Check Engine Light - Code 430

[ScottLemieux]

Hello Everyone!

I'm one of those long time lurkers! And would like to thank everyone who unkowningly has helped me greatly in the past!

I've got a 1997 Explorer Eddie Bauer with 5.0L V8 with 117,000 miles. The other day my Check Engine light came so I took it to Autozone and got the code:

430 - Catalyst System Efficiency is below threshold (Bank 2)

The guy at autozone fiqured it was a O2 sensor and from everything I have seen in the forums regarding 420 code (haven't found any mention of 430) I would guess it's the O2 sensor as well. I have no other problems, truck runs fine. Gas milage has dropped from 18 miles/gallon to 16 in the past couple months which I attributed to needing a tune-up which I plan on doing next week.


Think this is just a O2 sensor? What else should I check? I didn't have the guy at AutoZone reset the code, should I reset it by disconnecting the battery and see if it comes back or am I just asking for more trouble?

Thanks!

 

[mrboyle]

Normally that code is related to cat failure, not O2 sensor failure. What it means is the difference in the air entering the cat (front O2 sensor) vs. the air exiting the cat (rear O2 sensor), is not meeting the required reduction in emissions. You may need to have the cats tested.

 

[wallygetsit]

Was this ever solved?
If so, could you tell me the problem.
I currently get that error, clear it, and then it comes back every few days.
The truck is running great. Just had a trip to Toledo and back and got 22.6MPG. (Typically average 20.5)
Sounds like to me that that code is saying that too much exhaust is making it thru the cat without being "sanitized". That might actually increase gas mileage, and kill the atmosphere all at the same time.

 

[Billy177]

try switching the o2 sensors wit the 1st bank and see if the code from the other bank comes up

 

[wallygetsit]

Does anyone know how to test an actual O2 sensor?
Resistance?

 

[aldive]

Originally posted by wallygetsit
Does anyone know how to test an actual O2 sensor?
Resistance?

You can measure the function with a scanner,

 

[wallygetsit]

I would think there should be a way to test it with a simple digital multimeter (DMM).

An open would read extremely high resistance or a short would read extremely low resistance (<1.0ohms).

A good O2 sensor should have a "good" range somewhere in between when unpluged from the system.

 

[Glacier991]

An 02 sensor has a threshold crossover voltage of .445 volts. The 02 sensor produces voltage (as opposed to varies in resistance) in proportion to temperature. The front sensor is used to fine tune the injector pulse width, hence adjusting the mixture lean or rich. It's a chase the tail setup, and the sensor, if healthy, will "crossover" that threshold voltage at least 8 times a minute, or more as the mixture continually is fine tuned back and forth across the "ideal" mixture (14.7 to 1, sometimes by people who like to use big words also called stoichiometric). If you use a scanner you can watch the voltage vary, directly right on the scanner readout - for all sensors! That's one of the reasons I love my scanner (NOT reader). On older cars (pre95 or so)there are testers that can puncture the sensor wires and do the same thing more or less (I tried to sell an extra one I own in the for sale section here and no one even looked at it).

You might find some useful information in this thread, and see the actual display of voltage on a scanner!:

http://explorerforum.com/forums/showthread.php?s=&threadid=80707&highlight=Scanner+vs+Code+Reader

Similarly, this thread on a computer controlled engine may also help you better understand what is going on.

http://www.explorerforum.com/forums/showthread.php?s=&threadid=80692&highlight=Computer+Primer

The "after cat" or "downstream" sensor is used to see if there is still any unburned fuel coming through the cat, becuse if there is, it too will vary the voltage output as the mixture changes. If the cat is able to handle all unburned fuel, the downstream 02 sensor should more or less be flatline in it's voltage output. If it is not (in other words if it approches a response similar to the upstream 02 sensor), you get a code 420 or 430. Lots of things can cause that, besides a bad cat. Me ? before I'd pop for a new cat or 02 sensors, I'd get a scanner on it and SEE what's going on, instead of guessing or blindly replacing expensive parts. Sometimes simply replacing spark plugs and plug wires can solve this problem! Do not just assume the cat is bad. It may be, but also... may not be. Check systems. Fuel, ignition, check sensors (MAF and TPS) etc.

Happy Exploring

Chris

 

[wallygetsit]

Wow, thanks for the reply.
I am looking into investing in a scanner.