can I disable the catalytic converter sensor on my wife's car?

gm289

My wife's car has the check engine light on and she was told by her mechanic that it was the catalytic converter going out, to ignore it. I am thinking that I ought to be able to build a jumper for the sensor and fool it into thinking that it is working, reset the check engine light and wait till it starts to fall apart before replacing it. I'm tired of driving with the check engine light on, maybe missing something else that needs attention rather than the cat. it has 140k on this car but is in great condition. I am a diesel mechanic, no real experience with gas vehicles in a long time. oh, and we just got married. Or maybe I just ought to stay late at work and get this thing up on the rack and look into it. Put the scope on it myself??

gm289

Maybe I ought to call in. T and R would have fun with this call!

texases

Nope, that sensor keeps your engine running correctly. And I question the mechanic saying the cat's bad, it could just as easily be one of the oxygen sensors not working correctly. Have they been replaced?

gm289

My wife says no. Where would you start with this? I'll have to look at the scope we have at work and see if we have anything that will hook up to this car. I'm used to Cummins and Cat but not GM.

JosephEMeehan

Since the light is on except when there is no problem, your only option for getting rid of the light is some black tape over the lamp. The problem with that and with ignoring the light is that you will never know when it is telling you of a more serious pending problem that could become more serious.

Frankly why just put it off. You could just fix it.

Note: the legal issue varies from one state to another so advice you are given may well work in the state the advice giver is from but not maybe your home state.

A Flashing CEL means you should pull off that road at the first safe area. Failure to do so can result in serious engine damage and/or possible sudden loss of power. Do you want to risk your wife having her engine suddenly stop without warring?? Got a good life insurance policy on your wife?

Tester

You can't jump the O2 sensor connector to turn the light off. The O2 sensor produces it's own voltage signal to the computer. So if you jump the O2 sensor connector the computer won't see any voltage signal and will keep the Check Engine Light on.

Tester

circuitsmith

There are rumors out there that putting the downstream O2 sensor on a spark plug de-fouler will trick the system.
Just rumors mind you.

Caddyman

The down-stream sensor CAN be spoofed, but it's tricky and hardly worth the effort. I would REPLACE that sensor and see if that doesn't cure the problem..Oxygen sensors don't last forever..

circuitsmith

Me, I would look at the signals coming out of the sensors before I replaced anything.

MikeInNH

@caddyman - Oxygen sensors don't last forever..

I've replaced only ONE...and that was because the guy who did my clutch forgot to screw it back in tight. Outside of that...NEVER had to replace one...even after 300k miles. While they may not last forever..they sure to last a long long long time.

the same mountainbike

A jumper won't "fool" anything. The ECU will still not see the proper signal and will trip the light fantastic. Like Circuitsmith, I'd look at the sensor outputs before changing anything.

I found a cool site on how to interpret the O2 sensor output signals Perhaps it'll help.
http://www.aa1car.com/library/o2sensor.htm

gm289

Thanks Everyone. I checked at work today and we do have the connector and program on the computer for the stray car that wanders into our shop. I think I'll check it out this week and thanks for the O2 sensor link where I can interpret the signals. Now I feel better educated at what might be happening here. Didn't have to do much and learned a lot! I wasn't aware that the sensors relayed a stream of info to the ECM. Just thought they were NO or NC, so that's why I thought I could jumper them. Also good to hear that the sensors ought to last a long time. Thanks.

gm289

By the way, I will report back what I find. Thanks again.

Barkydog

Just as a word of wisdom, the cat signal is bad but it did not go bad by itself, but because it was made bad by another pre existing condition. Beat me whip me make me sign bad checks! The cat can only do so much, but the essence of the question is to find why the cat cannot keep up.

jtsanders

If the system at work doesn't work out for you, call any chain auto parts store near you to see if they have an OBD-II scan tool they can loan you. Many places do. You just trade your credit card for the scan tool, run your scan, and they will print the codes found. Since there's no cost, they won't scan your credit card (it's just security).

Caddyman

A couple of tenths of a volt in output can mean the difference between a CEL glowing or not glowing..While a sensor with 100K miles on it may still perform within speck, a new sensor may perform just better enough to make the computer happy and not flag you for an emissions test failure....

irlandes

I had a low efficiency cat error last year on my 2002 Sienna with 170K or so on it, now it has 183,000. I spent a lot of time Googling, because I am in Mexico, and repairs are hard and expensive. I found there is usually a sensor before the cat converter, and one after.

When the car (ergo cat) is cool, they will read the same, because the elements are not burning the crud. Once they are warmed up, the output sensor should read much lower than the input sensor. If it does not, you get a code for failure. There is no way as such to test the cat, it only compares input with output, and expects a lower output reading.

Obviously, if one or the other sensor reads wrong, it may not show a difference even if there really is a difference.

Most URL's I found said the problem seems to almost always be the sensors, though of course the cat converters can get clogged up. On my car, it failed after a 17 mile run down the mountains to Orizaba with a one mile drop in altitude, in second gear for engine braking, which means the fuel was turned off. I kept driving it and it went away and has not failed again. My guess is that long a time with the fuel injectors turned off the elements got clogged up from small amounts of oil or something like that.

Most posters here said it will come back, but so far it hasn't.

circuitsmith

"My guess is that long a time with the fuel injectors turned off the elements got clogged up"

I think the converter cooled off because with no fuel being burned the exhaust gas is relatively cold.
The engine computer had no way of knowing this, the coolant was probably still hot.
So when power was resumed the computer tested the cold converter.

Mechaniker

The output of the downstream O2 sensor can be easily mimicked by a simple circuit built on perfboard from about $15 worth of parts available at Radio Shack. The circuit ourput is a square wave, 0-0.9V, with about a 3-second period (build the circuit with trim pots to adjust the period). The ECU only looks at the rate of "zero" crossings from the rear sensor (the rate must be slower than the "zero" crossing rate from the front sensor), so any signal such as a perfect square wave will do.

The perfboard can be mounted anywhere and only requires a 12V supply and a ground. If the rear sensor has a heater, that must be simulated as well. The old sensor is left in place and electrically disconnected.

These "fake sensors" can be bought on the internet (google O2 sensor simulator), but schematics can also be found on the internet and the circuits (there are several designs) are easy to build. They require one or two ICs, and some resistors, diodes, and trim pots.

I have never seen a fake upstream O2 sensor.

Tester

Wouldn't it be easier just to repair the vehicle correctly?

Tester

Mechaniker

Tester — "Wouldn't it be easier just to repair the vehicle correctly?"

No. The OP could buy a secondary O2 sensor simulator for under $50 and install it himself in about 10 minutes. The OP wanted to save a few dollars.