Service Engine Soon Light On?

Reader Question:

Hello Austin, I recently had the “service engine soon” or “check engine soon” light come on in my Buick. Took it to my mechanic, and he said it was the EGR valve which he changed out for over $500. The light came on again within 24 hours and I took it back. He said he tightened the fittings, and said that the EGR computer may need to be replaced!??? Since then the “service engine light” has gone off and come back on several times. What is going on?

Thanks Leo

Thanks for your question Leo. I think you should ask for your money back on this repair. The on-board computer system in your older Buick is fairly rudimentary compared to newer models and does not give the most in depth diagnostic information. The EGR valve is fairly expensive for your Buick, and the price sounds ok. However, if the problem is still not resolved you should ask to have your old valve re-installed. (You did ask to keep your old parts and their original boxes didn’t you? If not, this might end up being an expensive lesson for you, but one you probably will remember for the next repair.)

Tightening the fittings is a cop out, and is probably his way of saying “I don’t know how to fix it.” The Service Engine Soon (SES) light can be very tricky to turn off sometimes…it is best to diagnose the problem when the light is on. Every time you turn off the car and re-start the engine, the on-board computer does a sequential self check of all the sensors and components on the car. If the car has not been driven far or long enough, the system will not be able to complete its test. These shorter drives is one of the reasons why the Check Engine Light won’t always come on. So as you drive, the light might come on and stay on as the computer finds a fault during its routine check list. Also, the faulty component might only malfunction at a certain speed or temperature which is VERY common.

My guess is that the EGR valve is NOT the problem, but your mechanic received an EGR trouble code from your computer system while running a diagnostic test. There are more components of the EGR (Exhaust gas Re-circulation) system than the valve, and any of those can cause an EGR trouble code. Something in the EGR system isn’t working properly, and the fix isn’t going to be tightening the fittings.

If you can’t get your money back, have him try his second diagnosis – a new computer (There is no such thing as an “EGR computer” on this car) at HIS expense to see if the problem goes away. My intuition tells me that this mechanic may not be very computer-savvy, and if so, he may just be over his head. The computer very rarely requires replacement. Just like your PC at home, where most malfunctions are software related, we just don’t need to replace car computers very often. If he really thinks this is the problem, he can locate an after-market computer for this car at around $100 and install it easily. He won’t be out-of-pocket near as much as he asked you to invest in his misdiagnosis the first go round.

If you are an established customer at his shop, your mechanic will want to fix this misdiagnosis problem and maintain a good relationship with a good customer..

Here is an example of the procedure I would expect a mechanic to follow when diagnosing this SES light:

1. Read and record the computer system trouble codes the customer is experiencing.
2. Reset the computer and test-drive the car at freeway speeds to verify that the code re-appears (your car is capable of correcting some problems itself, and we don’t want to dig into your car and wallet before first verifying that there really is a malfunction requiring intervention). If the code doesn’t reappear after testing the car, return the car to the customer. If light comes on again, bring car in as soon as possible, preferably before turning it off again.
3. If a code does appear, test all components represented by that code. For a suspected faulty EGR valve, replace it with a new one. Either keep the original part in the EGR valve box labeled with customer name for 30 days or give the original part to the customer to hold onto.
4. If the SES light comes on again, re-read the computer codes to verify it is the same problem. If it is, scratch head and then keep inspecting and possibly replacing other components of this system (i.e.,  inspection of EGR vacuum lines) until the problem is located and the check engine light is out.
5. Once light goes out and stays out, re-install the customer’s origianl EGR valve that evidently wasn’t broken and give the customer a credit for this part.
6. Invoice the customer for ALL of our time involved in diagnosing and repairing car, but only for parts that were used.
7. Return all parts ordered but not permanently installed on car to the vendor for credit.

Like ours, many established shops keep an inventory of old parts to use as test parts in cases like this. Any time your mechanic isn’t one hundred percent sure of a fix, ask him if he can try a good used part before ordering a new one, especially if it is a pricey component.

Even the best mechanics frequently have to guess and fix some problems by trial-and-error. so be patient. This type of problem can be tough to diagnose and repair even for the most trained mechanic with the best diagnostic equipment.

Before I go, let’s make sure that you are familiar with the dash light warning system.

A Yellow Warning light, like the Check Engine Light or Service Engine Soon Light, tells you that the computer’s sensors have detected an issue that needs attention. It is not necessarily urgent, but should be checked out by your mechanic at your convenience in the next week or two.

A Red Warning light is telling you to pull over and turn off the car NOW. Your car has a serious problem that requires immediate response from you. It’s a shame, but in my experience, the damage is often already done by the time the red light comes on and the customer can safely navigate off the road and turn off the car.  Time really is critical here, so if you ever see a red engine light, get that car stopped IMMEDIATELY.

Hope I have been able to help you think through your problem and head toward a solution.

Blessings,
Austin Davis