P2096 or P2098 Post Catalyst Fuel Trim System Low Limit

DOSneons · Post by **DOSneons** » Sat Dec 20, 2008 5:59 pm

what does this code mean?

P2096 or P2098 Post Catalyst Fuel Trim System Low Limit

Donkeypuncher · Post by **Donkeypuncher** » Sat Dec 20, 2008 10:46 pm

Sounds like the downstream O2 sensor is going bad, or the catalytic converter is bad. However, the fuel trim is usually calculated from the upstream O2 sensor so I'm not sure why it's described that way.

DOSneons · Post by **DOSneons** » Sun Dec 21, 2008 3:14 pm

thats what i figured i have a small exhuast leak so ill just need to replace those

Post by **occasional demons** » Sun Dec 21, 2008 9:15 pm

http://forums.neons.org/viewtopic.php?f=8&t=308847

ACR MAN wrote:
chipdogg wrote:How would it use the downstream 02 sensor for fuel trims?
The 1996-2008 stock PCMs use the downstream O2 sensor for the catalyst efficiency monitor and for the downstream fuel control strategy.

The PCM has a programmed goal voltage for the upstream O2 sensor. This could be thought of as the average voltage (over time) that the PCM wants to see from the upstream O2 sensor. Prior to 1995 this was thought to be .5 V, but in reality that was not necessarily the case on Chrysler products even in the early 90's.

The upstream O2 goal voltage can be changed by the PCM based on the behavior of the downstream O2 sensor, within certain parameters. The PCM expects to see the downstream O2 sensor at a particular voltage (which indicates efficient catalyst operation) when the engine is operating within each particular RPM/MAP breakpoint. This is a calibratable value which is programmed for each engine package. If the downstream O2 sensor is reading a lower voltage (higher oxygen) than the PCM wants, then the PCM will react by moving the upstream O2 sensor goal voltage higher. This will provide marginally more fuel which will alleviate the "excess oxygen" problem. If the downstream O2 sensor is reading a higher voltage (less oxygen) than the PCM wants, then the PCM's reaction will be the opposite: to move the upstream O2 sensor goal voltage lower which will provide less fuel.

Note that you can read the upstream O2 sensor goal voltage on a DRB III, StarSCAN or StarMOBILE scan tool, but the "desired downstream O2 sensor voltage" (for lack of an official term) is not displayed on the scan tool.

DOSneons · Post by **DOSneons** » Mon Dec 22, 2008 3:32 pm

u lost me lol

Post by **occasional demons** » Mon Dec 22, 2008 4:49 pm

Basically it explains the fuel trim low limit on the downstream sensor. Since you stated you have an exhaust leak, if it is before the downstream o2, that would explain the low limit code. It prolly has added all the fuel it can to attempt to correct the "lean" condition, and still reads at the low limit. So it sets the CEL. Be happy you got one. Me and a few other ppl have had cracked manifolds, and all kinds of weird symptoms, but no CEL. When it is a small crack that doesn't make noise, and isn't visable till you remove all the sheilding, it makes for some frustrating truobleshooting.
A lot of ppl don't believe the downstream o2 affects anything, but it does. I have had a downstream go bad, and I have gotten worse mileage from it. The above post explains why. I had just read it, and it related to your code, so I thought I'd share.
It brings more truth to a what a Chrysler tech told me; that o2 sensors should be replaced in pairs, as much as it pains the wallet.

DOSneons · Post by **DOSneons** » Wed Dec 24, 2008 9:03 pm

ok well i was told i could go to a auto parts store and buy a non-fouler tip for a sparkplug and drill the hole to 5/8 and screw the o2 sensor into that and put it back into the exhuast and it would pull the sensor out of the airflow and eliminate the code

Post by **occasional demons** » Thu Dec 25, 2008 9:07 pm

Sometimes it works, sometimes it doesn't. It is cheap enough to give it a shot.

Donkeypuncher · Post by **Donkeypuncher** » Thu Dec 25, 2008 9:55 pm

Are you running without a cat converter? That's what people use to get rid of the usually cel for that.

According to demons info, a low limit means you're already seeing too much oxygen. That might just make it dump more fuel and make you run pig rich. You're best bet is to fix the leak first, otherwise it just might run worse. That's if I'm reading that quote correctly.

DOSneons · Post by **DOSneons** » Sat Dec 27, 2008 8:05 pm

i am runnin a cat, but ive had the leak fixed three times but i keeps comin back.