Check Engine Light

[RyanM]

I'm new, so I'm not sure this is the place for a question like this; please let me know if it isn't.

My check engine light came on last night, and I checked the gas cap to see if it was loose-- it wasn't too loose, but it wasn't as tight as it gets either. I screwed it back down, and the light eventually went off later that night.

This morning the light came back on. I took it to a shop, and they told me the code the came up and reset the light but said to wait and see if it comes on again before doing anything about it.

The code is: "P0121 System Too Lean BNK 1"

Does anybody know what that means? I don't want to drive it (2006 tc) if it isn't safe...

Thanks!

[Redneck4csa]

I don't know, but I wouldn't want to drive it if it was running lean...

[chyz-dad]

the code is usually associated with TPS (throttle position switch) atleast from my past experience on other vehicles....never had a prob with my tC (YET....knocking on wood now)
With it running lean it may be something as simple as a clogged fuel filter...you can check that and/or replace it...but but as they all say why replace it if it's not broken....Navy is the brains when it comes to practically anything on this car..so if you want you can wait and see what he says...

[SquallLHeart]

first step for my troubleshooting procedure is to ask..

what was the last thing you did to your car? (that might've caused this)
or even.. last thing you didn't do?

fyi, for the gas cap... at least 1 click.. at least... 3 would be great.

[RyanM]

The last thing I did before it came on... I can't think of anything I did differently...

After I tightened the gas cap, the light went off later that night after I'd been in and out of the car driving about three times. It came back on in the morning, then off later in the day, and the same thing happened the day after that.

The light is on right now, but I just got gas and tightened the cap, so I'm wondering if it will turn off again after a few trips in the car...

Thanks for the replies!

[Htownrs5.0]

whats the mileage of the car?

EDIT*


wow didnt see the whole msg.. sorry for opening my mouth lol....

what type of gas were you using? ( meaning from what station ) when i lived in norfolk, va the station to avoid was crown gas station.. major issues with the dirty/watered gas...

[RyanM]

I'm using regular unleaded, and now that I think about it, I have heard from one other person that they had trouble with the station I filled up at before this happened.

I've filled up again since then, and the light is still on (it came back on yesterday after going off the night before...).

I wish Toyota had a resource to let us know that all these codes meant...

Thanks for the help everybody!

[Htownrs5.0]

its quite possible it is a dirty fuel filter.. like noted from anothers response earlier but it usual doesnt happen quickly takes quite a few fillups unless your gas station is from the 1950's lol

on a lighter note i just got back from the dealer and put my 500 bucks down for the rs5.0 woohoo very excited am I

[navylife59]

There seems to be a misnomer about your posted DTC "P0121 System Too Lean BNK 1". To be correct from the Scion Manual it should read this way:
P0121 Electronic Throttle Control System (ETCS)
and
P0171 System Too Lean (Bank 1)


Do you have an aftermarket header and/or s-pipe? What about an aftermarket intake? Are you running a 02 Simulator or have a wide-band gauge added to your system? These are known to cause P0171. I could see bad (contaminated) gas being a possibility. After a complete tankful has been run through the car since the bad gas, have Autozone or somebody reset the ECM for any DTC's.

DESCRIPTION
The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim consists of both the short-term and long-term fuel trims.
The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at stoichiometric levels. The signal from the Air-Fuel Ratio (A/F) sensor indicates whether the air-fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air-fuel ratio is rich and an increase in the fuel injection volume if it is lean.
Factors such as individual engine differences, wear over time and changes in operating environment cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short term fuel trim compensation. If both the short-term and long-term fuel trims are lean or rich beyond predetermined values, it is
interpreted as a malfunction, and the ECM illuminates the MIL and sets a DTC.

Listed below are possible trouble areas for P0171:
1. Air induction system
2. Injector blockage
3. MAF meter
4. ECT sensor
5. Fuel pressure
6. Gas leakage from exhaust system
7. Open or short in A/F sensor (sensor 1) circuit
8. A/F sensor (sensor 1)
9. A/F sensor heater (sensor 1)
10. EFI relay
11. A/F sensor heater and EFI relay circuits
12. PCV hose connections
13. PCV valve and hose
14. ECM

HINT:
• When DTC P0171 is set, the actual air-fuel ratio is on the lean side. When DTC P0172 is set, the actual air-fuel ratio is on the rich side.
• If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 may be set. The MIL is then illuminated.
• When the total of the short-term and long-term fuel trim values is within the malfunction threshold (and the engine coolant temperature is more than 75°C [167°F]), the system is functioning normally.

P0121 can cause the car to go into Failsafe Mode aka "Limp Mode". Does your car drive erratic? You will know this for sure if it were to ever happen.[/COLOR]

ECM cuts off throttle actuator current and throttle valve returned to 6.5° throttle position by return spring. ECM then adjusts engine output by controlling fuel injection (intermittent fuel-cut) and ignition timing in accordance with accelerator pedal opening angle, to allow vehicle to continue at minimal speed.*

HINT:
*: The vehicle can be driven slowly when the accelerator
pedal is depressed firmly and slowly. If the accelerator pedal
is depressed quickly, the vehicle may speed up and slow
down erratically.

[RyanM]

Thanks for that information-- I've run through about two tanks since this happened, and the light has been going off but coming back on the next day-- it has happened twice that it will be off in the evening and come back the next morning.

I'll take it to AutoZone and have them re-set it and see what happens.

I'm not using any aftermarket products-- everything is just how we bought it.

Thanks!

[RyanM]

I just realized that I haven't replaced the air filter in a while-- probably in 4 or 5 oil changes-- could this be causing the problem? I'll go in the morning and replace it and see what happens...

[Htownrs5.0]

i 20k miles... its possible but i personally couldn't see it happening unles you drove through some sandstorms in the middle east ... but thats just MO cya gotta get to work lol

[navylife59]

That should make it run rich. Autozone can tell you if there are any pending codes as well. Since you have no aftermarket products and it appears that your Powertrain warranty is still available,I would take to the Dealership. Change that airfilter first and see where that gets you before you go there. Improper maintenance will cause this to be a non-warranty issue if they see a dirty filter.

[RyanM]

Ok thanks!

[navylife59]

Let us know how it turns out.