'05 xA Relentless Check Engine Light

I have taken excellent care of my '05 xA. It has on 43K miles on it. The CEL came on a few months ago. I have an OBD code reader and the code is always the same - P0171. After a little research I learned that this is a "mixture too lean" code. Since the computer controls the mixture, there didn't seem to be much I could do. The car runs perfectly however the light is driving me crazy. I later had it hooked it up to a diagnostics computer and it said that the pre cat O2 sensor is the culprit. This had to be special ordered from the manufacturer. So, six weeks and $100 later I replace the pre cat O2 sensor. The CEL still comes on when the car warms up. More research told me that this is a common problem on earlier model Corollas. It seems that the Mass Air Flow Sensor can gunk up and also cause this error code. Since both cars use the same MAF I decided that this could be the culprit. I removed the MAF and soaked in 70% rubbing alcohol for about 45 minutes and let it air dry for an hour and put it back in the car per instructions I found on the web. Even though this remedy solved the problem with numerous Corolla owners and they swore by it, it did me no good. The CEL still illuminates when the car warms up. I am unemployed and I can't really afford to check the car into the shop and let them replace sensors, valves, egrs or converters at my expense in a shotgun attempt to diagnose this issue. At least this is my fear as to what will happen.



If anyone may have had this issue and resolved it or may know of a possible solution that I may have overlooked I would appreciate a reply.



There have been no major mods to this car. The only thing Ive done to the engine is install a K&N air filter.



Thanks to all who can shed light (no pun intended) on this issue.



Cheers,



mdhyre

Kennesaw, GA

Reply 1 : '05 xA Relentless Check Engine Light

I'd guess that you've damaged the MAF as the K&N air filter's oil tends to do that. I could be wrong but that would be my guess.



:::edit:::

This is what I've "seen" in a repair manual...



P0171



DTC Detection Conditions



With warm engine and stable air−fuel ratio feedback, fuel trim

considerably in error to lean side

(2 trip detection logic)





Trouble Areas



Air induction system

Injector blockage

Mass Air Flow (MAF) meter

Engine Coolant Temperature (ECT) sensor

Fuel pressure

Gas leakage from exhaust system

Open or short in HO2 sensor (bank 1 sensor 1) circuit

HO2 sensor (bank 1 sensor 1)

HO2 sensor heater (bank 1 sensor 1)

EFI relay

PCV valve and hose

PCV hose connections

ECM

Reply 2 : '05 xA Relentless Check Engine Light

Thanks HatenFate. I had run across that in another forum. I guess it will cost me $90 to tell for sure.

Reply 3 : '05 xA Relentless Check Engine Light

I think I have found the reason for the CEL. I installed a Rostra Cruise control unit on my car and noticed that the engine was idling way too fast. I compensated by adjusting the idle down to 500 RPM. The car ran fine and I thought I'd also be saving gas at the stoplights. I guess the ECM didn't like that. When I turned it back up to 750 RPM (where it belongs) the light has not come back on since. I'm lucky. It only cost me $90 for a new O2 sensor. It could have been worse. How sensitive cars are these days. One little tweak can throw a monkey wrench into the whole works. Times have changed!

Reply 4 : '05 xA Relentless Check Engine Light

Yeah, I would never mess with a factory set idle postion unless you were doing so for performance reasons, and knew how to program a fuel map. Running lean is a very dangerous thing to have happen and could potentially burn up the engine internals (i.e. pistons, valves).

Reply 5 : '05 xA Relentless Check Engine Light

Six days of city driving and no CEL. I think we've found it.

Reply 6 : '05 xA Relentless Check Engine Light

Good to hear.....let us know if it comes back.