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Re: '03 LeSabre 3.8 Check Engine Light Flashing

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Jun 27, 2021, 9:58 PM

Post #1 of 4 (271 views)
Re: '03 LeSabre 3.8 Check Engine Light Flashing Sign In

I am having a similar issue, initially I had a evap code on my car. I got a gas cap for my car hoping that might fix it. I erased the codes, the code came back on after a couple days so I assumed it was the same code. Two months later while trying to diagnose the running problem in my car I decided to check the codes again on the car. The evap code was nowhere to be found, however it gave me a p0306 code. Upon researching I found that the spark plugs might be the first cause. Even though they had been fixed about a year ago I decided to get new plugs and wires. After installing the new plugs and wires, I noticed that the car is still running a code, and running poorly. The new code however is a p0300 code. The lights are also flashing engine lights, back to steady, also for the first 20 minutes of driving there is no code on the car whatsoever. The car runs fine for about 20 minutes and then starts flashing engine light codes, followed by a steady engine light code. I have determined that it is either likely one of my fuel injectors, or maybe the intake gasket. I can hear a vacuum leak, or what sounds to be vacuum leak since I have bought the car and have always had the issue with this car running rough at idle after warming up. It will run fine for about 20 minutes, but after the car warms up it starts misfiring. I have sprayed all the vacuum lines and the intake gasket, and can find no verifiable vacuum leaks, even though it seems obvious that I can hear one. I am posting in hopes that someone might have some other advice. I have gotten new injectors that I plan to install on Tuesday. Any advice would be helpful?
My car is a 2003 Buick LeSabre 3.8 engine. The intake manifold also has been replaced in 2020 just before I bought this car, and I would presume it should not need to be fixed again.

(This post was edited by Tom Greenleaf on Jun 27, 2021, 10:21 PM)

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jun 28, 2021, 3:28 AM

Post #2 of 4 (253 views)
Re: '03 LeSabre 3.8 Check Engine Light Flashing Sign In

The P0306 indicates a misfire on cylinder #6. The P0300 indicates multiple, random misfires through multiple cylinders.

The flashing of the light is a feature to warn you that you have a misfire serious enough to damage a Catalytic Converter and you should stop driving it immediately until it is fixed.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.


Jun 30, 2021, 9:32 PM

Post #3 of 4 (212 views)
Re: '03 LeSabre 3.8 Check Engine Light Flashing Sign In

If the LeSabre was my car, my first step is removing the spark plugs to check if one or more have oil at their bottom. Do not worry much about oil on the top part of the spark plug, at least not in this case. If oil is present on the top part of the spark plugs, it means the replacing of the upper manifold gasket was done improperly. But such is not the cause of misfiring.

Do not hurry in installing the new injectors yet, and try to check first if they work properly. You just need a cheap multimeter from Harbor Freight and watch a YouTube video showing how to do it. To remove the injectors connectors, you press the metal holding wire and pull it, very easy on the front side, a kind of hard on the back because wires are running in that area.

If the injectors are fine, you are correct when you think there must be a vacuum leak, there are also videos about checking for leaks without spending much money. These cars. all of them, sound like having a leak somewhere, I used an ultrasonic diagnostic tool in one of them and never found the "leak" location.

Also, with tools that cost about ten bucks each, you can check the spark plugs and the Ignition Control Module. The tools are the Ignition Spark Tester, and a Circuit Tester. Also and again, write in the YouTube search engine bar: Ignition Spark tester and you can learn easy how to test the spark plugs. Same with the 3.8 Buick engine Ignition control Module.

By the description given by you, I might ask if your car is losing more oil than usual, like if you must need to ad more oil every 1,000 miles or so.

Lets play with possibilities,

1)- One or more spark plugs are faulty, then replace them
2)- One or more injectors are faulty, then replace them.
3)- There is a vacuum leak, then replace tubes or sealers.
4)- One or more Ignition Control Module are not working, then replace it. This module cost more than 100 bucks new AC Delco and you can find used for 30 bucks on eBay. When installing it use a little bit of thermo grease at the bottom of it. Don't use regular grease.

Deleted incorrect advice

The Buick LeSabre is a lovable vehicle, I like how it runs, is quite and soft on the streets, very comfortable car, specially for long trips. I would spend no more than $200 in diagnosing and repair this car, because is dying slowly not because the amount of miles but because the amount of years.

(I'm not a professional mechanic, but I have had a similar scenario with a 1998 Buick LeSabre. The car still is running fine after the replacing of the Ignition Control Module and the "treatment" with the cheap repair product.)

My regards.

(This post was edited by Hammer Time on Jul 1, 2021, 3:31 AM)

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jun 30, 2021, 10:42 PM

Post #4 of 4 (210 views)
Re: '03 LeSabre 3.8 Check Engine Light Flashing Sign In

Quote from top post >"I can hear a vacuum leak, or what sounds to be vacuum leak since I have bought the car and have always had the issue with this car running rough at idle after warming up.<"
Luchito - appreciate the list of items but let's find out where that vacuum leak or what sounds like one is before tossing this engine on your list!
Smoke machines, assorted sprays at target areas in this case all involved with a recent intake manifold job - things break or left removed by mistake.
It CAN run well for a warm up time so let it be found BEFORE it wrecks converter if not too late now.
Seems to me it is a vacuum leak a cold engine (despite warmer weather of Summer) even 100F is cold to an engine. A vacuum leak will confuse all other controls of how to deliver spark and fuel seems to put up with it during that time.
Let's hear back from original poster on THIS SPECIFIC CAR not millions of others with the same model name - OK?


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