The ECM "Check Engine"
It all starts when you see the “Check Engine” light. Now you know something isn’t right. The next stop is your service technician who has the equipment and tools to find and fix the problem.
When it comes to certifying that your car meets emissions standards, many states rely on the OBD II Engine Control Module (ECM) to certify vehicles. Basically, the ECM checks and verifies the functional integrity of your car’s systems, ultimately checking to ensure that the state’s emission standards are being met.
ECMs perform three basic types of tests: circuit integrity, the rationality test and the functional test. The circuit integrity test looks for open circuits, shorts to the power or to the ground. For the rationality test, the ECM compares the information from one sensor to another to see if they are compatible. A great example is when the ECM detects how much air should be flowing with any given throttle opening. By comparing the Throttle Position Sensor (TPS) signal to the Mass Airflow sensor (MAF), the ECM can detect and report any discrepancies.
The functional test is one the ECM actually tests the performance of a component or system. There are two types, the passive and the intrusive. If the test is conducted under normal operating conditions with no direct involvement of the ECM, it’s a passive test. If, however, the ECM takes an active role in altering the normal operating conditions, then it’s an intrusive test.
A great example of a functional test involves the Evaporative Emissions systems (EVAP). A natural vacuum leak detection system is passive since the ECM is simply observing and reporting on the normal operation of components. The test becomes intrusive when the ECM commands the vent closed and applies engine vacuum to the system before monitoring the resulting vacuum decay.
Your technician reads the results of the ECM tests, and there are three possible results: ready, not ready or not supported. Additionally, the ECM conducts what is called a drive cycle or trip, meaning all the criteria have been met and all the monitored tests have been completed.
So the big question becomes, as a consumer, how does this benefit you? When your service tech is an expert at utilizing this diagnostic tool, problems can be quickly and accurately detected, and then efficiently tested to ensure the repair has been successfully made. And the majority of the time, such a diagnosis and repair can be done within the service bay without having to take your vehicle for drives in an attempt to detect and replicate the problem in the first place.
The bottom line is the ECM is an excellent diagnostic tool, and by having a service technician who expertly understands this tool’s capabilities, the ultimate benefactor of this knowledge is you.
Johnny Nocera has been on the radio airwaves in Southwest Florida with “Dr. Johnny’s Car Clinic” WGUF New Radio 98.9 FM every Saturday morning from 9-10 for over 27 years. He also owns, along with his sons Jr. and Jimmy, Supreme Auto and Collision located in downtown Naples, and has been in business for more than 38 years.