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Holton345 06-23-2013 10:25 AM

2003 Sport CEL Throwing "P 0171"
The old 2003 Sport I bought the other day is throwing a 171 at me. I know this means it is running lean.

I bought it the other day from an individual and had a dealership do the same inspection that they do on their certified pre-owned stock in-house. (I know, I know. But it made me feel better about my own inspection to have them back it up for me...) They also checked some other stuff for me by request, as it has some suspension changes and some body mods...

It was blessed as being in very decent shape but in need of a few things that I already had determined needed replacement.

So I go to pay for it. (Cash money, man. No freaking payments!)

As I drive away in my new-to-me baby the CEL comes on. I groan. Rather than go back and fuss at the seller (since both the inspector and I liked this rig) I decided to go back the the dealership and get the OBD II read.

It was a 171. Everyone wanted to know if we had just put gas in the thing. This is baffling to me. Why would you get a 171 (running lean) after a new tank-up? But that is what they all first asked me.

I was told a very vague "bad gas" bit and told that it had been cleared and to fill up. That it would be okay regardless, that it would probably not come on again once fresh gas was in the system. (I suppose they thought it had been sitting for some time?)

They were correct. I drove 243 miles with two stops for gas. Mileage sucked, as you would guess. But the CEL never came bak on.

I figured my mileage using actual miles traveled and not the odo reading as it has the wrong speedo gear. It came out to 13.9 mpg. Not good. So I knew that night that we had a small problem somewhere.

The next morning I backed it out to take some photos for friends on FB. I cranked it up and the dang CEL came on again. I could not check it at the time as I had to take an overnight trip.

This morning I ran the code and it was - again - 171.

If it comes on only sometimes, could it be the O2 sensor itself? Where should I look first? What would be the order of inspection in this case?

I have the DC 2003 Wrangler shop manual already. I do not have a Haynes or Chilton on this jeep yet.

If it is running lean that means that it is actually trying to compensate for this by sucking in more gas. Right? That could explain the low mpg?

Thanks for any help you guys can give me...

Jerry Bransford 06-23-2013 10:30 AM

My bet is a bad 02 sensor, which is what that code is indicating. I'd take it back & have them take care of it... and yep, I'd bet that bad 02 sensor is causing the engine computer to compensate by making the air/fuel mixture too rich now.

Holton345 06-23-2013 10:44 AM

I cannot take it back. It is a ten hour roundtrip drive. I will just fix it myself. Do you happen to know the part number for this on a 2003 Sport? And is it difficult to replace it at home? I have had these fail on cars that it was so simple to get to, and once on one that took a shop to do the job. I am a complete novice with the 4.0L. My nine years of experience has been exclusively on the 2.4L, unfortunately...


Okay, looking at I see four of them. With the engine being an '03 and having 141K on the odo, would it be worth it to change all four or would that be a waste of money? If I only need to do the one (meaning that they do not fail a lot at this mileage point) then how do I fine out which one is at fault? I would be happy with all new ones but will have to do them two at a time due to the cost.

Or am I reading this wrong, that it actually has one and that I need to see which one of the four my block uses? I am confused on this point.

pre-cat 1-3
pre-cat 4-6
post-cat 1-3
post-cat 4-6


Holton345 06-23-2013 10:55 AM

Also, is it okay to drive it until I sort this, Jerry? It seems that it would be but that I will be spending a lot more on gas until it is fixed. Will driving it damage anything?

Holton345 06-25-2013 10:27 AM

Followup post —

Okay, got the heep to the dealership, which is the only one I have ever trusted. (I have been a customer for ten years now, so even the older mechanics know me by sight.)

They were laughing at my rig because I had them swap the wheels off my 2003 Sport with my dead 2003 SE (31x10.5s on stock Eco rims versus 33x12.5s on MT Classic Locks). It has a small lift and Rough Country flares, so the smaller wheels with the stock backspacing look pretty silly. But the 33" MUDs are not safe to drive on and the SE ain't going anywhere with no motor. I swapped to see if the ride issues were all tire related or something else.


They are replacing both O2 sensors. The main one is going out and I decided to have them do the PITA downstream one while they had it in the bay. Get this: all six plugs had just about zero electrode left, and the nubs were almost totally rounded. The gaps were HUGE, like comically so. They were betting they could be the originals or the second set. It has 141K+ on the odo.

I asked about a general tuneup, but everything else is fine. There are no wires, but coil packs. I thought the 2003 still used a cap, rotor and wires. Whatever. What is there is solid.

So, new O2 sensors, plugs and (soon) new 33x10.5 DuraTracs on black 15x8 steelies and the MPG ought to come back up dorm my dismal 13.9 — Yes?

I included a photo of my dead SE on its final run right after the rod broke through the block. RIP, old friend. You will have a Chevy 350 one day...

Later, y'all...


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