, airflow or oxygen.
  2. It converts it into a signal: a resistance, a 0 to 5 V voltage, a frequency or a digital message.
  3. The computer compares it with what it expects for the current engine conditions.
  4. If the signal is implausible for the programmed time, it stores a code and turns on the warning light.

A sensor code is not always the sensor

Often the fault is in the wiring, the connector, the 5 V reference supply or the ground. That is why every test starts at the connector: power first, then ground, and the signal last.

Guide: how to test a sensor with a multimeter

Engine position and speed 3

Air and fuel 6

Temperature and oil pressure 3

Emissions and exhaust 8

Transmission 4

Chassis and safety 5