Today we’re going to talk about on-board diagnostics and the questions we hear from viewers who need answers about diagnostic services. They want to know what diagnostics are, what’s involved and what the benefits are. They really want to understand the value of diagnostic scans by a trained technician.
These are valid concerns. If you don’t understand something it’s really hard to know its value. Let’s start with some history.
Since 1996, all cars and light trucks have been required to use a standardized diagnostic system to help repair technicians determine what’s wrong with your vehicle. The diagnostic system works with the vehicle’s Engine Control Module – the computer that controls many engine functions.
The computer monitors dozens of components and processes. Depending on what the sensors read, the computer will make adjustments to compensate for conditions and minor problems. When there is a condition that it can’t adjust for, the computer will turn on the check engine light.
It is also called the “service engine soon” light on some vehicles. The warning light signals you to get into a service center so that the trouble code can be read and the problem can be fixed. Your service center will have a scan tool and powerful software that will help the technician diagnose the problem.
If you’ve searched for check engine light on the internet, you may have seen that you can buy an inexpensive scanner or go to an auto parts store to have the trouble code read to tell you exactly what’s wrong.
That’s a common myth. The code itself doesn’t tell you what’s broken. It starts you looking in the right place. It tells you what engine parameter is out of range – but it won’t tell you what’s wrong or how to fix it.
Let’s say you think your daughter has a fever. You take her temperature and it reads one 102 degrees. You’ve confirmed a fever, but you don’t know what’s causing it. Is it a 24 hour flu, an infection, appendicitis or leukemia? A fever is a symptom of all of these medical problems, but it takes a skilled physician’s examination and additional diagnostic tests to find out what is actually causing the fever.
An example of a trouble code could be: P0133, which reads “Bank 1 sensor 1 circuit slow response”. This means that the front oxygen sensor has a slow response time to changes in the air-fuel mix. If that’s all you knew about cars, you would think your oxygen sensor was broken and would replace it. Now, it could be the oxygen sensor – but it could also be a bad or contaminated airflow sensor, exhaust leak, electrical problem, an intake manifold leak or any of a number of other things.
You can imagine a lot of oxygen sensors have been replaced because of that code. So the on-board diagnostics point the way to where the trouble lies, but it takes some skill and high-tech equipment to actually pinpoint the problem. The cheap scan tools that a consumer can buy do not have the ability to retrieve some of the operating history that’s stored in the engine control computer. That history’s very helpful in diagnosing the problem. Service centers invest a lot of money in high-end diagnostic tools to help solve the mystery and get you back on the road as soon as possible without replacing a lot of parts that don’t need replacing.
So, on-board diagnostics provide a powerful starting place for a highly-trained, well-equipped technician to get to the bottom of your problem. When your check engine light comes on, get it checked. If the light burns steady – don’t panic. Get in soon to have the engine scanned. A flashing check engine light means that there is a severe engine problem. Get in as soon as you can – waiting too long can lead to very expensive damage. And try to not drive at high speed or tow or haul heavy loads with a flashing check engine light.
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