My 4.7L 2000 Durango is throwing a P0171 code (Fuel Trim, Bank 1, System Too Lean). Mileage sucks (~8 MPG), idles rough, and seems to miss on letting off the throttle. It also is belching soot out the tail pipe. I left it idleing in the drive way for 5 minutes and I now have a large black spot on my driveway directly under the tail pipe.

I suspect that it's probably the front O2 sensor but, if it were the O2 sensor wouldn't I get some kind of error code for a bad sensor? Something like under or over voltage for the sensor? I've read a couple other posts where replacing the sensor worked, but they didn't say anything about getting another code for a bad sensor.

Thx
-K2

 

I work on Lexus', (besides my CarPC biz) but on ours, when we have a P0171, we replace the MAF sensor.
Maybe you can check some readings with a scan tool first. Also, clear the code and see which code returns.
Please post your findings.

 

As the code states, the sensor is detecting a lean condition on one bank of cylinders. A actual bad sensor will set a different code. This could be and probably is a vacuum/air leak or injector problems. Pop the hood and listen for any abnormal air hissing, disconnected vacuum hoses, possible broke pcv valve. Dodge uses a MAP (air pressure) sensor rather than airflow sensor so no easy way to check that. If this finds nothing then time for a shop to have a look see.

 

CarputerGeek and buckw1 -

Thanks for the tips. I'd already replaced the front O2 sensor though before I read these replies. The engine is running much better now, 16-18 MPG in town (which it has NEVER done in the almost 6 years I've owned it), no more rough idleing, and doesn't hesitate on letting off the gas. It's still thowing the P0171 and P0155 codes when I use the "on - off - on - off - leave it on" method of reading codes. I'm sure it's just showing me whats stored so the new O2 sensor may have cleared the P0171. I need to find a way to clear the stored codes.

I will however go check for vaccum leaks.

Any recommendations on a software based scan tool? I have a 99 VW Passat and have VAG-COM for that but I guess its time to break down and get something for the D.

Thx
-K2

 

I've reset my car's ECU by disconnecting the power from the battery and let it sit for a few minutes...I usually took a smoke break at this time and then reconnect power. You can try that and your CEL should go away, if not the dealership or a local garage should have a 'puter to reset the ECU with.

 

I actually went over to Advanced Auto Parts this evening and they had a code reader that you could borrow. I used it to clear the codes.

Now it's like being a cancer patient - although the symptoms are gone, you have to wait awhile before you can be declared "cured".

-K2

 

If you still are having a problem with your Durango, maybe your problem is the same as mine, as follows:

My 2000 Durango SLT with a 4.7L engine has failing (front) O2 sensor. 91,000 Miles. Replaced OEM o2 front sensor.

Repeated code being picked up: PO171 Fuel System Lean - Engine Light On.

The dealership did perform diagnostic checks on all possible problems - associated with the above code, but found all items to be OK.

Their conclusion is that the power steering switch is leaking fluid, pushing oil into the harness. Dealership states that the o2 sensors and the power steering switch wires are running in the same harness. The faulty switch and their related wires are interfering with the signal picked up from the o2 sensors - and providing faulty information back to the computer.

Their recommendation was to replace the faulty power steering switch, both o2 sensors, and take apart the wiring harness and create another individual harness just for the o2 sensors. No more cross 'talking' between sensors. Stated the o2 sensor is good just reading low voltage.

After my dealership noted the above, I researched the Internet and came across the following identical problem but with a different solution. Please see / read the top of the second page: ttp://www.wellsmfgcorp.com/counterpoints/counterp_v9_i1_2005_2.pdf

The dealership requested a hefty sum to correct my problem. I have paid for their diagnostic service and will repair the Durango myself, but after reading the Well's article, I question which solution is correct.

Dealership did contact their Tech Line, and either created a case number, or from previous similar situations - Case #8314819.

Today, I received my ordered power steering switch and replaced it. Prior to replacing it, I sprayed Brake Cleaner into the power steering switch connector and left it uncoupled for a couple of days. The item did leak fluid through the electrical coupler.

Put the new power steering switch in and put it on a scanner to have the 'check engine' light to go off. During this check, the o2 sensor was reading zero. I went back to the dealer, who accepted that the sensor was not reading, and again stated that the wires have to be cut and spliced with new wires, plus noted harness back to computer.

Has anyone else had this problem?

Does anyone have electrical diagrams for this vehicle to identify what the o2 sensors couple to - in order to splice new wires?

I look forward to all responses!

 

You can pull the wire loom back and follow the wires. Fluids can do that to the 02 sensor though, I know that from experience. I had oil on the end of my rear downstream o2 harness and it kept throwning up a CEL, the oil itself wasn't causing the CEL, but the oil kept grounding out the voltage instead of going to the ECU.
My question is, why would they have to replace the wires instead of just peeling back the wire loom, seperating the two sets of system wiring, clean them (electrical contact cleaner), re-inspect them, then reloom. I also don't understand why they would have to replace the entire wiring harness going to the ECU either. Sounds like a lot of unnecessary work to me!
I say, get a second opinion from an independent garage. Joe Dirte' can get it done for less and may have a better solution...just let them know what you've been told and go from there. The more I re-read, the more suspicious I get about the whole harness thing....
It's obiviously not under warranty anymore and someone needs money

 

Durangofan -

That was my problem. After I replaced the O2 sensor, I still had the same problem. Then I found the same article you did. I ended up replacing my power steering pressure switch ($25), dumping a can of electronics cleaner down the wiring harness over the course of a four day weekend, leaving the O2 sensor disconnected, and letting it sit. Hooked it up Sunday, cleared the code and it lasted 24 hours. I just drove it like that figuring it would take time for the power steering fluid to wick out of the harness. In about a week it suddenly started running better - no rough idle, better gas mileage. Cleared the code again and it's been off for two-plus weeks now.

Don't think there is any need to replace/rebuild the wiring harness. Let it dry out and see what happens.

-K2

 

Thanks KTwo for your response via e-mail.

I have sprayed about 15 cans of brake cleaner through the various harness that run down behind the engine - which one of them should lead to the o2 sensor leads.

Thus far, I keep clearing the codes by disconnecting the battery.

To date, the check engine light comes back on after several miles.

I just sprayed another couple of cans of brake cleaner - into the wires of the harness(s), hoping to clear the power steering fluid out of them. I reset the computer.

We'll see how long this lasts.

K-Two - which harness did you dump electronics cleaner down or into?

I look forward to your response.