I just got a CEL that ended up being P0432 "P0432 Main Catalyst Efficiency Below Threshold (Bank 2)" but my ram has only 1 cat. Would that mean it's my pre-cat O2 sensor that's on it's way out? The pre-cat O2 sensor that's on there now was replaced at 110K and my Ram has 160K on it. I know that O2 sensors should be changed every 50K but I don't wanna just throw parts at it hoping to fix it. Thanks fellas!!!

 

That's the post-cat sensor gone south on you, unless of course the cat really is punked out.

Oxygen sensors are good for about 100,000 miles rather than 50,000. Good ones (NTK or dealer parts) are, anyway. Myself, if I suspect that one's going flaky after 80,000 I just change it out without another thought. If it does the trick, fine; if it doesn't I'm just a little ahead of schedule and that's fine, too.

 

Thanks Unreg!!! I doubt the cat is bad (can't say for sure, anything can happen) because it's only a 3 year old Magnaflow cat. I'll check into that Post O2. I thought it was only the pre-O2 that triggered CEL's.

 

to check the cat take temperature reading at front and rear of cat with a thermal laser gun 20 bucks at northern tool. the temp should be close to the same front and rear for example fr:450 rr:410 if its bad it could read fr:450 rr:310. sorry not accurate numbers just an example

 

The post-cat sensor is used solely to determine whether or not the cat is working and set a code and CEL if it seems to be failed.

When things are working normally, the PCM expects to see much less oxygen downstream of the cat than upstream of it because the cat uses oxygen to do its NOx scrubbing thing. When a cat quits working, the oxygen levels on both sides are the same and the PCM sets the cat failure code and turns on the CEL.

A working cat should be hotter at the outlet than the inlet, but it can be tricky to measure because when you're just cruising on the highway the cat's not working too hard -- the surest temperature test involves getting the engine and cat up to full normal operating temperatures then putting the engine to work by pulling a nice long grade, then taking temperature measurements as quickly as you safely can (like in a brake check pullout area). Generally, 100 degrees or more of temperature rise indicates that the cat is working properly.

Also: If your engine is burning oil, running rich, leaking coolant into the intake or a combustion chamber, or misfiring often it can destroy a new cat in very short order. Coolant in the exhaust can destroy a brand new cat in just a few minutes. Running too rich/misfiring takes a bit longer and kills the cat by overheating it with the previously unburnt fuel burning in the converter, while oil in the exhaust first causes the converter to stop working then finishes the job by plugging the cat. These same conditions will eat oxygen sensors, too.

Were it mine to do and the engine's otherwise running well, I'd replace the post-cat sensor and reset the PCM and see if the code returns after a hundred miles or so on the odometer. Of course the PCM should reset because you'll have disconnected the battery before changing the sensor -- surely you wouldn't put your PCM at risk by doing a sensor replacement with the battery connected.

 

question: is your real cat even monitored? Or, having Cali, isn't the only monitoring done on the pre-cats? Those dang pre-cats aren't cheap yo..

If it's a post cat o2 sensor, I have two brand spanking new NTK sensors I'll part with cheap.. from memory, they are the ones that end in p/n #40.. They are also pretty expensive @ $60 each if you buy from a store... If I'm not crazy, the Cali post sensors read differently (on a PCM level/Data) than 49 state sensors, and it can be tricky even trying to do the cat/delete plug mod on them..

 

So I just replaced my pre and post O2 sensors. I reset the PCM and know when I turn mon my truck, key on engine off, my GEN idiot light turns on, then off as soon as I start the truck. My CEL and oil pressure light turn on as always along with the GEN light. Is there anything I need to worry about? This just strikes me as odd since it never did that before.

 

Reset codes, and see what happens. If the code comes back fairly quickly, then worry about it..... if it doesn't.... well. Don't worry.

Do you have cali emissions on your truck?

 

I mis-spoke. When the engine is turned on, all of my idiot lights are off. I was just worried about my GEN idiot light turning on during my key on engine off phase. That's all. I also reset the code by disconnecting the battery and turning the lights on and keyed on engine off. Just overly paranoid because this is a Dodge and I'm wondering, "what next?!"...and YES, this is unfortunately a Cali emissions truck. I replaced the cat with magnaflow cali emissions cat. Cost me an arm and a leg and now it's double the price. I checked.

 

You should have four O2 sensors, and two precats right at the exhaust manifolds then, bank 2 is the passenger side.