CEL Oxygen Sensor

[Tim Wagor]

Recently my check engine light came on so I went to autozone and their scanner flags the front driver side 02 sensor. Replaced that sensor today and still getting check engine light. So now what? The Explorer runs fine. Any suggestions as what to do next? Could it be may Cat.?


Tim
1998 Explorer

 

[Nick C.]

did you disconnect the battery to reset the codes? Maybe get the exact code and post it on here and let some guys who have dealt with that code before give you some pointers.

 

[Tim Wagor]

Yes I did reset after changing the sensor

After checking again with scanner today the code it brings up is: P0133 upstream 02 sensor circuit slow response

What could be a cause for a slow response?

I really want to fix this myself if possible.
Any suggestions as where to look or what to replace next.

 

[BradE.]

Did they tell you what bank for the sensor at Autozone? Bank 1 or Bank 2? Knowing the idiots that work there, it's possible they told you the wrong side.

 

[Tim Wagor]

Yea I saw it for myself It was bank 1

 

[Glacier991]

Yours is a curious one. It sometimes helps to understand what the test is and what the results mean, so lets start there.

If you haven't already read it, do a search for "primer on computer control" and locate an old thread I did on how it all works. Not tooting my horn, but it was a good intro to how this all fits together.

The upstream sensor is the one the engine computer uses to fine tune the fuel mixture around the "ideal 14.9:1 (stoichiometric) setting. Ideally it will switch back and forth (crossover) across the .445 volt theshold around 8 times a minute. If it gets "lazy" it can effect fuel economy (but not a driveability issue in most cases). The computer will test it once each time you drive the car (a drive cycle test it's called - and I oversimplify). The computer will feed the fuel injection system a known signal, designed to create a predictable response from the front sensor, and the signal varies in amplitude, which should create a known "crossover" amount from the sensor. If it doesn't you will get the code for a slow response.

Ok now we know what is creating the code... but why is the Q. This is one I need to think on. I have some ideas but they are not well formed yet. Others may have some good info for you too. I'll share my thoughts as soon as I have them formed into something I think might help you.

Chris

ps. the front sensor has nothing to do with your CAT, leave the CAT alone!!!

 

[Zulu95]

Just a quick thought. It could be the wiring to the sensor. Did/can you check that?

 

[dogfriend]

What Glacier991 said plus:

 

[Glacier991]

I am thinking that maybe the ability of the computer to effectuate the necessary changes in the air/fuel ratio to properly conduct the O2 sensor test is somehow challenged. This is a case where a REAL scanner (as opposed to a simple code reader - which is what was used) would be valuable. I'd be curious to know the fuel trim numbers - that is how much adjusting the computer is doing in normal running. There are limits to how far the computer can cause a change - and I suppose if you were already up against that limit the test could not be run properly, resulting in a code. Any one of a number of factors affecting fuel/air introduction could be a contributing factor, as could external air leaks into the system (high on the probable list - and would show up in fuel trim percentages). The easiest thing to do is to get the engine hooked up to a true scnner and go from there. Otherwise you could spend a fortune replacing good components. It just seems too odd that you'd still get that code reading after replacing the O2 sensor, unless the replacement was similarly bad. A scanner would even let you watch the sensor output voltages for yourself.

Chris

 

[Tim Wagor]

Thanks for all the input on this everywone.
I'm going to do a look-over for any obvious problems again and then take glaciers advice and get a real scanner hooked up to it.
By the way Glacier, well done on "primer on computer control" You really make a seemingly complicated procedure way easy to understand. I think I'm going to bit the bullet and get my own scanner. What one would you recommend for me? Maybe I would be able to pick one up on E-bay.

Tim

 

[Red97EBV8]

I have an Auto X Ray, and I like it. Can't remember the model #. It has cables for Ford, GM, Chrysler, and OBDII. It can display sensor data real time, one sensor output at a time, and it capture 20 seconds of all sensor data that can be downloaded into a computer. Well, all the data it supports. Unfortunately, it wont read any of the Ford specific measurements unless you pay for an upgrade. I toyed around with the idea of using a laptop, but decided on a dedicated scanner because, if the laptop setup didn't work, now you have a laptop, software, and the hardware interface to debug. And the manufacturers of all three will claim that there's no problem with their product. With a stand-along scanner, only one manufacturer is responsible for the thing working.

 

[Zulu95]

AutoXray 5000!
I went through the debug process for a laptop scanner and it was the pits. Never could get it to work.
My 5000 will do just about everything and set up was a breeze.

 

[Red97EBV8]

Just checked my AutoXray, and I still don't know what model it is. It has EZ Link printed on it. That may be the model. Either way, it works great. Just used it to scan the mom mobile (Mercury Villager).