I'll zero in on what will help me with this project and using the code scanner to work with the ecm.
Ok first off yes the new codes would show up if
there is any new ones to be recorded:
Just to be sure, are you saying that, yes, even if the ecm is not cleared of the 3 already read codes, that
any new codes would show up during a new read,
along with the 3 codes from the previously read, that have not been cleared from the ecm?
Would a current P0303 code read out from the ecm also, without clearing the P0303 pending code first from the ecm.
Is a pending P0303 ususlly a slight or intermittent misfire?
Is a current P0303 a more regular misfire?
Does a pending misfire change to a current missfire on the ecm even if the level of the misfire stays the same, after a certain amount of driving time?
What does a pending P0303 say about the 3rd cylinder misfire, and how does it compare to a current P0303, as far as being minor, major, spark plug, or fuel injector, etc, as the cause.
As for a misfire affecting the cat it may make it run hot as for it being plugged the only way to really tell is to have a Muffler shop check for exhaust flow:
How long can a cat be run hot before it starts to clog up or not be able to pass it's readiness test?
Is this right? The overly high heat degrades the catalyst, so the unburned fuel or carbon deposits start to clog up the cat.
Will A cat throw a code if it is running hot?
Will A cat throw a code if it starts to degrade?
How many miles of driving with a pending or current single cylinder misfire will start to plug or really plug a cat?
Also you clear the codes so the computer know's that they are gone:
Do you mean after the car is repaired?
IF a code is still there the computer thinks the codes are still problems and runs as such:
Are you saying, that the ecm tries to help the
engines performance by changing settings here and there, etc, etc to compensate for the codes it has picked up?
If yes than wouldn't it be better not to keep clearing the codes if repairs cannot be done right away or soon because the ecm changes settings for better pereformance with the conditions that the codes represent
and/or that the ecm will slow down performance to protect the car with the conditions that the codes represent?
The other reason you should clear them and then drive it till the light comes back on is so that you can see which codes come back so you better diagnos the car to fix it:
I got this part about clearing the codes 1 time so the ecm can check whether any of the codes have gone away even if no repairs were done yet, and that most likely most or all of them would be set again if no repairs are done, unless they were set off by driving way out of the normal type of driving pattern which the ecm is well aware of, which could trigger a code, that would not have been set off during a regular or more normal driving pattern.
Do all engine codes set the engine light? If not, why not?
What kinds of codes set the engine light?
Does it really matter, because it's only telling you that there is an engine code.
As for why the light came on after adding oil makes no sense that should have had nothing to do with it:
This is what happened: I was driving this car after it was running for 5 minutes and and it started to completely misfire and quickly lurch forward running again. It did this pattern a few times in a row and then started running normal again for a few seconds and then did the pattern again and then it started to stay running normal.
Later I checked with the owner, this had never happened before.
I very quickly parked the car and noticed that the check oil light was on. I shut the engine off. I had to add 2 quarts of oil to fill it all the way to max. I did not go over the max line at all.
Later on I read on a Cadilac forum that on that engine it is better to only keep the oil filled up to the top of the fill line and not at the top of the max line.
I told you that the engine light was also on, but now I'm not sure if the engine light was also on at this time.
Because the oil was 2 quarts low, after putting in the Lucas and the 2cnd quart of oil I wanted to be sure that the engine was ok, so I was using the overdrive alot to check for its normal race car like performance. It was all local driving so I had to keep slowing down.
At first the tranny was not shifting smoothly and the car was sluggish or hesitant.
After a while the tranny started to drive normal with full overdrive etc.
After driving around for awhile the tranny was shifting ok and the engine had full power but it wouldn't kick into overdrive.
So I parked the car and the engine was very hot.
The ecm might have been telling the tranny to stop using overdrive?
During this hard run might have been when the engine light was 1st lit and not at the same time that the check oil light was 1st lit.
Later I read on alot of Cadilac forums that this engine does better when it's run hard once in a while or even better if done regularly on a highway or open road, I'm not sure about alot of hard short runs around town with stop signs and traffic lights.
The next day and since then the car runs good and with lots of power. It's down 1 quart of oil just where it's been said it should be kept at.
Less than 1 week later the engine light went off. A few days later I used the scan tool and got the three codes P0100 current, P0101 current, P0303 pending.
Why did the engine light go off if no codes were cleared?
Can the engine light go on without a code being set?
Can a code be set without the engine light going on?
3 weeks later I was zipping around in the car, but not nearly as fast as the
1st run mentioned above and the engine light was on again.
On my next code read there were no new codes, so why would the engine light go on again, without a new code being set?
It's been on since then, and is still on.
I used the scan tool recently and the same 3 codes are there and the P0303 is not showing that it has updated to current.
All of the 8 readiness codes were passed on the code reader on the 1st and 2cnd read.
I've never worked on a late model car before, so the more you can answer from the above the better, before I start taking things apart.
I'll clear the codes and drive it around before I work on the car.
Wednesday, November 19th, 2008 AT 9:26 AM