upersman

I have a 98 xj. CEL is on and the code reads 0171. I checked and the code is:

171 The oxygen sensor is saying that the system air/fuel mix is far too lean (too much fuel is being added as a correction).

What do I do. I'm not very mechanical, and I'm not sure if I need to replace one 02 sensor (don't know which one) or both. Not sure if it is something else. If anyone here has had a similar experience, and was able to fix it, I would appreciate some advice.

As always, thanks.

2doorxj

lean is air i could be 100% wrong but it sounds like it's starving for fuel. check the line pressure and make sure the injectors are clean. also the code should tell witch 02 bank 1 or bank 2. hope i somewhat helped

upersman

I don't think it's starving. Gas mileage is bad, and you can smell the exhaust; it's getting too much fuel.

2doorxj

to much would read rich though, i'l ask a few friends and get back to ya

mdtobe

It seems backward, but this 0171 "too lean" code DOES mean it's running too rich.

Basically, it means the O2 sensor has failed. When this happens, the O2 sensor THINKS it is too lean and keeps trying to make it richer and richer. Basically, meaning it has failed. When the O2 sensor fails, it goes into the default open-circuit mode, which sets the injection system to go to full-rich.

I've been having the same problem. But in my case, something is making the O2 sensors fail over and over. My mechanic has replaced the front sensor twice, and the back sensor once. And the Catalylist once (during the replacement of the 2nd front sensor). Everytime, he claims he's checked everything that could make the O2 fail. And everytime, within a few weeks to a month, the NEXT O2 sensor fails. Not happy!

So now I'm trying to figure out the problem myself. Which is why I've joined this forum.

Back to your situation:

Hopefully, you simply have a failed O2 sensor - they do wear out after around 100,000 miles or so. On the other hand, if you're problem's like mine and something is causing your O2 sensor(s) to fail, it could be several different things:

Fouled plugs and/or bad wires
Bad MAP sensor
Bad or plugged injectors
Antifreeze leaking into combustion system (Phosphates in antifreeze coats and kills O2 sensors)
Oil leaking into combustion system (Oil coats and kills O2 sensors)

Best of luck to you,

John

tjwalker

The #1 cause of this code is a vacuum leak. Although it is possible that it is the oxygen sensor, it probably is not.

Perform a comprehensive search for a vacuum leak. Also a small exhaust leak can create a condition that can trip this code.

Even bad secondary ignition such as wires/plugs/cap/rotor in certain situations, but less likely, and you will usually have an accompanying misfire code.

Replacing oxygen sensors with 100k - 150k is not going to be wrong just because they do get lazy over time and have a finite life span, but my gut is that this is something else.

I've seen O2 sensors installed for this code before (multiple times) when the root cause was not that.

Vacuum leak. Exhaust leak. You must verify that you do NOT have one of these before looking elsewhere.

Also would be a good idea to get a fuel pressure GAUGE and verify your fuel delivery. You should have 49 psi at idle for a 98.

Good luck!