Ford's "Check Engine" light: What does it indicate?

[Jake]

@bufftabby

You can do what I did to my '95 Ranger: put a piece of black electrical tape over the “Check Engine” light.

(So far, so good. knocks on wood)

Heh. That’s what I did with my "91 Ranger. But after awhile (about a year) it started sputtering and missing under power, so I sold it.

[UltraVires]

@brad_d

California is that way, too. Biennial smog checks are required to register a vehicle, and the Check Engine Light being on is an automatic fail.

I don’t understand this. A “Check Engine” light could mean a million things not related to your exhaust. That seems like a lazy inspection system.

[Gary_T]

@jtgain

I don’t understand this. A “Check Engine” light could mean a million things not related to your exhaust.

But almost all of those things could have an effect on emissions.

[Auntbeast]

Mine comes on every time it is due for an oil change. It seems to be triggered to the mileage. Of course, using synthetic, it is not recommended to change it as often, so it makes the stupid used-to-mean-critical-shit-that-now-means-worthless-shit light even more useless.

[jasonh300]

@fandango

A better question is why can’t they just have a digital LED readout of the code on a car?

On Fords since the mid 90s, if there’s a digital odometer readout, you hold the trip meter button in while you turn the key on and keep holding it until the display changes. (I haven’t done this in a while so I don’t remember what it changes to, but you’ll see it). Then you start the engine and you can cycle through different things on the digital readout such as speed, RPM, temperature, fuel-units left (not in any measuring unit anyone knows about though) and a few other things. At some point, you’ll start seeing letter and number combinations. These are the codes. I’m not sure where you have to go to find out what they mean, but there’s probably an online database that’ll give you the basic information.

I had a couple of Mustangs and a Ford Freestar that I got this to work on. I also got codes to come up on an older F150 that was pre-OBD2. The F150 didn’t show the digital gauge readouts but it showed codes.

[dalej42]

It would fail emissions in Arizona as fell. However, there is no law against disconnecting the battery overnight and reconnecting it in the morning. Often, that makes the check engine light go off. I’ve noticed the one in my 2002 VW Passat will come on if I have to accelerate rapidly.

[1010011010]

@jtgain

I don’t understand this. A “Check Engine” light could mean a million things not related to your exhaust. That seems like a lazy inspection system.

I have a Honda, so the specific meanings may be different for Ford, but a steady CEL means no reading from a sensor in the emissions control system (i.e., the sensor is borked, but the car is probably running fine). A flashing CEL refers to a out-of-bounds reading from an apparently working sensor (i.e., there is something wrong with your engine and it’s currently violating emissions standards).

Read your owner’s manual if you still have it. It will probably explain exactly what conditions give you a CEL (steady or flashing). I wouldn’t be surprised if it’s standardized.

[Rick]

@Gary_T

“Check engine” lights have been standard on all cars decades, not just Ford. They do have legitimate function, which is to make the driver aware that the onboard computer has recognized a problem in the systems that it monitors. Some such problems are serious or potentially serious, others are comparatively trivial. My suggestion is to have a competent shop evaluate it. There are parts store that will read the trouble code for free, and occasionally that’s beneficial, but reading the code is usually just the first step in identifying the actual problem. For example, if the code description is “low EGR flow,” they’ll suggest you replace the EGR valve, but that code is usually caused by clogged EGR passages in the engine or a leaking EGR hose. Generally, you get what you pay for.

On OBDI systems a check engine light is tied to a sensor or system having a fault. In general short to ground, short to power, or open circuit. On OBDII systems the system will also detect when reading are out of line. In either case the increased emissions is the reason for the check engine light. I agree that you get what you pay for.

@Stink Fish Pot

This is a 17 year old car with an old computer. My guess is, like some others have said, that even if an auto parts shop will diagnose the code, that will be pretty vague.

My suggestion (aside from the real one, take it to Ford), is to buy two bottles of Gumout (or a similar product), put them in your gas tank, and maybe whatever is getting stuck or tripping your computer will dissolve and burn away.

SFP

First off on an OBDI cars all this will do is put money in the parts store’s pocket. OBDI monitors sensors for open/short circuit, not reading out of range. Also on OBDI cars, there is no on board protocol to turn off the CEL, it has to be canceled manually. This is one big advantage of OBDII.

@fandango

A better question is why can’t they just have a digital LED readout of the code on a car? It’s 2008 for crying out loud. My car has three on-board computers and the best they can do when there is a problem is turn a light on? Then I have to chug down to the autozone and beg the dullard behind the counter to check it out. I know the computer just reports a code, and doesn’t actually always state the problem, but it’s technically feasible to display the code, so why don’t they do it?

Three computers? It is to laugh. Try twenty to twenty five. On a current production car there may be as many as 200-300 codes that can trip a check engine light. Then on top of that, you have permanent/intermittent status, counters, frozen values, and a bunch of other data that there is no way in hell you could get out of a on board display in any type of usable form.

[LSLGuy]

Also, some people are confusing “check engine” with “service engine soon”. Two totally different functions.

The “check engine” is mandated by the Feds, and as amply explained by the experts, monitors emissions-related issues. As low as emissions from a healthy engine are now, that really converts to “monitors everything about engine & exhaust system operation.”

“Service soon” is a mileage-based based reminder. Essentially, it puts the service schedule from the owner’s manual into the computer. So if the manual says you should change oil every 3000 miles, then every 3000 miles the light will come on, and remain on until reseet by some arcane semi-secret switch flipping as noted above.

Some “service soon” systems are smarter than just pure mileage, incorporating harshness of use, or temperature or … Some can remind for oil changes, various levels of preventative maintenance checkups, transmission flushes, etc. Others are just 3000 = light on.