Check Engine Light is On
The ‘Check Engine’ warning light can be the most problematic experience for any driver using a modern car from 1996 onwards. The problem with most cars is that the Check Engine, or MIL (Malfunction Indicator Lamp) does nothing more than tell the driver that something is wrong. Only some fine luxury cars give additional information through their On-Board Display about that particular problem. For the majority of other vehicle owners of less expensive, luxury cars / trucks this can be a real problem. To make matters worse, sometimes when the MIL goes On, the engine will seem to be running perfectly — like a ‘Swiss clock’.
The Check Engine Light Explained
The OBD II system, which was an official updated version of the previous OBD1 (excluding the temporary introduction of the Obd 1\.5 from some vehicle manufacturers) had an absolute priority; this being ‘to always be environmentally clean’.
Mainly the function of the OBD system and the parameters of its software were designed so that the engine will always run on a controlled, strict level of emissions standard. To achieve this the engine has to have various information from all the components and reciprocating parts, including the emissions being thrown out of the exhaust ports. Usually these sensors are very sturdy and do not require constant or frequent maintenance, unlike the classic points of an old distributor, as an example. Still these sensors live in a harsh environment, and will eventually deteriorate, giving false readings as they break down.
Some of these worn out OBD2 sensors will be intermittent failures, while others will be a constant failure.These in turn will create a flag to the Powertrain Control Module (PCM), or Engine Control Unit (ECU), meaning the system stores this data with it’s correspondent code. In turn the MIL light goes On to warn the driver of a problem. The only way to see what this fault is, without any expensive guess-work is to have some sort of communication device with the OBD system. These can be anything from the simplest readers to the more sophisticated diagnostic OBD2 scanners. After the fault code or codes are retrieved from the particular scantool being used, the next thing is to make an in-depth diagnosis, before changing the said offensive part.
How to do a proper diagnostic check and repair
So normally the procedure goes like this:
| 1. |
Check the faulty sensor visually for any signs of external damage. |
| 2. |
Check sensor connection is tight. Remove and inspect both male and female plugs for any contamination or corrosion. |
| 3. |
Take a live scan reading, recording the live data if possible (voltage and voltage variations). |
If nothing is found:
| 1. | Mentally isolate the whole circuit system from the rest of the circuit. |
| 2. | Start a full inspection of the circuit from beginning to end, using the backward method. Last component first, moving your way down to the first component. |
| 3. | You may need to take some additional readings (and take notes of these results) of the components in the process. |
If nothing is found after these in-depth diagnosis, the indicated sensor is most probably damaged and might be giving an intermittent fault. Never assume that a part is bad just by pure guess-work, or by just having a code which translates to a particular part/sensor, and change without any further inspection. You will be surprised by how much less money you’ll spend in new parts — not to mention repeat faults resurfacing after a few hours, days or weeks.
Ever wondered about people speaking of repeat fault codes appearing as “ghosts” in later time, even after new parts were installed. Well, now you know why.
Repairing the confirmed fault
Now that you have checked the fault code, inspected the sensor/s and the remaining components of that particular circuit, eliminating most chances of any false readings, or data it is time to replace that sensor or component.
| 1. | Buy an exact factory specification part — original if possible, or a good quality aftermarket with the factory specifications. |
| 2. | Change the faulty sensor or component with the new part, taking care of any plugs, hoses you might need to remove to access the offending part. |
| 3. | Give a final inspection in the area you worked on after completion for any loose or unattached wiring, plugs connections or anything else. |
| 4. | Reset the fault from the PCM and test run the vehicle sensibly (without assuming the fault is completely eliminate — so no test pilot drives). |
| 5. | If no Check Light appears you are done! — Congratulations for your OBD repair. |
By now you should be quite aware that these OBD systems cannot be tackled blindly, without the proper information. So a type of scan-tool is necessary for this information to be brought to light. If you are not doing the repairs yourself it is still worth buying a good quality, but less expensive reader with minimum functions. This way you can have the fault codes before going to your auto technician so that you can assure yourself that you are not being cheated by blind part-swapping. If you intend to do the repairs yourself it is your wisest choice to buy the best diagnostic obd2 scanner you can afford. It will eventually pay off for itself when it comes to use. Consider that purchase as a small investment towards your vehicle, like when buying other quality hand-tools.
