I keep getting a p0171 code (lean bank 1) on my 96 Neon. I've changed the air filter and the O2 sensor and I've checked for vacuum leaks, but the CEL keeps coming back on, giving me the same code. It hesitates and surges a bit at cruising speeds and my gas mileage is terrible! What else could it be?

Karl918

 

fuel filter, coolant temp sensor, map sensor... a number of things really but of course if the other sensors are bad they should be throwing a code for them also... could be low fuel pressure either weak pump or weak regulator, could have a bad or weak injector(s), could have bad injector orings...

 

It seems to have plenty of pick-up....wouldn't a weak fuel pump or clogged fuel filter or bad injector effect that? I did put some Lucus fuel injector cleaner in the tank...maybe that'll do it. But answer this....if I don't clear the code, will the symptoms continue?

 

When the car is idling, (and it idles fine by the way) the Fuel Trim is right where it is supposed to be, but as soon as I give it some gas the ST Trim quickly goes up to +24.2% and stays there.

I also checked the TPS, its fine. I replaced the pcv, and cleared the code, but soon the check engine light came back on. p0171. I even unplugged the MAP/IAT Sensor....no change in the readings. I was suprised the car started to be honest.

Anybody have any ideas?

 

well all those things being bad would deff affect performance but if its only starting to go bad then its only going to be bad enough to limit your fuel flow so you get the code but not bad enough to hurt performance... if it was one of the sensor acting up you would have a code for that sensor or should... but it wouldn't hurt to get the fuel pressure checked which would tell you if the pump or the regulator was the problem... that would be a good place to start... as far as what to do from there... its hard to say...

 

Im still monkeying around with this. So Ive checked for vacuum leaks, replaced O2 Sensor, the MAP/IAT Sensor, the PCV valve, and the code still came back. So I got a ECU out of a '97 and the code went away but I got a new code 1491 (MIL 35) which is a problem with the radiator fan/s. They don't turn on. So I got another ECU, this time out of a 98.....got the same code! Spooky huh?

Is there something about the ECU's not being the same year as my 96? Can it be re-flashed?

By the way, when I pulled the original ECU, one of the connectors was full of oil! Appearently the Oil Sending Unit went bad and oil traveled up the wire to the ECU which I assume created the original p0171 code. I cleaned all the connections and replaced the Oil Sending Unit (which I think Chrysler calls Low Oil Pressure Sensor). It was a bit of a pain to replace because it didn't quite fit into the special socket made for it. I had to file the sides to get it to fit in the socket. I saw another at the junk yard with the same issue.

 

i would look at the intake gaskets they could be leaking or your throttle body gasket is leaking.

 

Thanks ScottyP. but I don't think its the intake gaskets because, just for giggles, I put the old ECU back in and I only got the original p0171 code....and not the 1491. Someone told me a little while ago that the (newer) ECU is probably fine but needs to be re-programmed for my car. Do you (or anyone) know whats involved and about what that costs?

Karl918

 

man i have the same problem as you mentioned with my 96 neon
i havent been through everything you have though
but it does exactly what you complained about
im getting 14 mpg as well!
all ive done is changed the plugs and wires
i was thinking it was the oxygen sensor
so i was doing my research and it lead me to this post
how should i go about my problems?

 

The problem was the oil sending unit was actually sending oil up thru the wire (yes thru the wire) were it eventually made its way to the ECM. The oil was puddling up were the wires all plug into the ECM and that's what caused all the problems. I replaced the oil sending unit and the ECM. I took apart and cleaned the hub were all the wires come together, as well as the connection at the oil sending unit and the problem went away! Stupid problem that was easy to solve. I bet if you pull the connections on your ECM you will find oil. Appearently the problem is fairly common...I went to "salvage" yard to see if I could get a ECM and found a couple 96's with same problem, so be carefull if are planning to do the same. The units have to be identical...same year, same numbers. Also, my 96 has California Emissions, which is rare on the east coast, so I ended up buying a refurbished one from Solo Auto Computers in Florida. They take your VIN number and the mileage and program the info into the ECM so there are no issues. Bought it online and had it in a couple days. The oil sending was less than $10, the ECM was about $250, and a can of electric wire cleaner is about $7. Most of the repair time went to cleaning the connections. Good luck!