Auto Sensors Diagnostics and Repair

19/04/2022

A must read article or guide about common car sensor troubleshooting and repair for today’s technician or DIY. 

Car Sensors be it input switches, output solenoids, Pressure, Temperature, or Hall effect, are important electronic components that provide or receive information from or to the PCM/ECM or any of the control modules. They are implanted in the car's electrical circuits purposely for engine performance, reduction of emission (pollutants), and gas mileage, as well as provide security and protection. If your engine is performing well it's because your sensors are doing great.

Fixing engine performance, security, and protection issues in today's modern cars warrant the understanding of how these car sensors function, the category they fall under be it input or output device, how they are powered and grounded, and finally the key role the signal wire play.

Checking for power and grounds is basic for all electrical circuit checks and does not change whether you use a Test-light or a digital multimeter. Apparently, if you are not getting source voltage, it’s quite simple to look for the source - be it a fuse, relay or PCM. The same applies to the ground side of the sensor circuit. The power and ground have a fixed voltage reading - either 15 or 2volts for power or <.002volts for grounds

But what about the signal wire? What is it anyway? Are the checks the same as that of the grounds and powers? Can one use a normal test light or digital multimeter to run the checks? Well, not all the time. This changes the entire game in diagnosing signal wires associated with sensors. Adding another diagnostic tool - the Graphing Multimeter or preferably Scope-meter helps easily catch glitches that the basic circuit diagnostic tools cannot. Although the PCM or other control modules only understand and accept voltages and currents to make decisions, one cannot equally use a multimeter to run a car sensor check because these voltages keep changing with respect to what the car sensor is detecting. A technician diagnosing a signal wire will be dealing with waveforms and patterns uniquely programmed by engineers to ascertain whether the car sensor is working perfectly or not. 

Let's pause for a while and talk about this signal. A signal wire is the only wire with changing voltages when measured, that connects always the sensor be it a potentiometer, pressure, hall-effect, or thermistor to the computer (PCM/ECM). Well, that is quite confusing. What about the power and ground wires that are between the sensor and the computer? Good question. You are right but their voltages do not change. 

After Identifying the wire with changing voltages - this signal wire helps you quickly perform a signal circuit integrity check. This check rules out (2/3) two-thirds of the problem, because it eliminates problems that are supposed to show from the PCM/ECM right through the signal wire, and down to the end of the signal wire, which is the output of the sensor. The focus is then shifted to the sensor itself if it passes this circuit integrity test. During this integrity circuit testing, any scan tool with the ability to plot PIDs becomes your most invaluable tool. Every integrity test you perform must reflect on the scan tool as a piece of communication evidence.

Find out more about how to diagnose and fix individual sensors be it switches, solenoids, potentiometers, thermistors, or hall-effects circuits following the links below. We will lay more emphasis on this signal circuit integrity testing per sensor, as well as check for the ground and power.