If the O2 sensors go bad this will trip a code, right? Autozone and others advertize to replace these every so many miles, is this really worthwhile if there are no codes showing? Or is this just them trying to sell O2 sensors?

They also say to replace these to get better gas mileage.........


1999 Ford Ranger, blue, stepside, 2.5Ltr, auto, 2 X 2

Have you driven a Ford lately?

 

They are just trying to sell O2 sensors.

 

They will set a code if they fail outright, but they might start performing poorly.

I think that they do a few more comparisons now that they have pre and post converter sensors, but I think that they can still have performance problems that won't be reported.

There is a condition known as a 'lazy' O2 sensor that doesn't respond as fast as it should.

There are also conditions that cause them to read rich or lean. Since the computer uses them to verify the fuel trim this can cause problems -- it will try to correct the fuel trim to match the O2 sensor.

However, if your truck is running OK, they're probably OK. FTE folks seem pretty sensitive to performance ( myself excepted), and this is how you might guess that there was an issue. (running rich, etc)

 

I had a O2 sensor that was pooched and it did not throw a code.

 

but "lazy O2 sensor" may be easily checked with OBD-II data monitoring. Suffisticated scanners/ELM 327 PC software makes diagrams and you can see how "fast" is your O2 sensor. Usually time of respond is about 0.5-1 sec. if o2 sensor is in manyfold near cyl head (newer EU cars) and 2-3 sec if it is in exaust pipe near under truck cat. It is funny but O2 sensor may be dirty and that's why lazy.

 

Autozone would never try to sell you parts only dealerships do that! (ha ha!) They only offer free information don't they? ford2go is correct though you can get what is called a lazy 02, you can see that with a good scan tool, however if one goes bad they usually throw a code. I do work at a dealership and I diagnose the problem and inform the customer justly I wont just throw parts at it. It's wrong to do so.

 

Usually if engine is old ore birns oil lazy O2 sindromes appeare. Bad fuel cause O2 problems too. Driving with permanently cold/not warmed up fully engine (i live in 3 miles far from my work but when it is -15-25 dgr C outdoors any car truck are warmed up in 5-7 miles. So when I approach to my work I have +50-60 dgr c collant temperature... as result too early death of oxy sensor

 

Yes, a bad or failing O2 may or may not throw a code.

I don't know about your local AutoZone, but when I ran mine I enforced a strict policy of NOT selling parts that weren't needed, and NOT padding tickets with unnecessary add-ons. I bounced more than one opportunist for trying to take advantage of a customer. And as a result of that policy, my store was far and away more trusted than the one across town - not to mention half the dealer's shops in town.

And we didn't charge a half-hour (and up) diagnostic time for pulling codes like the dealers did (and still do).

 

I replaced mine at 85,000, just as general maintenance

 

Allow me to explain the way in which the sensors will fail, and the consequences of said failure. I will not go into the details of how they work, as such information is readily available on the internet.

As the sensors age, and develop deposits on their reactive surface, their voltage outputs will weaken. The decreased voltage mimics the behavior or a lean mixture. The computer unable to distinguish between the two will increase the injector pulse width to compensate. This results in rich operation, and decreased fuel efficiency. this can go on for quite some time, so long as the sensor meets certain minimum performance requirements. So long as it reacts to changes within a certain amount of time, the sensor is assumed to be good, regardless of how inaccurate it may be.

The need for a new O2 sensor can be determined by looking at the long term fuel trim in the computer. This most often does require a more advanced scanner, so unless you have a top of the line code scanner, you may not have access to this information. The fuel trim is basically the amount of adjustment that is needed to get a desirable reading on the O2 sensor. This value should be within ±2%. If it is not within 2%, there is a problem, and the O2 sensor is the most likely culprit, since it is the only sensor that adjusts the fuel trim. However, anything that can deceive the O2 sensor, such as unmetered oxygen in the exhaust due to exhaust leaks can also show up in fuel trim data. Also anything that foul or deceive the sensors used to determine the fuel trim reference point should also be considered. These sensors are the MAF(Mass Air Flow) sensor, the ECT (Engine Coolant Temp) sensor, the IAT (Intake Air Temp)sensor, and the TPS (Throttle Position Sensor.) The Long Term Fuel trim is often overlooked because it can't tell you what is wrong, but it should be looked at because it can tell you that something is wrong, even if that something does not set codes.

 

Are you detecting any performance issues? If not I'd wait until you throw a code. You have to start somewhere. Bear River is right. Even when you have a code that is just a starting point. I generally view the MAF sensor as the most problematic. Not to mention that it is hard to know whether to rely on the parts store guy or not, unless you know his qualifications. Otherwise you are potentially hanging expensive parts.

 

If in doubt change it out. Only like 30 bux.