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OBD2 scan reveals unexpected engine problems?

Tiny
ALPHAA10
  • MEMBER
  • 1998 BUICK LESABRE
  • 3.8L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 252,000 MILES
Yesterday, I requested an OBD2 system scan at two local auto parts stores. Just a routine check-- it doesn't hurt to be watchful.

Both scans agreed my engine had two issues--

Scan Issue 1--
Error P0304-- misfire on cylinder 4. In checking this error with my local auto parts store, I was offered a single spark plug for a replacement, but since the old rule is to replace all plugs at the same time, do you recommend I replace all six plugs? (Of course, I can diagnose with only a single plug to determine whether it makes a difference.)

Scan Issue 2--
Error P0404-- EGR open position performance
Error P1404-- EGR closed position performance
On these errors, I was puzzled, since the EGR valve is indicated both stuck open and stuck closed, Possibly, the valve is so dirty, it will wander slowly between open and closed. A new replacement valve is somewhat expensive, so I would prefer to take the valve assembly apart, and clean it like a dirty carburetor, with carb cleaner spray and small, stiff brush. Will that work? Do you recommend an overnight "soak" in cleaner, and if so, what cleaner?
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Thursday, February 1st, 2024 AT 8:23 PM

19 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,940 POSTS
Yes, I would change all of the spark plugs and wires at once. Also, on the EGR I would try cleaning it like you have suggested and if that doesn't work replace the valve.

Here is a guide to help walk you through doing the spark plugs:

https://www.2carpros.com/articles/how-to-change-spark-plugs

AC Type .................... 41-921

here is the location of the EGR and I can tell you with this type of valve you will probably end up replacing it, but you never know. Check out the images (below). Please let us know what happens.
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Friday, February 2nd, 2024 AT 9:35 AM
Tiny
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Ken, thanks for your response. In researching the problem, I found several additional parts to the EGR valve-- presumably bought separately.

(1) EGR solenoid
(2) EGR sensor

This information comes from a phone chat with an auto parts rep, so I am not sure how much is accurate. In general, should I look further into these items? Ordering them locally may be more difficult, but Rock Auto may stock them.
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Friday, February 2nd, 2024 AT 7:49 PM
Tiny
KEN L
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I like Rock Auto; I would get the parts from them. I am not sure about buying the EGR parts separately, I think it is all inclusive. It will show an image on rockauto to confirm.
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Saturday, February 3rd, 2024 AT 10:00 AM
Tiny
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  • 170 POSTS
How much of a hazard is posed by driving the car for a few days' of local trips with the old (and suspected defective) EGR valve still in place, pending arrival and installation of the new EGR valve?

The P0404 and P1404 codes appeared when I asked my local O'Reilly's to scan the system for errors, if any. Unfortunately, I had not done regular scans before that date, so the first (but unnoticed) code appearance can be only guessed to have been two months ago.

Although I would like to clean the original EGR valve, and actually loosened the valve to invert it for overnight "soaking" in brake cleaner spray, the next step is to pry the silver EGR mating gasket loose from the throttle body. If that gasket breaks or crumbles, that makes the situation worse, since I cannot use the original but broken gasket.
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Thursday, February 15th, 2024 AT 3:19 PM
Tiny
KEN L
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The EGR valve in place but not working will cause the engine to emit KNOX gases which is not good FYI.
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Friday, February 16th, 2024 AT 10:26 AM
Tiny
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In this car engine, the EGR valve appears stuck closed-- when I start and run the engine to warm up, exhaust smell enters the cabin. Trying to understand the EGR system, the oxygen sensor tells the BCM computer the engine is ready to receive partially-burned exhaust gases, and the computer diverts some of the gases into the EGR. Which is stuck in the closed position, despite the computer's order to open for exhaust gases. That closed position explains the exhaust smell, but doesn't it also introduce the possibility the computer has switched to a leaner mixture, to accommodate the exhaust gas it "believes" are being diverted into the cylinders? And that means my stuck EGR is actually running my engine hotter and leaner. What damage could this introduce?
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Saturday, February 17th, 2024 AT 2:15 AM
Tiny
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More information.
This afternoon, I attempted to remove, disassemble and scrub-clean the EGR, hoping clogged passages are the only problem. Unfortunately, I could not devise a way to take apart the EGR for a more thorough cleaning than simply squirting throttle body cleaner into both passages. Is it possible to disassemble an EGR for this GM engine? I found one TORX-type screw on the bottom-center, which seemed to be spring-loaded, but which simply rotated, and did not unscrew. And where two bolts appeared to pass through the EGR body, there was no visible opening for a nut or bolt head on either side of the body.
This EGR is the electronic type, with only a five-pin connector inserted into its top portion, and no other lines or connectors.

Here is a multi-view graphic for the part:

https://www.rockauto.com/en/moreinfo.php?pk=6698424&cc=1303287&pt=4968&jsn=9

.
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Saturday, February 17th, 2024 AT 3:23 PM
Tiny
ALPHAA10
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For better or worse, I have decided to do what most people do-- buy a new EGR valve. There are too many factors to control, especially since the car has an undocumented history, to spend more time experimenting with a used, questionable valve.

Thanks for the discussion of options !
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Sunday, February 18th, 2024 AT 12:28 AM
Tiny
KEN L
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You are welcome, please use 2CarPros anytime we are here to help.
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Monday, February 19th, 2024 AT 8:38 AM
Tiny
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Ken, in attempting to understand more of the EGR system, does this explanation of my EGR symptoms make sense?

In this car engine, the oxygen sensor tells the PCM computer the engine is ready to receive partially burned exhaust gases, and the computer diverts some of the gases toward the EGR. The EGR, however, seems stuck in its closed position, despite the computer's order to open for exhaust gases. That closed position explains an exhaust smell in the cabin, but it also means the computer has switched to a leaner mixture, to accommodate the exhaust gas volume it "believes" is being diverted into the cylinders.
And that means my stuck EGR is actually running my engine hotter and leaner.
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Monday, February 19th, 2024 AT 8:41 PM
Tiny
KEN L
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Nothing explains "an exhaust smell in the cabin". There should be no smell in the cabin. Here is an explanation I found that tells you what the EGR does:

The Exhaust Gas Recirculation (EGR) valve is a component used in automotive engines designed to reduce nitrogen oxide (NOx) emissions, which contribute to air pollution and smog. The EGR valve works by recirculating a portion of the engine's exhaust gas back to the engine cylinders.

Here's how it functions:

Reduces Combustion Temperature: By reintroducing exhaust gases into the combustion chamber, the overall temperature of the combustion process is lowered. High combustion temperatures are a primary cause of NOx formation. By reducing these temperatures, the EGR valve helps in reducing the levels of NOx produced.

Improves Efficiency: Although the main purpose of the EGR valve is to reduce emissions, in some engine designs, the recirculation of exhaust gases can also lead to a more complete burning of the fuel, which can improve engine efficiency and fuel economy.

Emission Control: The EGR valve plays a crucial role in helping vehicles meet emission standards set by various environmental agencies. By controlling the amount of exhaust that is recirculated, the valve helps manage the engine's emission output.

The EGR valve can be operated differently depending on the engine's design and the vehicle's driving conditions. It might not operate at cold start or at full throttle; instead, it is active during cruising or light throttle conditions, where the engine's efficiency is optimized, and emission control is most necessary. Over time, EGR valves can become clogged with carbon deposits, which can lead to performance issues, and may require cleaning or replacement.
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Tuesday, February 20th, 2024 AT 11:07 AM
Tiny
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This afternoon, I got the EGR, and plan to install it tomorrow.
Need your opinion on whether to use the stamped metal gasket which came with the part, or use an exact-fit, layered asbestos fabric (?) Gasket for the same part, which I ordered separately, in case the EGR did not come with a gasket. The layered, fabric gasket is the more conventional kind of gasket, and may provide a better seal under extreme heat.
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Friday, February 23rd, 2024 AT 3:38 PM
Tiny
KEN L
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The gasket it came with should work just fine.
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Saturday, February 24th, 2024 AT 9:29 AM
Tiny
ALPHAA10
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Ken,
After installation of the EGR, an OBD2 system scan (O'Reilly's) showed no primary diagnostic trouble codes, which is good news..
Now, I am puzzled-- if I have not installed the spark plugs and wires, yet, how could the P0304 code for "misfire on cylinder 4" simply disappear?
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Tuesday, February 27th, 2024 AT 10:19 PM
Tiny
KEN L
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Because if the exhaust gases are leaking from the EGR it can affect individual cylinders.
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Thursday, February 29th, 2024 AT 12:02 PM
Tiny
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If exhaust gases can leak from the EGR, could that explain occasional whiffs of exhaust gas in the cabin, too?

(After EGR replacement, I have not detected any exhaust gas smells-- so far.)
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Thursday, February 29th, 2024 AT 3:37 PM
Tiny
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Ken, now I understand what you meant by "leaking from the EGR". The EGR, itself, does not leak to the outside, but fails properly to open or close on computer signal. That introduces an improper fuel/air volume into the nearest cylinder.
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Thursday, February 29th, 2024 AT 7:19 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,244 POSTS
Hi,

Thank you for the update. Have you been able to resolve the issue? We're interested in knowing.

Take care,

Joe
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Sunday, March 3rd, 2024 AT 9:07 PM
Tiny
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Yes, Joe, I have been able to resolve the codes issue for my Buick 98.

Earlier, I had received two EBD2 warning codes-- P0404 for an EGR
valve "open position performance" and P1404 "closed position
performance" and one EBD2 code P0304 for "cylinder 4 misfire
detected".

After installing a new GM-brand EGR from RockAuto, all codes simply
disappeared, including the P0304 "cylinder 4 misfire" Of course, I have
not operated the car much since the EGR installation, so the "Check
Engine" light might reappear.

My problems with this car arrive dramatically, and more or less
unexpectedly, because the wife of the person who sold the car to me
simply had tossed out all the services documentation over the years,
so, I have to guess what items will malfunction next.

The car has 252k miles, but was well-maintained by a professional
shop, so that offers some relief.

The car was received without the passenger side wheel well inner
sleeve, which protects the accessory belt and pulleys from splashed
water and road debris. I know the number of the OEM part for the
sleeve, but no one' has it. (I have not searched all the junkyards.)
To resolve that problem at least, for now I am searching for a
robust, waterproof material to use for a hand-made sleeve.

Any ideas?
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Tuesday, March 5th, 2024 AT 3:10 AM

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