Check engine soon light on
Burning Brakes
Joined: Dec 2006
Posts: 936
Likes: 2
From: Tyrone PA
The older L98s (all L98s, I think) have only one O2 sensor. The ECM sets a code when it receives a reading (from any sensor) that doesn't match the range of readings it is programmed to expect to receive under the conditions described by all the other sensors. In the case of the O2, not only is a code set, but the ECM knows not to rely on the O2 for feed back in fueling in closed loop and reverts to preprogrammed fuel tables (open loop). A car with more than one O2 can tell you which bank of cylinders has the malfunction. With more than 2 O2s, #3 and #4, if present, monitor cat function and efficiency. That is pretty basic. Does it give you what you wanted?
RACE ON!!!
RACE ON!!!
Former Vendor
Joined: Nov 2006
Posts: 2,482
Likes: 3
From: Carmichael ca
Bank 2 sensor 2 is the one after the cat on the passengerside. It should be available from most parts stores. It would be a good idea to have it checked by someone with a scan tool to see the actual readings its sending to the ecm, before replacing it. Also check the wiring going to the sensor to be sure it wasn't damaged during the exhaust install.
Good Luck, Paul
Good Luck, Paul
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Bank 2 sensor 2 is the one after the cat on the passengerside. It should be available from most parts stores. It would be a good idea to have it checked by someone with a scan tool to see the actual readings its sending to the ecm, before replacing it. Also check the wiring going to the sensor to be sure it wasn't damaged during the exhaust install.
Good Luck, Paul
Good Luck, Paul
Circumstances sure suggest damage of some sort occured durint the exhaust upgrades..
Thread Starter
Intermediate
Joined: Nov 2007
Posts: 29
Likes: 0
Can you explain open loop?
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by andrew.huh
I m waiting for the check engine light to come back on. The guys at the muffler shop used a sensor scan, not sure exactly what it was but turned the light off. But the light will come back on if I keep driving. I m thinking that its probably best for the light to be on so I will know by installing the new sensors that the problem is fixed. I will ask to go by what everyone is telling me. I do not know what open loop operation means. Could you explain? Thank...
Never trust a code to tell you what a problem is. The code only identifies the device that sent the out of parameter reading. The reading can have many other causes than the device being bad. Always trouble shoot to isolate the CAUSE of the problem or code. Don't just throw money (parts) at a problem. Diagnose it and fix the real cause, the first time.
Once the real problem is corrected, the Check Engine Soon light, will not automatically go off. YOU need to reset the codes and keep your fingers crossed the problem is cured and that the light doesn't come back on.
It would appear you could benefit, a lot, from the FSM, Factory Service Manual.
RACE ON!!!
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Thread Starter
Intermediate
Joined: Nov 2007
Posts: 29
Likes: 0
open loop
Open loop is when the car runs off of preprogrammed values that are programmed into the computer. Closed loop, which is supposed to occur after a given time delay and engine temp, is when the computer adjusts the A/F mixture based on the feed back from the O2(s). The loop is: O2 reads exhaust-> report to computer -> computer adjusts the A/F mixture -> exhaust changes -> O2 reads exhaust. That makes a circle or a loop. When the loop is not complete, such as when the O2 sensor isn't hot enough to send meaningful info, the loop is broken, or open.
Never trust a code to tell you what a problem is. The code only identifies the device that sent the out of parameter reading. The reading can have many other causes than the device being bad. Always trouble shoot to isolate the CAUSE of the problem or code. Don't just throw money (parts) at a problem. Diagnose it and fix the real cause, the first time.
Once the real problem is corrected, the Check Engine Soon light, will not automatically go off. YOU need to reset the codes and keep your fingers crossed the problem is cured and that the light doesn't come back on.
It would appear you could benefit, a lot, from the FSM, Factory Service Manual.
RACE ON!!!
Never trust a code to tell you what a problem is. The code only identifies the device that sent the out of parameter reading. The reading can have many other causes than the device being bad. Always trouble shoot to isolate the CAUSE of the problem or code. Don't just throw money (parts) at a problem. Diagnose it and fix the real cause, the first time.
Once the real problem is corrected, the Check Engine Soon light, will not automatically go off. YOU need to reset the codes and keep your fingers crossed the problem is cured and that the light doesn't come back on.
It would appear you could benefit, a lot, from the FSM, Factory Service Manual.
RACE ON!!!
Burning Brakes
Joined: Dec 2006
Posts: 936
Likes: 2
From: Tyrone PA
You said the light went off because the mechanic cleared the code, right?? Did the light come back on yet? is it possible that the sensor was crudded up or something was amiss in the exhaust, like grease or residue burning off, that made the sensor give an abnormal reading long enough for the ses light to come on? If that is the case then the light won't come back on as there is no problem. As long as your light is off I don't think the computer is seeing any problems and I think it is operating as normal. I'd run it till the light came back on before I'd change any sensors or anything.
Thread Starter
Intermediate
Joined: Nov 2007
Posts: 29
Likes: 0
You said the light went off because the mechanic cleared the code, right?? Did the light come back on yet? is it possible that the sensor was crudded up or something was amiss in the exhaust, like grease or residue burning off, that made the sensor give an abnormal reading long enough for the ses light to come on? If that is the case then the light won't come back on as there is no problem. As long as your light is off I don't think the computer is seeing any problems and I think it is operating as normal. I'd run it till the light came back on before I'd change any sensors or anything.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
cleared the code
sounds like they found the sensor unplugged, or the wire touching something, and now it's fine.
I would drive it till the light comes back on. Being obd ll theres a lot more codes and the computer does a trend model, and anything out of the trend is considered failing. It will throw a code for that.
CFI-EFI referenced fueling. The computer will map a trend when you fuel it. You have to fuel above 3/4 tank.
I would drive it till the light comes back on. Being obd ll theres a lot more codes and the computer does a trend model, and anything out of the trend is considered failing. It will throw a code for that.
CFI-EFI referenced fueling. The computer will map a trend when you fuel it. You have to fuel above 3/4 tank.
