Question About " Open Loop "

hi, everybody, i am new here.

i 'd like to know about the " open loop "
i know already the "open loop" happens when

1. the engine is too cold .
2. the temperature is too low to get O2 sensor work
3. O2 sensors fail
4. wide open throttle plate

anyelse?, i heard about the " deceleration" and "idle", is it ture? why?


thanks so lot.

"Open loop" simply means the engine control unit doesn't use feedback signals to modify it's behaviour.
Basically it sends instructions to the engine but doesn't modify those instructions based on information it gets back. Usually because the sensors that normally send it feedback are too slow to react in those conditions.

The opposite of open loop is closed loop. This means the controller continually modifies it's instructions based on the feedback from sensors.

thanks body,

i just like to know when the engine ignore the feedback?
does it ignore the feedback during decelaration or idle?

thanks body,

i just like to know when the engine ignore the feedback?
does it ignore the feedback during decelaration or idle?

Its depends on the engine.
They are all different.

WBO2 systems pretty much never ignore the sensor, and its always in closed loop, decel, WOT etc. The only time they aren't in closed loop is for the first 10 or 20 seconds of a cold start, which is how long it takes for the sensor to heat up.

For NBO2's, with a heater circuit (3 and 4 wire) they pretty much follow your list of when they are open. Non-heater (1 and 2 wire) are less reliable at idle and usually are either ignored....for the most part

appreciate it

that is why i ask the question

a 98 malibu, v6. after changeing the intake manifold gasket, the idle speed seemed to be a little bit low, engine ran roughly, and the check engine light on. check with the scan tool, the code showed the TPS problem.( forgot the exact code number). the TPS signal is 0.59v in the idle.
I cleaned the throttle body and the IAC motor and passage. it seems the idle speed increase and engine running much better. but after i erase the code and drive the car, the same code came back again.

is the 0.59v is good for the idle ?. i heard 0.5v is correct.
does the TPS cause the engine running rough? why?

without knowing which code it is, no idea.

If the computer is sensing something wrong, it can definitely make it do some odd things

thanks, unclebob

i'll find out the code tomorrow. thanks again

Technically, GM PCMs don't fully "ignore" the inputs when in Open Loop Mode or PE Mode (or even in Backup Fuel and Spark Modes) but don't use the input data to modify outputs. If you want to verify that, strap your car on the treadmill/dyno, run it at WOT, and unplug a primary O² or the MAF.

no doubt that would set a code. I think its mainly using the (NB) O2 reading to verify its not going lean at that point. Not completely ignoring it, but definitely not much of a factor.

Unplugging the MAF is a whole nother deal though. Most MAF systems prioritize the MAF over the O2 even at <WOT

Technically, GM PCMs don't fully "ignore" the inputs when in Open Loop Mode or PE Mode (or even in Backup Fuel and Spark Modes) but don't use the input data to modify outputs. If you want to verify that, strap your car on the treadmill/dyno, run it at WOT, and unplug a primary O² or the MAF.

The difference between knowing there's a signal and not using it or the controller throwing it's toys because it knows something is missing.

The MAF is required to run even in open loop as that's a driving signal, but the O2 sensors are only a modifier needed to run closed loop.