What to do when my Check Engine Light is on?

When a check engine light comes on, don’t panic. Here are four common scenarios.

Why is the check engine light on?

First, let's have a quick look at what the check engine light is. The check engine light illuminates when the engine's computer receives a reading from a sensor that's out of spec (sometimes a cycle of several readings) and registers a "hard code" that indicates a problem, that's the DTCs. When the light is lit up, you should have a code check. In the 90s, the industry adopted OBD-II standards across the board, so all vehicles will display the same trouble codes for the same problems.

The check engine light comes on and stays on.

If the check engine light is on constantly during driving with no noticeable driving or performance problems, there is a permanent fault in the emission control system. When this happens, the computer that controls the emissions system will usually make it so your car runs only in a few lower gears — this is known as "limp-home mode." You should get the car serviced as soon as possible.

The check engine light illuminates, stays on, and there are performance problems.

This means that a vital component of your emission control and engine management system has a serious problem. It usually involves a component or system needed for the vehicle to run at all. In many cases, the vehicle is not safe to drive at all — it could stop or stall out at any moment. It's best to pull over to a safe place and have the vehicle towed to a repair shop for a thorough inspection.

The check engine light comes on and blinks in a steady pattern while driving.

Don't confuse this steady pulsing of the check engine light (usually one or more flashes per second) with a flicker (see above). The check engine light may stay on steadily or it may flash when the vehicle is accelerated. This is very serious. There is a severe failure of the emission control system that is causing the engine to misfire to the point that the catalytic converter is damaged each time the check engine light flashes. It may mean that the catalytic converter is overheating to the point that it will glow red or, in extreme cases, start a fire on the underside of the vehicle. Immediately pull over to a safe place and have your vehicle towed to an automotive diagnostician for repair. 

Decode Check Engine Light Codes with Vehicle Health Monitor

As stated in the first section of the article, you don’t need to panic whenever you see a Check Engine Light is on. Use Vehicle Health Monitor, open ZUS App, switch to Safety Page then hit “Scan”. It will return with the codes and the meaning behind them, then you can decide whether to continue your trip or take it to mechanics. And to clear the codes, please see the instructions here.

Why do some DTCs can't be cleared?

Some codes might be permanent. Permanent DTCs are designed to prevent being cleared without a proper fix. So they can't be cleared in a usual way with the scan tool. The only way to clear a PDTC is to fix the underlying problem with the vehicle that originally caused the PDTC and its corresponding DTC to set, and then allow the vehicle sufficient drive time to re-run the monitor that identified the problem in the first place. When the monitor runs without identifying a problem, the PDTC will clear itself.