What happens if your check engine light comes on, you diagnose the problem, replace the faulty part, but do not clear the check engine code? Is it possible that the light will randomly come on again even though the repair is completed?
After repair, what if you don't clear the code?
- Thread starter Mark72
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Many manufacturers program the ECU so that if the conditions triggering the CEL disappear after 10-20 start/run cycles, then the code will disappear.
Random lights shouldn't appear without the stimulus that is programmed to trigger the light. A random CEL should mean that the problem isn't solved.
Random lights shouldn't appear without the stimulus that is programmed to trigger the light. A random CEL should mean that the problem isn't solved.
If you fixed the problem(s), the code will eventually clear itself.
The computer has different criteria for different ailments but, the most obstinate ones would require maybe ten complete warmup cycles from closed to open loop with no issues.
The computer has different criteria for different ailments but, the most obstinate ones would require maybe ten complete warmup cycles from closed to open loop with no issues.
JHZR2
Staff member
It should clear, but depending upon the computer it could take a long number of drive cycles to be truly ready, and/or it may keep the info in some sort of history longer.
Ok, well I had a computer diagnostic done and it indicated specifically the 3rd bank of the EGR valve as being bad. so I purchased a brand new one and installed it. I kept driving the car and after crusing on the interstate one night about 4 days after I replaced it the check engine light popped back on for about 5 mintues and did it again the next day...but only did it while at highway speeds and engine was good and hot. Yesterday I had my mechancie run a diagnostic again and it read the 3rd bank of the EGR valve again so he cleared it, told me to drive it a while and see. I took it out last night and it did not come back on, but I know it can go a few days without it happening. You think by him clearing it I should be fine now?
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Should be unless the valve is still bad.
gathermewool
Site Donor 2023
Originally Posted By: Mark72
Ok, well I had a computer diagnostic done and it indicated specifically the 3rd bank of the EGR valve as being bad. so I purchased a brand new one and installed it. I kept driving the car and after crusing on the interstate one night about 4 days after I replaced it the check engine light popped back on for about 5 mintues and did it again the next day...but only did it while at highway speeds and engine was good and hot. Yesterday I had my mechancie run a diagnostic again and it read the 3rd bank of the EGR valve again so he cleared it, told me to drive it a while and see. I took it out last night and it did not come back on, but I know it can go a few days without it happening. You think by him clearing it I should be fine now?
No.
Ok, well I had a computer diagnostic done and it indicated specifically the 3rd bank of the EGR valve as being bad. so I purchased a brand new one and installed it. I kept driving the car and after crusing on the interstate one night about 4 days after I replaced it the check engine light popped back on for about 5 mintues and did it again the next day...but only did it while at highway speeds and engine was good and hot. Yesterday I had my mechancie run a diagnostic again and it read the 3rd bank of the EGR valve again so he cleared it, told me to drive it a while and see. I took it out last night and it did not come back on, but I know it can go a few days without it happening. You think by him clearing it I should be fine now?
No.
Well, ok then..that was simple and to the point
LOL. One of you stated it should clear on it's own after a few drive cycles to clear, so....if that is true and it would go away on it's own...whey then would it not go away after my mechanic cleared the code?
It should still be read by emissions testing guys.
Even thought it may not appear on the dash, it is a 'hidden' code.
So get it cleared, if you can, and get a fresh start.
Even thought it may not appear on the dash, it is a 'hidden' code.
So get it cleared, if you can, and get a fresh start.
Originally Posted By: Mark72
Well, ok then..that was simple and to the point
LOL. One of you stated it should clear on it's own after a few drive cycles to clear, so....if that is true and it would go away on it's own...whey then would it not go away after my mechanic cleared the code?
The only reason the malfunction indicator light would eliminate is because a current fault is detected, clearing the code or a code in memory has nothing to do with it. The fault is current if the light comes on.
Well, ok then..that was simple and to the point
The only reason the malfunction indicator light would eliminate is because a current fault is detected, clearing the code or a code in memory has nothing to do with it. The fault is current if the light comes on.
You know what Vikas...As I'm well aware of your smart a @ @ coment in my other thread in regard to this same issue it really goes to show your maturity level. Don't question what someone says until you know the facts. So go look up the various types of EGR valves that GM has installed on the Chevy Luiminas before you come on here with ridiculous comments that do nothing to furhter the cause of this entire forum.
Originally Posted By: Mark72
the 3rd bank of the EGR valve as being bad.
the 3rd bank of the EGR valve as being bad.
gathermewool
Site Donor 2023
Sorry for being so short in my previous post; I had to run at the last minute. Sorry if it came across wrongly.
When the code was reset, it was really the readiness status that was reset. Regardless of whether the fault-causing issue was resolved, your ECU (the brains) will have to cycle through that specific check a number of times before it will determine whether, the fault still exists. If the fault does still exist, the check engine light will reenergize and the code will be stored in memory. If the fault is not present, the check engine light will remain off.
I had an issue with my EGR system on my '97 Subaru a couple of years back. The code was for EGR Flow Malfunction. It must be the EGR valve, right? Wrong! Even though the Subaru dealership said this was the cause and quoted me for a new one, the Check Engine Light only came on every few weeks, so I decided to hold off and do some research. What I found was that, at least for Subarus, this is a major pain to fix.
Fast forward a year and my CEL was on continuously with the same fault code. I had already cleaned the soot and buildup from the valve itself and tubing. I had already changed all of the vacuum hoses. I had already verified that the valve worked properly - for this model Subaru, the valve can be raised with a finger, which will cause the engine to nearly die. I had already verified that the valve opened when the engine was revved quickly.
I was literally days away from needing to take my car in for emissions when I checked all of my notes again. Luckily, one thing stood out like a sore thumb and I cross my fingers as I rechecked it. When the engine is cold, the EGR vacuum solenoid (the thing that ports vacuum to the top of the EGR valve to open it) should remain closed to keep the EGR valve closed. All of my previous checks to verify that the EGR valve opened when I revved the engine were while the engine was warm. As soon as I started my car the next morning I gave a gentle rev and the valve opened just as it had while warm! I was so excited that I said to heck with finding a junkyard part and paid the $70 to the dealer for a new vacuum solenoid after verifying that I could NOT, in fact, blow through the new solenoid. The old one was stuck open and could not be cleaned, finagled or mechanically agitated to make it shut again.
The points of my story are these:
1. Clearing the fault code by resetting the ECU does not ensure the fault-causing problem has been solved.
2. If the problem is back, but sporadic now, then the valve may have needed a cleaning, but was not the sole issue.
3. Do some research. Throwing parts at a problem may end up costing a lot of money, and still not fix the problem.
When the code was reset, it was really the readiness status that was reset. Regardless of whether the fault-causing issue was resolved, your ECU (the brains) will have to cycle through that specific check a number of times before it will determine whether, the fault still exists. If the fault does still exist, the check engine light will reenergize and the code will be stored in memory. If the fault is not present, the check engine light will remain off.
I had an issue with my EGR system on my '97 Subaru a couple of years back. The code was for EGR Flow Malfunction. It must be the EGR valve, right? Wrong! Even though the Subaru dealership said this was the cause and quoted me for a new one, the Check Engine Light only came on every few weeks, so I decided to hold off and do some research. What I found was that, at least for Subarus, this is a major pain to fix.
Fast forward a year and my CEL was on continuously with the same fault code. I had already cleaned the soot and buildup from the valve itself and tubing. I had already changed all of the vacuum hoses. I had already verified that the valve worked properly - for this model Subaru, the valve can be raised with a finger, which will cause the engine to nearly die. I had already verified that the valve opened when the engine was revved quickly.
I was literally days away from needing to take my car in for emissions when I checked all of my notes again. Luckily, one thing stood out like a sore thumb and I cross my fingers as I rechecked it. When the engine is cold, the EGR vacuum solenoid (the thing that ports vacuum to the top of the EGR valve to open it) should remain closed to keep the EGR valve closed. All of my previous checks to verify that the EGR valve opened when I revved the engine were while the engine was warm. As soon as I started my car the next morning I gave a gentle rev and the valve opened just as it had while warm! I was so excited that I said to heck with finding a junkyard part and paid the $70 to the dealer for a new vacuum solenoid after verifying that I could NOT, in fact, blow through the new solenoid. The old one was stuck open and could not be cleaned, finagled or mechanically agitated to make it shut again.
The points of my story are these:
1. Clearing the fault code by resetting the ECU does not ensure the fault-causing problem has been solved.
2. If the problem is back, but sporadic now, then the valve may have needed a cleaning, but was not the sole issue.
3. Do some research. Throwing parts at a problem may end up costing a lot of money, and still not fix the problem.
I had a 1992 S10 that was throwing the EGR code off and on for over a year. I replaced the valve, but that check engine light didn't go away.
It turned out the EGR passages were full of carbon.
It turned out the EGR passages were full of carbon.
Originally Posted By: Mark72
Ok, well I had a computer diagnostic done and it indicated specifically the 3rd bank of the EGR valve as being bad. so I purchased a brand new one and installed it. I kept driving the car and after crusing on the interstate one night about 4 days after I replaced it the check engine light popped back on for about 5 mintues and did it again the next day...but only did it while at highway speeds and engine was good and hot. Yesterday I had my mechancie run a diagnostic again and it read the 3rd bank of the EGR valve again so he cleared it, told me to drive it a while and see. I took it out last night and it did not come back on, but I know it can go a few days without it happening. You think by him clearing it I should be fine now?
What is really going on with your car is that when the third part of your valve is openning the pressure change in the manifold doesn't change enough so it thinks the valve must not be opennning or the port is clogged. Your problem is the fairly easy to clean port is not clean enough or is mostly plugged up. Get a real good flashlight take off the valve and the hose going to the t body and look through the t body and you will probably see a large blob of carbon where it dumps egr in to the intake. That stuff needs to be cleaned out with carb clreaner and picks or screwdrivers are whatever you can run through the passage. I also run the old speedo cable in the drill through the port also.
Ok, well I had a computer diagnostic done and it indicated specifically the 3rd bank of the EGR valve as being bad. so I purchased a brand new one and installed it. I kept driving the car and after crusing on the interstate one night about 4 days after I replaced it the check engine light popped back on for about 5 mintues and did it again the next day...but only did it while at highway speeds and engine was good and hot. Yesterday I had my mechancie run a diagnostic again and it read the 3rd bank of the EGR valve again so he cleared it, told me to drive it a while and see. I took it out last night and it did not come back on, but I know it can go a few days without it happening. You think by him clearing it I should be fine now?
What is really going on with your car is that when the third part of your valve is openning the pressure change in the manifold doesn't change enough so it thinks the valve must not be opennning or the port is clogged. Your problem is the fairly easy to clean port is not clean enough or is mostly plugged up. Get a real good flashlight take off the valve and the hose going to the t body and look through the t body and you will probably see a large blob of carbon where it dumps egr in to the intake. That stuff needs to be cleaned out with carb clreaner and picks or screwdrivers are whatever you can run through the passage. I also run the old speedo cable in the drill through the port also.
I agree on the port plugged theory.
My GM service manuals say the car is really rooting for you, and if it checks "X" once per drive cycle as part of the I/M readiness, it will check a broken part several times, hoping to find it fixed.
Sometimes there's a counter, so it has to pass (or fail!) so many times in a row. If you clear the code, you clear the I/M stuff, so it has to start over.
My GM service manuals say the car is really rooting for you, and if it checks "X" once per drive cycle as part of the I/M readiness, it will check a broken part several times, hoping to find it fixed.
Sometimes there's a counter, so it has to pass (or fail!) so many times in a row. If you clear the code, you clear the I/M stuff, so it has to start over.
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