Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Service engine soon sign

The service engine soon sign came on awhile ago. I immediately took it to a garage and they said they can’t find a code. My mechanic friend checked it and found a lean combustion condition. What could be causing this issue and what can I do about it. This yellow service engine soon light is driving my nuts!!!

Take The Caddy To A Nationally Know Auto Parts Store, Like An Advance Auto Or Autozone.

A friendly counterperson should cheerfully follow you to the parking lot and read those diagnostic trouble codes for you (1996 and newer cars), using a code reader. Be ready to write them down exactly as given . . . PO123, PO454, etcetera, and post them here.

We need some specific codes in order to make some better educated guesses and to offer advice to you.

FYI for about $50 you can buy your own code reader (for cars 1996 and newer), read your own codes, and turn off that light ! I have an Actron Pocket Scan. It works great. Please know that the problem should be found and corrected. Turning out the light doesn’t fix anything.

By the way, what model-year is this Seville ?


This is a 2004 SLS. I will get codes and post for you…thanks

The codes are P0171 and P0174

The cause could be as simple as a partially clogged injector. Someone will need to check it out.

Clean the mass airflow sensor.

Check it for vacuum leaks.

Check the fuel pressure.

(Or have someone do those things).

Hi–Having just been told by our dealer that it’s $50 just to read the code ( !! ) for our Prius, and having heard on Car Talk I could buy one of these (I waited too long), I’d like to try the Actron Pocket Scan. Once you have the code, where do you go to look up its meaning? Obviously, if it’s other than an oil check or a scheduled service visit, I’ll have an expert work on it. The car is still under warranty, which is why I feel I need to go to the dealer.

I have always been fond of this website:

The main list there is for generic OBD II codes. Once you get past P0999 you’re into manufacturer specific codes and your best bet is a manufacturer-specific discussion forum - Toyota in your case.

If you’re not in California, you should also be able to get your codes pulled free at any auto parts chain store.

Excellent. (I’m in VA) Thanks very much.

Was that light a:

  • CEL Check Engine Light: or as you indicated a * SES Service Engine Soon.

I don’t see anything in the original post that indicates a make or model of car. How did CSA know it was a Caddy Seville? Am I doing something wrong?

Old Timer 11, It’s Not You. This Question Was Posted In The Old Format That Had The Make And Model (But No Model Year) . When The “Upgrade” Happened, It Was Lost.

Garden Girl tells us (above post) it’s a 2004 SLS [Cadillac].

She also tells us the DTCs.
“The codes are P0171 and P0174”


Petitefutee, Code Readers, Like The Pocket Scan, Come With A Little Booklet Containing Hundreds Of DTCs (Diagnostic Trouble Codes) And Their Rough Descriptions.

Professional Mechanics and some Shade Tree Mechanics opt for a more expensive code scanner that gives more information right on the unit. Some record real-time data that indicates more about the functioning of the engine and components.

Still, other units can read ABS (anti-lock brakes) and even Body Codes. So, for fifty bucks you can get very basic drivetrain (engine / transmission) codes, but the sky is the limit for purchasing diagnostic devices. Have the friendly folks at the auto parts show the different models.


Thanks CSA, I agree that “upgrade” needs to be in quotation marks.

A lean condition is the result of the problem not the cause. A number of things can fool the computer and cause it to lean out the fuel ratio. A lazy oxygen sensor, mass air flow sensor are a couple I have had. Also other sensors such as the engine temp sensor can also be causing the problem. An Autozone code reading will be pretty much worthless. Someone needs to hook up the $20,000 diagnostic computer so they can read what each of the sensors is telling the computer.


Does this Seville by chance have a light that just warns of an upcoming service (e.g. the SES light), and not throw a code (e.g. the CEL light)? I know at least some Toyotas do that, but I can’t speak for any other makes. If so, there’s normally an easy way to reset it for the next 3K miles (or 5K, or whatever the service interval is).

I know on mine, you simply set the odometer to read odometer (as opposed to one of the trip meters), turn the ignition on while holding the reset button, and it will flash a few times, then go out and it’s reset. No more SES for 5K miles. It’s a reminder feature, nothing more.