Hello everyone! I have a 2000 Dodge Stratus with a 2.4L 4-cylinder engine and about 146,000 miles on it. About 4,000 miles ago, the check engine light came on. When put on the scanner, an engine code of PO171 (lean fuel condition) appeared.

After clearing this code, a few weeks later, again the engine code PO171 appeared. I changed the front (Bank 1) oxygen sensor and the check engine light stayed off. The oxygen sensor was the original. The only difference I noticed was a drop in fuel economy.

A few weeks later, the car began running very rough and misfiring, you could hear it through the exhaust and there was a total lack of power. The check engine light came on and this time in addition to the engine code PO171, PO301 (random misfire - cylinder 1) was also displayed. I switched cylinder 1's spark plug with the one in cylinder 2 and received engine code PO302 (random misfire - cylinder 2) which led me to think it was the spark plugs. I put new spark plugs in the car along with spark plug wires and thought my problems were solved.

Over the past months, I've continued to receive the engine code PO171 inconsistently. What I have noticed is that the only time
the engine code PO171 appears is when the car is locked in gear climbing a hill or when you have to get out into traffic and really step on the gas pedal. Other than these two instances, the check engine light does not appear. I'm stumped!

Since, I have had the car smoked to check for vacuum leaks. The fuel injectors sound fine and the fuel pressure is fine. The fuel pump is only about 50,000 miles old too. I've checked the exhaust and cannot find any openings where a leak may be present. I've read the other postings, looked into some of the things suggested without solution. If anyone has any ideas, your input would be greatly appreciated.

 

could be a bad 02 sensor have read several posts last few years where new sensor goes bad very quickly ,bad wiring to 02 sensor, have you checked pcv valve ,air filter ,and MAF(mass air flow sensor) may be dirty or bad

 

It's very possible for cheaper sensors to go bad all the time, the dealer is the only place to be 100% sure you have the correct part but it's expensive.

If you get a scan tool hooked up that reads the upstream bank 1 sensor 1 trim levels then you'd get a good idea where to start. Higher positive fuel trim readings usually mean there's a vacuum leak somewhere so the computer is trying to add more fuel, or it could also be faulty readings from the new sensor.

 

Thank you for the advice and suggestions you have offered. I changed out the PCV valve on my vehicle which made it run much smoother at idle. I also replaced the aftermarket oxygen sensor with a factory oxygen sensor and put in a new air filter. Despite these changes, the PO171 engine code still appears.

The engine code (PO171) still only appears when the engine is under load, either getting out into traffic (heavily stomping on the gas pedal), when going up a hill (one in particular) or at highway speeds (>70 mph - intermittent). If I use the cruise control, which I have been doing as an experiment, engine code does not appear. As soon as I go back to manually operating the gas pedal, especially on this one hill, the engine light appears.

I did hook up my vehicle to a Scantool and monitored its fuel trims values but they seem to jump all over. Is this what they are supposed to do? I'd say the values are split nearly 50/50, 50% negative and 50% positive. Any advice as before is welcomed.

LTFTRM1:

- @1500 rpm = 10.9
- @2000 rpm = 10.9
- @2500 rpm = 3.9

STFTRM1:

- @1500 rpm = -7.8 to 3.9
- @2000 rpm = - 7.0 to 0.8 (0.0 and 0.8 show up most often)
- @2500 rpm = -4.7 to 3.9

STFTRMII:

- @1500 rpm = -2.3 to 6.3
- @2000 rpm = 0.0 to 7.8
- @2500 rpm = -4.7 to 3.1

 

Short term upstream fuel trims will always vary, it's how the PCM monitors cat performance.

Assuming that your readings are in percents, the long term does look very high. Zero is ideal but when it's showing 10%+ fuel trims that means the computer is detectings a lean condition from the O2 sensors and is adding more fuel. Your MPG will suffer greatly from that too.

Usually vacuum leaks are the #1 cause of lean conditions. Also if you haven't already, reset your computer by disconnecting the negative battery cable for a little while. It could be possible that your old PCV valve was causing a big vacuum leak and the fuel trims haven't adjusted to the new one yet.

 

Thank you for the feedback. Before I installed the aftermarket oxygen sensor, I was getting 27 mpg even with the "lean condition" (PO171). After, 22 mpg but the car idled much smoother. Installing the new PCV valve helped even more.

Hopefully these repairs along with the new factory oxygen sensor will remedy my problems. I'll definitely disconnect the battery to reset the computer. And if that doesn't work, then I'll look again for a vacuum leak as you have suggested. Thank you!

 

Since installing the new (factory) oxygen sensor, new PCV valve and disconnecting the battery to reset the car's computer, my check engine light has stayed off. I've driven just over 500 miles since and so far, so good. I've even seen a slight improvement in my gas mileage since. So I thank those of you whom supplied me with your advice and knowledge. Thanks again!

 

Good to see that your problem went away. I would like to add one more thing to check, and that is the snorkel between your MAF and your throttle. If there is a hole in the snorkel "false air" can enter the intake behind the MAF and not be accounted for by the PCM. Because the PCM bases its fuel injection on the MAF input, any additional air reaching intake would cause a lean condition during combustion, which in turn would be detected by O2 sensor in exhaust.

 

So here I am again, looking for advice as to why my 2000 Dodge Stratus SE continues to throw the engine code PO171. As in the past, this code is intermittent. The advice previously provided has been applied without success.

As in my past posts, my vehicle continues to code on this one hill in particular while at highway cruising speed (55 mph). The vehicle usually makes it almost to the very top of the hill before throwing the PO171 engine code. The code does not come on when the cruise control is engaged.

In addition to this one hill in particular, there two entrance ramps on which my vehicle also throws the PO171 engine code. Again, the vehicle makes it almost to the top of the hills associated with these two entrance ramps before coding. Usually the vehicle codes just before the car shifts and the entrance ramp begins to level out.

Another thing I have noticed and associate with the throwing of the PO171 engine code is the rough idle of my vehicle. In general, my vehicle has a relatively smooth idle but occasionally upon starting has a very rough idle. Usually when the vehicle is started up and the rough idle is present, the PO171 engine code is not far behind, but only under situations that require the engine to be under load (ex: having to stomp on the gas to get out into traffic or going up a moderate to major hill).

Another thing I have noticed is that when the vehicle is started and the rough idle is present, the car lacks power. You can floor the car and its almost as if the added fuel still is not enough to bring the vehicle up to speed quickly. When the idle is smooth, the car still has a powerful take off and you can even spin the tires.

If anyone has any additional advice, I appreciate it.

 

You may want to have cylinders compression leak tested, my 2000 has a cylinder random misfire, I have replaced everything in the system. O2 sensor, map sensor, air intake temp sensor, coil pack, wires, plugs and egr valve. I asked a mechanic and he believes that I have a intake or exhaust valve spring or valve bad. They can develop holes from poor fuel quality. Have a reputable mechanic test it. And good luck.