Check Engine Light
 

I've done a search on the possible causes of a check engine light and have come to the realization that there are many possible reasons. I'm hoping that by describing my situation as detailed as possible there may be some clue as to the reason for the CE light.

My CE light first came on 5 weeks ago. Looked up the posts. Disconnected the battery to reset the CE light. CE light came back on almost immediately. Looked up the posts. Disconnected the EGR tube that runs around the back of the engine. Looked clean and the entry into the engine return looked clear (in reference to the Stevebfl post). Reconnected the tube and the CE light disappeared until today.

Last week Thursday, on the way back from work, the car had some rough idling while I was waiting for the signals. The rough idle disapeared by the time I got home which is 5 miles away. Got out of the car and smelled a strong rotten egg odor. I had not had that type of odor from the car for over 4 years and this time it was VERY strong. Thought the rough idle and odor was from some bad gasoline, the gas level was low. Next trip that evening, no problems: The CE light had not reared its head this entire time, and there was no recurrance of rough idle or odor.

The car takes quite a few short trips (~5 miles). This weekend I ran the car 80 miles round trip at around 80 mph. Filled it with a new tank of gas as it was down to less than one gallon (15.5 gal fillup on 16.4 tank capacity (Not a good idea to run the fuel level this low?) Mileage was the standard 20.5 mpg for the last tank. This afternoon (Monday) on the way to lunch the CE light came on. No recurrence of the idle problems or odor problems since that one trip. Car is running smoothly and well. Any ideas? I will eventually have the codes read. I realize I'm reaching here. Do you think running Techron would help since the car has so many short trips?

Rotten egg odor is indicative of a bad 02 sensor, resulting in the CE light coming on.

GL

Hi 96C280. Don't waste any $$$ until you find out what codes are stored!!! If you can find out, let us know. CHECK ENGINE lights are usually an easy DIY job, but you must know which code(s) are present. Keep us posted.

How do you pull the codes?

OBDII cars can have their codes scanned at most shops. Most dealers have a flat rate charge for pulling codes...

Yesterday, my idle went erratic. The idle at stops would surge and drop almost until it is about to kill the engine (I suppose the surge is to keep the engine running when I think about it now). No check engine light as of this morning, no odor. Idle wasn't very rough this morning but I can still tell it isn't as smooth as before. Power seems a little down. I don't know if there is any correlation, but as I mentioned I drive around town mostly and this past Sunday I had about a 40 mile round trip going up to 90 mph. I had no problems after the trip. Do these blasts on the freeway have after-effects that show up the next day? The last time I had an extended drive on the freeway, I had the rotten egg odor episode, NOT right after the drive, but a day or two later. I will be getting the codes checked today. Any thoughts are welcome.

A guess possible is a sticking egr .

The egr will shut closed when engine is coming back to an idle, but if it hangs up [sticks], the idle is very rough..
There was an egr replacement/upgraded part for this condition on 104s..
But, best to have codes run for true diagnosis, though.

Surging idle is also a sign of a bad MAS. Common problem...

I went to the mechanic to get the CE codes read and he got an "error" message. Couldn't figure out why we couldn't get the codes. Initially he said that I erased the codes when I disconnected the battery but later agreed when I told him that should have only reset the CE light while any codes would have remained in the OBDII module until someone erases it with the diagnostic tool. He told me to come back when the CE light comes back on. Looking back, does the ignition have to be in a certain position? He did notice when I started the car it took a few seconds (literally, not any longer) before it settled into a consistent idle . He suggested trying a few tank loads of different gas. I use Shell and ExxonMobil Premium already. I don't know, kind of frustrated that I couldn't get more information. I think I may put a bottle of Techron in the next tank and change the oil afterward. The very erratic idle, however, has not come back, but car is not as smooth in my mind as before and it still seems that starting has still been a little more labored. Is it unusual that the CE engine light has not come back on after all this?

The error code when my car was scanned was P0411, "secondary air injection system incorrect flow". That was the ONLY stored error and the CE light has come on 3 times in the past 3 months. I've done a search of the forum for the code. Does anyone have insight into this error code and the solution? Does this eliminate some of the "common" problems, i.e., sticky EGR Valve, plugged EGR tube, OVP, MAS, O2 sensor etc and/or bring some problem to the forefront? My mechanic said it could be the air pump for the system? I ask about the elimination of some of the other potential problems because it seems that there are specific error codes for the problems listed above and would be listed as the error(s) in the scan. Maybe logic doesn't always work with the infamous "CE light" error.

My observations:

Car is more difficult to start, i.e., takes that extra second to kick in. I notice all the gauge readings drop to rest (0) at the start (never noticed if that happened before, maybe more noticeable because it takes that extra second to start).

I hear what I believe is the auxilary air pump, the whirring noise, after startup which I believe is normal, but I also seem to hear it more often than before and after the engine has been run for a while and already warmed up.

Still getting the rougher idle and the occasional erratic idle even after the engine has been run for a while. From what I read does this might eliminate the EGR Valve and EGR tube because the engine is out of the cycle that involves the EGR valve and EGR tube?

Thanks for any input.

<<Still getting the rougher idle and the occasional erratic idle even after the engine has been run for a while. From what I read does this might eliminate the EGR Valve and EGR tube because the engine is out of the cycle that involves the EGR valve and EGR tube?
>>
Running the engine for a while does not stop the egr system.. it works all the time, when called for..
You are thinking of the AIR system , maybe??

Arthur Dalton:

Just a point to remember: " A little bit of knowledge can kill you, or at least make you dangerous ". :D

Here is a little info for DIYers and "Z-Techs" ..
If you are wondering about that one , he is the guy at a Dealer that is just leaning and when you go in there for a minor, not too technical of a complaint, the Service Manager says ' Hey , give this one to one of the Z-Techs !!!! .....[ "A" being a seasoned tech, and z being..well, you know..]
Heard that one yesterday from a friend who works at the local Suburu Dealership..
..hehe

Anyway , I guess any DIYer with the curiosity to go a little further
using this Forum could be called a Z Tech, without anybody hurting any feelings..


You fix anything by knowing a little about it .. then your brain surprises you and says , " hey , if this is supposed to do that and this is disconnected from them, then it can't do this ...etc..etc
What was once a very complicated problem now becomes very simple and you become very Smart...[sometimes]
So, back to AIR systems and what the hell are they/do they do/ how the hell do I fix one ??????

AIR system consist of a pump, [some belt driven, some electric] , that pumps some outside air into the exhausting air of the motor at first cold starts to help in controlling emmission. This air gets the CAT up to temp faster than w/out a pump.
The parts involved to do this are the pump, a hose with a valve between the pump and engine, and a check valve at the engine
side of the hose.
The ECU sends an elecrical signal to the pump to turn it on.
At the same time , this very same elecrical signal goes to the SWITCH-OVER-VALVE.

[A little on SOV's]--any sov [ and there are a few in your car]
is simply a valve that allows engine vacuum to flow through it when its little coil is electrically energized]

So, now we have the pump running, the sov being energized and allowing vac to open the control valve in the pump hose ,allowing air to get to the engine to do its job heating the cat and cutting emmissions.
The last little piece in the system is a check valve [mechanical] at the engine [ so gas pressure can't go back into the pump]
So, if we get an AIR code , something is not working..
First stop is to look see if maybe a vac line is off at the control valve or the SOV. No vac=no AIR. Or maybe the pump is just not getting a signal from the ECU, or maybe---well you get the idea..

Now, how does that CE lamp know something is afoul...
Simple... it does a little test that looks at the signal from the O2 sensor ...when the pump system is working correctly, it makes the exhaust very lean and the o2 sensor verifies this for the ECU..if it does not , it pops a Code and you go NuTS !!!

As SB pointed out in a recent "Scope Patterns" lesson,
a bad o2 sensor can be at fault if it does not have the capacity to READ this very lean condition..

So , when one ask for a remedy of an AIR code , I say the best bet is to know a little about the basic workings and then you can use your diagnostic abilities [ and we all have them] much better than you think...
These little ' How it Works " post are just "Basics" and intended to help those new to the different problems one runs across and hopefully to get some benefit from ....

Not if you stayed at a Holiday Inn .....

Not to be big headed but I think I'm a "Y" tech....

Are O2 sensors wear and tear items that should be replaced at a certain interval even if everything SEEMS to be running well (obviously, not in my case). For example, you know brake fluid and coolant should be changed at certain intervals even if everything seems to be performing ok.

O2 sensors
 

O2 sensors should be replaced every now and then since they have a big grey area, as in, at first they work very well, then they enter the grey area where they still work but don't give the perfect readings, and most of the time they stay in that area before they die completely at which point you will probably go bankrupt from gas bills, and change everything else in the car except the O2 in order to fix a stalling, or rough idle problem.

There is a way to clean an O2 sensor, since it is in the exhaust, the only wear and tear it is subjec to is temperature, which it is immune to for the most part, and carbon deposits which cover it bit by bit until it's too covered up to work.

You can clean it in the same manner you clean a muffler for a motorcycle, you simply take a blow torch and burn all the carbon deposits to a crips, in most cases they will catch of fire, then you scrub off the ash with a brush and it's good as new, the only problem is that in order to set the carbon deposits on fire, you have to heat up the poor O2 to a very high temp, at which point you more or less will destroy it unless you have some kind of practice, but how you get this practice I have no clue. And this is why you should replace an O2 instead of cleaning it.

xp

Given the cost of O2 sensors, I wouldn't recommend replacing them unless they fail. On OBD equipped vehicles, the "CHECK ENGINE" light will come on before the faulty sensor causes driveability problems. Also, keep in mind that O2 sensors can fail in several ways. Arthur Dalton is right on the money when it comes to the PO411 logic chain. When the AIR pump is switched on the O2 sensor voltage should drop below 40 mV almost immediately. As sensors age they may not react quickly enough or completely enough to satisfy the OBD test criteria. This sets a trouble code but the O2 sensor still functions well enough to ensure good engine performance. The EGR test criteria uses manifold pressure(vacuum)to determine whether or not the EGR system is working normally or not. A slight vacuum leak can cause EGR codes even though the system is working. "CHECK ENGINE" lights are really very simple to correctly diagnose as long as you know the parameters/ test criteria of the particular trouble code you're trying eliminate.

I think I found the problem. The plastic tubing connecting between the EGR valve and, I believe, the air pump was cracked in half under the plastic engine cover. The entire tubing was hard and brittle. For now, I had some rubber hose to reconnect the plastic tubing. I will probably replace the entire tubing when I get the chance.
I noticed that on the plastice tubing right next to the one I fixed that this type of rubber connection "fix" had been previously done. This must have been the dealer mechanics who had checked and fixed a previous CE light condition a couple of years ago. At that time they said they replaced the rubber connector and charged me over $100 bucks for the fix. I have ABSOLUTELY no problem paying them for their knowledge and skill for the fix, however, I'm a little peeved that they did not actually replace the plastic tubing that was actually the problem and would obviously crack in other places later instead of connecting the broken pieces together. Kind of half ass. That tubing and the tubing I fixed temporarily was VERY brittle (broke it a couple times trying to remove it) and obviously is affected by heat and time. Sorry, I'm done venting, moving on.

If this was the problem, will the CE light eventually go out by itself? I've read a post where someone said after a certain number of "drive cycles" without the error the CE light goes out. If true, what is a "drive cycle"? I wonder, because most of my trips are short and would they qualify to the computer as a "drive cycle"? I know I can disconnect the battery, but it would kind of nice if the car realizes by itself that the problem was corrected (affirmative confirmation).

Thanks, Arthur. That looks like that pretty much covers the problem.

Again, does the CE light eventually go out by itself? If so, what are the parameters for the clearing process? I know the code will remain until it is cleared with a scanner.

Not many options w/obd2
Battery disconnect [ don't forget radio code- ]
Scanner clearing
Auto reset..

the OBD1 systems are nice for DIYers BC you can make a $5 tool [ and some even have the tool built-in under the hood], but those days are gone...
There again, OBD2 has so much more info..
I guess a Computer interface and/or scanner may not be a bad idea for those inclined..
They tell me Auto-Zoney does it for free..

A PS on your plastic vac line , et al..
This line is a Common [ shared] vac source feed to both the EGR AND AIR SOVs, so you can see where you can get double problems with a cracked one..[ and they ALL crack..I replace the entire line w/good rubber one]

Any idea how long it takes to auto reset?