Open Loop Mode = Good - Third Generation Forum

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Open Loop Mode = Good
Tuesday, July 19, 2005 5:07 AM
Hey guys,

Going to try to explain my problem with as much detail as I can think of thay may be useful... Ok, some time ago I started getting a CEL that I have since erased a few times (3-4 with a scanner) only to come back on within about a day. Now I had read that disconnecting your battery for some time will also result in resetting the light which I have done a couple times while installing audio equipment. Now the funny part is when I have done this the car runs GREAT when the CEL is not on. As in, after the battery is just re-connected and the computer is running in Open Loop mode, sure my gas mileage might not be great at this time but the car runs like a champ, then as soon as I get my CEL back (P0440) it starts to bog down sometimes, seems like a loss of performance, wants to stall out sometimes at stop signs, lights, etc... sometimes it actually does stall, and when I shift the RPM's drop quickly as opposed to normal, it's almost like a completely different car, but then if I unhook the battery overnight and drive the next day the car is great until I get the light again. Any ideas? What are some causes of a P0440 that would do this? I realize it's a leak in the EVAP (Heard it could be a cannister by the fuel tank) but would this cannister cause the car to run like crap only AFTER it's been noted by the ECU that it's not functioning properly or is it that the ECU is learning some wrong values for something? I'm not entirely sure how the learning process works.

Re: Open Loop Mode = Good
Tuesday, July 19, 2005 6:34 AM
what year make model is your car?
Re: Open Loop Mode = Good
Tuesday, July 19, 2005 6:42 AM
2002 LS Sport w/Ecotec (Canadian Z-24)
Re: Open Loop Mode = Good
Tuesday, July 19, 2005 7:08 AM
p0440 is an emission code. it means that your catalytic converter is not functioning properly. if the converter is clogged, it is likely what is causing your stalling and missing

your computer runs in open loop mode whenever the cel is on, and upon starting the vehicle.


Re: Open Loop Mode = Good
Tuesday, July 19, 2005 8:22 AM
Hey JB,

Sorry I must have gotten the two mixed up, I mean closed loop mode. This is what I get for a listing of P0440 - DTC P0440 Evaporative Emission (EVAP) System - I have read quite a few posts on here relating to this code that have indicated that in most cases on 2002+ vehicles it is a broken wire that attaches to the EVAP cannister next to the gas tank. I could be wrong though, other sites indicate that p0440 is EVAP Emission System - Large Leak. So I'm not sure but it doesn't sound like the CAT to me. This to me sounds more like a CAT problem - DTC P0420 Catalyst System Low Efficiency. ANy thoughts?
Re: Open Loop Mode = Good
Tuesday, July 19, 2005 9:37 AM
Have you checked the fuel cap if it is damaged that can cause a code to set.
Check for kinks in all of the hoses. There are many reasons that can cause the light.
Re: Open Loop Mode = Good
Tuesday, July 19, 2005 9:49 AM
JB (teh j00ced one) wrote:p0440 is an emission code. it means that your catalytic converter is not functioning properly. if the converter is clogged, it is likely what is causing your stalling and missing

your computer runs in open loop mode whenever the cel is on, and upon starting the vehicle.



P0420 is for a possible bad cat. P0440 could be a gas cap, canister or even a corroded wire. I got the P0440 code and a wire that went to that canister was broken.....replaced wire and no more problems.



Re: Open Loop Mode = Good
Tuesday, July 19, 2005 10:05 AM
Hey J R,

Fuel cap is good, I am not so much wondering what the problem that is causing the code is as much as why the car runs PERFECT until the code finally sets in, and then runs like crap.
Re: Open Loop Mode = Good
Tuesday, July 19, 2005 10:28 AM
the car is going into what they call LIMP MODE,it is a pre programed memory that kicks in when the computer does not Know what to do.You get signals from sensors that tells your computer everything it needs to know to run the engine. So when there is a problem the car will still get you were you need to go. If you fix the problem then it wont go into limp mode
Re: Open Loop Mode = Good
Tuesday, July 19, 2005 10:37 AM
Ahhh ok... so regardless of what the problem is that's causing the CEL the car will always run somewhat sluggish when the light is on? So this isn't necessarily a mechanical problem causing the car to be like but rather the ECU is no longer fluctuating, just maintaining one set of 'instructions'?
Re: Open Loop Mode = Good
Tuesday, July 19, 2005 10:46 AM
well the light by its self wont make you go into limp mode just certain codes that pertain to driveabilty problems,

Just like on my 04 cav I unplugged the vss sensor,the only thing that the computer uses it for is ABS,speedo,odometer and governor. The engine light is on but the car does not go into limp mode.

Re: Open Loop Mode = Good
Tuesday, July 19, 2005 10:59 AM
J R wrote:well the light by its self wont make you go into limp mode just certain codes that pertain to driveabilty problems,

Just like on my 04 cav I unplugged the vss sensor,the only thing that the computer uses it for is ABS,speedo,odometer and governor,it also is used for auto's and there shift times. The engine light is on but the car does not go into limp mode.

Re: Open Loop Mode = Good
Wednesday, July 20, 2005 6:04 AM
i duno. my diagnostic tool is way out of date. it comes up as cat not functioning for p0440. yet i also get the same read out for the p0420 code.
i just assumed it was correct since the code started showing up immediately after i had installed my high flow cat.


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