What To Do With A Check Engine

The Nightmare begins!

So, you get the call. The dash is signaling a check engine. Time to remove the light and sell the truck as fast as possible. Maybe put black tape over the light and pretend that not only is the check engine light not on, but you’re getting better mileage than ever before! While neither is a very good idea, I have, unfortunately, seen both.

Now, there is a better way and it all begins with understanding what triggers a light to come on. Once we understand why a check engine light is triggered we can also understand what needs to happen to fix it and more importantly, how to prevent it.

Every sensor on a vehicle has an acceptable range. From within that range, information is used to make decisions as to how to run the vehicle. I’ll take an engine’s water temperature sensor as an example. I promise this won’t get too technical. This is a typical sensor is using 5 volts. 5 volts come in, depending on the temperature 0-5 volts goes back out.

Only a part of that 5 volts is an “acceptable range”. 0 or 5 meaning there is likely a short, or a cut wire or faulty plug. With that being said, let’s assume for our example that 1-4 volts are an acceptable range. 2 volts may mean 0-degrees or less while 4 volts may mean 400 degrees or more. With that, anywhere between 0-400 degrees is sending a signal of between 2-4 volts, increasing as the temperature does.

5-volt sensor readings.

If a check engine is triggered, then one or more sensors is outside the acceptable operating range, and so the truck is saying, “this doesn’t add up, there is a problem”. This condition may mean the sensor is faulty or there is a wiring problem. But, likely, there is a condition that is considered unsafe, such as the engine overheating.

Hopefully, your driver saw the check engine lamp come on. He was monitoring not just his mirrors and the road ahead, but the many gauges in the dash. Not a single one of the many gauges is there for nothing.

Back to the original question. What to do when a check engine appears.

Yellow/Amber lamp

Let’s take a yellow light. Turn off the radio. You may hear something grinding, a rough idle of the engine, or something else that is not right. The condition may be caused by a mechanical failure and so to prevent excessive damage, the engine needs to be turned off as soon as possible and as soon as is safe. If we don’t hear any abnormal noise or erratic idle. Check the gauges. Oil pressure and coolant temperature above all else. What other gauges do you have? After-treatment temperatures differential, transmission, etc. Can you see the exhaust? As they say, “If it’s smokin, it’s broken”.

Thick black smoke typically means oil is being burnt. White smoke typically means anti-freeze is being burnt. Either condition means you should not continue to operate the vehicle. Today’s trucks are prone to accumulating damage. If the temperatures are excessive, Waiting to cool down to limp to a shop may be possible but you always run the risk of a breakdown and further damage all the same.

Now, let’s say that all the gauges are reading good numbers. There is no smoke coming from the exhaust. There are no abnormal sounds and the engine is idling well. You can still take a few more precautions. When the dash says check engine, you should. As soon as it is safe to do so, pull over. Check for any leaks. Check the oil level. Is the level low, or high? does it smell like anti-freeze? Check the coolant. Is the level good, is it still the same color or is it turning black? Later if you decide to restart the engine are there bubbles coming into the anti-freeze reservoir? These can be signs of internal damage such as a head gasket. Take a quick look around the engine for exhaust leaks, intake leaks, loose collars (be careful it will be hot all around the engine). Is there a wiring harness clearly broken or rubbing that could have broken wires? These are all things that can help give an idea of whether it is safe to get back on the road to a garage.

Red lamp

For a red light, everything is painfully simple. Turn off your engine and pull over as much as possible right now, ask questions later. The red light will only come on if there is a condition that can be detrimental to the engine or the after-treatment system and or could put the truck in a situation that could cause an accident. Either a mobile mechanic or a towing should be brought to either work on the truck, or bring it somewhere where it can be worked on.

Conclusion

It must be said, however, that despite everything “looking” alright, you can’t know until the codes are read and tests are performed. There’s a fine line between an expensive tow because the coolant was low versus assuming or guessing that all is well and causing more damage than there already is and possibly causing an accident. A driver can, however, through diligence and a little know-how save a lot of delays, damage, and costly repairs. It’s all about being prepared and having a plan in advance that can make all the difference.

Drive safe,

Kevin Gauthier