Check Engine Lightn

CHECK ENGINE LIGHT – THE BASICS

Basically, the “check engine” or “service engine” light comes on when the ECM has detected a problem with one of its input sensors, or with one of the devices it controls. Generally, the ECM will store a code in its memory (it’s a computer, remember?) that indicates in what area the problem has been detected, causing the light to illuminate.

How (solid, flashing) and when (at start-up only, when driving, etc.) the check engine light illuminates can also be indicative of the severity of the problem. Generally, a flashing problem is more serious.

Passenger vehicles made since 1996 (calendar year, not model year) have Onboard Diagnostics, or OBDII. More often than not, the light is due to an emissions related problem. In fact, much of the reason that your vehicle is equipped with OBD is due to EPA environmental controls.

Technicians connect scanners to your OBD port to extract codes pointing to what areas need to be addressed. There are thousands of codes that can potentially arise. Like VINs some of the digits have universal designations.

FREQUENTLY POSED QUESTIONS:

Can I just get a scanner and fix it myself?

Well, you can try that.

But remember:

The stored codes (and there may be many) will define the symptom, not the root of the problem. For example, one of the codes extracted may say that the Oxygen Sensor has low voltage. That does not necessarily mean that the O2 sensor is malfunctioning or needs replacement. It is indicating that something or some things (this where training and experience comes in handy) is or are causing the O2 sensor to behave as if it has low voltage.

AI –artificial intelligence... computers can only act on input, in this case input sensor readings.

OBD is not a complete diagnostic. It is but a step in the diagnostic process. It may tell the technician what area or part is not functioning up to specs. However, it will not reveal if indeed it is the part, or several, or another contributing factor down the line. Something as simple as a loose gas cap can cause your “check engine” light to illuminate. We not only know troubleshooting sequences, have experienced an array of problems from the usual to the quirky, we also have manufacturers’ data and TSBs at our fingertips. A TSB may prove that your problem is covered by your manufacturer’s warranty. We will always let you know if your vehicle has a no cost solution – regardless of whom is responsible.

My “check engine” light came on, but then it went off. What’s up?

Most likely your vehicle was experiencing a problem when the light illuminated. The problem is intermittent, so the light only comes on when the computer is getting abnormal readings from the input sensors.

But the OBD is a computer; it’ll remember what was out of specs, right?

Yes, and no.

The OBD will take a freeze frame shot of the malfunction and put it in memory. However, the memory will clear itself after about three cycles. Cycles are full sequences of operation (cranking, starting, idling, first gear, etc.).

OK. What do I do and how soon do I need to do it?

Solid illumination – Chances are that you notice no driveability problems. Your engine is using OBD to compensate for components out of specs. You are not in dire danger, but your vehicle is not running as efficiently (or cleanly) as it should.

In some cases, the car’s computer may be monitoring the vehicle for maintenance service. You should schedule an appointment as soon as practical. But! Do not ignore it! A small repair can easily snowball into a large one. Take a little bit of time now, and save yourself heartache later.

Flashing lights – Check you guages; if you have low oil pressure or high temperature, pull over as soon as it is safe to do so. If you can not get off the road, reduce speed. Next reduce your load. Bring to a qualified service technician as soon as possible. In some cases, your car's computer may reduce power for you (or go into “limp mode”, attempting to limit the risk of damage.

It bears repeating: DO NOT IGNORE YOUR CHECK ENGINE LIGHT. Yes, even if it seems fine.

As Travis and Williamson counties begin mandatory emissions testing, you should be aware that an illuminated “check engine” light may warrant automatic failure.

And no, disconnecting your battery won’t make it go away. (In some cases the light might be reset, but the code will still be in memory) Also, disconnecting the battery will cause the engine to run a little erratically until the computer can “re-learn” it's previous state.