Calling All Car People: Service Engine Soon Light Is On - Serious?

Factual Questions
1

I have a 95 Saturn (56,000 miles) I use only to drive to work.
Starting four days ago, the SERVICE ENGINE SOON light comes on.

The light only comes on after I start the car and drive about 3 miles. I can stop, turn off the engine and the light immediately goes off and won’t come back on until I drive about 3 miles again.

I’ve checked spark plugs, coolant, and oil. All is ok.
The engine sounds good as new…no knocks, no funny noises whatsoever.
From cruising the internet, I see the problem is often not with the engine, but with the sensor to the SERVICE ENGINE SOON light.
I really do not want to take it to the Saturn dealer (I have bad luck with dealerships…) unless it is really necessary.
My questions are:
Can I do anything else to find out why the light is on?
If I ignore the light - will it ever just go away, or is that a bad thing?

2

free trouble code reading at pepboys

if you live in an area where you have to get an emmisions check every year bring it in soon as you might damage part of your emmision control. Otherwise you can wait a little longer.

Just my humble O

3

FREE at Pepboys…I like that!
Thanks a lot, k2dave!

4

You could always do what Max Carnage did with his Saturn. Battery ran down, put in new battery, no more Service Engine light. Ta-da. :slight_smile:

On my Olds, it was a plug that had come loose from the air conditioner. Five minutes at the dealer.

5

There can always be exceptions, but as a general rule if the car is running well the “Service engine soon” light doesn’t indicate an urgent problem. However, there’s no way to know whether it’s a potentially serious problem without reading the trouble code memory and having some understanding of the system.

There are dozens of circuits related to drivability that are monitored by the electronic control unit (ECU, commonly called the computer). Various out-of-range values in any of these circuits can cause the light to come on and set a trouble code in the ECU’s memory. Some of these could cause trouble if ignored, others probably won’t.

A good auto service facility can access the trouble code memory and advise you what needs to be done, if anything. It generally doesn’t cost a lot to get that far. If there’s an indication of a problem that should be investigated and/or corrected, there will be further expense.

There are parts stores that offer free trouble code reading, usually in the hope of selling a part (that may or may not solve the problem). But generally they don’t really understand the systems, and their advice is not necessarily well-informed. As in most areas of life, you usually get what you pay for.

6

On the older GMs, all you needed to retrieve the trouble codes was a paper clip, and a sheet of paper to tell you what each code means. You’ll find information on how to do this at www.thirdgen.org, but I think your car uses the newer, OBD-II (On Board Diagnostics) system, for which the paper clip trick won’t work.

If Pep Boys is unable to retrieve the code for free, they do sell an assortment of tools to do so—not nearly as informative as the diagnostic tools the dealer has, but it’s a good start.

There are plenty of good independent mechanics who can service modern computerized cars—I’m sure Gary T will pop in here to tell you how to choose one. They may or may not be less expensive than the dealer.

The car’s “computer” might go by several different names, such as ECM (Electronic Control Module) or PCM (Powertrain Control Module.) In any event, there is a multitude of things the computer is “watching,” and when it sees something fall out of spec, it stores a code in memory, and triggers the Service Engine Soon light.

Depending on the system your car has, disconnecting the battery for a few minutes might erase the trouble code, thus turning off the light. But that would only serve to disguise the problem, not fix it. Also, it’s very hard for the mechanic to investiage your complaint if the trouble code has been erased.

When the computer detects a faulty sensor, it will substitute with a fixed value----an educated guess, if you will----and the engine will run okay until you can get it fixed. But don’t wait forever to do it.

By the way, as far as all those dashboard warning lights, think of them in three colors, like traffic lights: Green (turn signals, automatic load-leveling)= go. Yellow (low fuel, check engine)= take it easy; take care of the problem as soon as possible. Red (oil, alternator, temperature) = stop immediately.

7

Unfortunatley, the service engine soon light can be misleading. My parents had an 87 Buick LeSabre whose light was on constantley for no reason. Same with a friends 94 Explorer. However, when the light came on my 87 Grand-Am it indicated a thrown rod ie, my engine was totalled. I would NOT ignore that light, get it checked out IMMEDIATLEY !

Good luck.

8

For other readers who are pondering their own Check-Engine light while nibbling their cuticles and fretting, Here’s a rule of thumb for cars made more recently: if a warning light is RED, it means get the thing checked ASAP and you should probably stop driving the car. If a warning light is orange (and check engine lights generally are) it means the car can be safely driven, under normal conditions, until you can get the thing checked out.

I drive a Honda and the check engine light on my car usually means I didn’t crank the gas cap hard enough–talk about a non-problem. But you can’t tell without getting it checked it out.

9

correction It’s at Autozone.

10

CHECK THE MANUAL

I was once driving to a client with a few coworkers. I was in the front passenger seat. Twenty miles from the home office – and two hundred to go – the SERVICE ENGINE SOON light came on.

“EEEK”, screamed the driver, “Does anyone know what that means?” No one had any suggestions, so I reached into the glove compartment and read the manual. It said something like, “This light will come on at 60,000 miles to remind you to bring the car in for servicing. It can be turned off only by an authorized dealership.”

So I asked the driver what the odometer said. “It says we’re at 60,003 miles, why?”

Emergency over.

11

Were it not a big deal, it would say, “Check engine when you can get around to it.” Is it worth the gamble of potential engine destruction NOT to get it checked?

12

Well, I don’t follow that logic. It’d make for a crowded dashboard to have things like “The Car is not going to run if you don’t get gas NOW” written where the “E” is, and the brake light would be hard to read if it said “BRAKES ARE GOING TO FAIL SOON! AIIIIIIIIEEEEE!” and so on.

I think that’s why the color-coding makes so much sense. At the very least, you know whether to pull over and lunge for the manual immediately, or whether to wait until you get home to look it up.

13

You might try looking at your display by where the light comes on to see if there is a place to put a key in. My girlfriend’s car had a Service Engine Soon light that would come on after so many miles, but it could be reset by putting the car key in a slot on the dash and turning it. It’s a long shot and probably not the best thing for the car, but if you really want the light off it’s worth a check…