Hello my name is Shannon and I have a 05 Wrangler X. I have had an engine light keep coming on and off so I finally decided to have a scan run. The guy at Advance Auto says it is the "downstream 2nd bank" o2 sensor. Can anyone tell me exactly which one it is. I think I have four and they are Lt. and Rt. before Catalyst and Lt. and Rt. after. If anyone could answer this it would be much appreciated. Ty your fellow Jeeper.  

Which diagnostic trouble code? If you don't remember, just turn the ignition on-off on-off on, with out starting, three times. On the third time just leave it on. The DTC will be displayed in the odometer led's.  

Even if the guy already cleared it???  

No, it will be gone, but it'll come back. Do you remember?  

K got it! done is what it said. lol yeah it's done  

P0432 -- my guess?? Let us know when it comes back. It usually means the cat is ineffective on the second bank.

Do you have a chip/programmer on your PCM?  

I will check. Is the second bank on the pass. side??  

Can't even find the pcm....sorry  

A chip/ programmer is an after market device to reprogram the computer to give the engine more performance. They can cause problems with O2 sensors and catalytic converters. Do you know if one has been installed?

Don't worry about anything until you can tell us the code. Then the advice can be very specific.  

k ty and no then no mods have been done. Ty for your help.  

I have a question similar to Shannon's. My code is 21 so how do I know what sensor it is or if is some other underlying problem causing the sensor to trigger such as too lean or too rich a mixture. I have a 97 Grand Cherokee 6. thanks  

An MIL 21 is an alert that the O2 sensor is slow responding to air/fuel mixture changes.

If this is the only code ie no mis-fire codes, this usually means a bad 02 sensor. Either the sensor, the sensor heater or the wiring to the sensor could cause the PCM to raise this exception. Further testing needs to be done to determine the exact cause.

This does not indicate a rich or lean condition, just a slow reaction of the O2 sensor's ability to detect a lean or rich condition.  

I have an 04 Rubicon Wrangler with a hypertech programmer.  Recently, I received a P0432 DTC.  What can you tell me about this situation?  If I remove the program and bring it back to stock, will it cure my issue?  Or am I to begin diagnosing for a back O2 sensor?

In advance, thanks for your advice.  John  

Cats don't normally just wear out or fail. They fail for one of three reasons. Overheating, thermal shock, or contamination.

Contamination is usually a side effect from other engine problems. A blown head gasket, allowing antifreeze into the exhaust, or bad valve guides allowing oil into the exhaust.

Contamination coats the catalyst, rendering it inaffective.

Thermal shock is usually caused by a hot cat coming into contact with cold water or snow. This causes the cat to cool very quickly and causes the catalyst to break apart and clog the exhaust. Poor performance is usually noticed.

Overheating is caused by too much fresh fuel entering the exhaust. The cat is an oven. It is designed to burn left over fuel from the combustion cycle. When the engine is running well, i.e. all systems functioning correctly, there is very little unburned fuel in the exhaust.

There is an O2 sensor before the cat and an O2 sensor after the cat.

The first O2 sensor is used by the computer to determine the adjustments needed to the air/fuel mixture during "closed loop" running.

The second O2 sensor's reading is compared to the first O2 sensor's reading. If they are the same, that indicates that the cat is not burning the unburned fuel (cat inaffective - P0432). When the cat is working correctly, the second O2 sensor's reading will indicate lean, meaning all fuel has been burned.

Closed loop is a set of driving conditions, dictated by the ODB standards (EPA compliance), that must be monitored for emissions output. Idle and cruising being the main events.

During closed loop processing, the computer makes adjustments to the air/fuel mixture when it is determined to be too lean or too rich as indicated by the upstream O2 sensor.

Wide open throttle (WOT) and accelerating are two driving events that cause the computer to go into "open loop". During open loop, there are not any adjustments made to the air/fuel mixture, and the O2 sensors are not used as inputs by the computer with regard to air/fuel mixtures.

Open loop is the opportunity that programmers/chips have to f-with the fuel maps and not cause emissions related "violations".

Basically, dump in a little extra fuel when the cops (O2 sensors) aren't looking.

So, depending on your driving habbits, extra fuel is being dumped into the exhaust causing the catalytic converters to overheat and eventually fail to be effective.

Here are some other things to check when resolving a P0432 DTC:

Check for exhaust leaks.

How is engine performance? Any misfiring? Any other codes stored? Rough idle? Etc.

Check for TSB's (technical service bulletins).

Check for any computer updates or PCM re-flashes.

Check for vacuum leaks.

Thoroughly inspect the upstream AND downstream O2 sensors for poor performance. This requires a scan tool.

Excessive heat can also cause damage to the down stream O2 sensors. Sometimes they will go bad before the cat is damaged from the side affects of the programmers/chips.

If any of the above are present, they should be taken care of before the convertor is replaced. After the repairs, clear the codes. This is only the first step in repairing the failure and the vehicle must now be driven for several days or weeks so the PCM can monitor the convertor performance.

Federal law mandates that the emissions system on a vehicle be under a very long warranty. The dealer will resolve an emissions related DTC and replace your converter for free. But, not if they see evidence of a programmer/chip.

The Jeep engineers are not stupid. They purposefully de-tune the engine slightly to give you the best in performance, drivability, emissions, longevity, and fuel economy.

These are the things that the programmer/chip manufacturers ignore to give you a little performance.

In my opinion, the increase in performance is not worth the reduction in fuel economy, the price for premium fuel, and the negative effects on longevity.

Are you running larger tires? If so, have you re-geared. Gearing will perform like a 30hp increase.  

Is the downstream even needed in an off-road-only Jeep?
Besides the MIL always being on, are there any other problems to be expected? (my cat was removed for comp use only)
If I create a steady .45V signal on the downstream, will the PCM think everything is kosher?
2000 4.0 TJ
THANKS