Could someone explain to me the cause/reason behind this flag?

Also, what is the nominal O2 sensor reading, and is high rich or low rich? My car runs abnormally rich, in my estimation, by smell, and I'm trying to track down the cause... possibly a minorly bunk O2 sensor, or the ECU refusing closed-loop operation for some reason.

 

in open loop the O2 should probably be around .4V and change. In closed loop itll bounce all over as teh computer centers the mixture around stoich. If you havnt changed the O2 in a while, might as well get a new one. Look at the BLM's in winaldl and this will tell you if its rich or lean. Nominal BLM's are 128. BLM ranges cooresponding to 125-131 are acceptible. 108 is as low as it goes, which cooresponds to excessive ammounts of HC's in the exaust that the computer is trying to compensate for by leaning out the mixture. If your blms are lower then, say 120 in closed loop, then your probably going rich at idle for one reason or another.

As for teh first one, i would guess that a sensor reading or a faulty sensor is causing the ecm to come out of closed loop. maybe check for a bad CTS.

 

Wouldn't the ecu throw a code if a sensor was the cause of it going open loop? Common sense.

There's got to be a passive cause.. TRYING to get JP to answer.

 

what's an open loop?

 

Open loop refers to the mode your car is in when you start it. Think of it like a switch. Open circuit (no data recieved from sensor) / Closed circuit (data recieved from sensor).

Open circuit/loop:

[sensor]-------/ /---------[ECM]


Closed circuit/loop:

[sensor]-------/--/---------[ECM]


BTW Smurf, when my CTS went bad the ECM did not throw a code.

Later,
Harry

 

in open loop, the computer just uses its varios sensors, like tps, map, cts, etc to calculate the fueling going right off the fuel map with no feedback. In closed loop, the computer begins taking feedback from the O2 sensor to make fine adjustments to the fuel to get it to stoich. There are other things that happen as well, such as tcc lock up being enabled. The switch to closed loop is more of a transition. If one of the sensors gives a faulty reading, the computer could interprite this to mean that the motor, say for instance, has suddenly cooled down and it will then switch into open loop. It could be other sensors as well that could trigger a forced open loop but it would probably give a code. Check your readings from the ecm and see if there is anything out of the ordinary when the switch from closed to open loop occures. What t-stat do you have in the car? 180? Anything below that or an overcooling problem(like that could ever happen in a thirdgen) from a stuck t-stat could cause the computer to enter open loop with out a code being set.

 

Better than I could explain it!
I probably should have been a little more informative on this one. Although, most of the time I know just enough to get me in trouble