Sc5Speed

Hello I have 2 codes showing on a 2001 RX 300 that has 62,000 miles. The Trac off light, SVC and Check Engine light are on, when I check it at Auto Zone they show both 0171 and 0174 codes, I have looked for past threads and can not seem to match these 2 codes together to know what the problem really is, anyone know what it means when these 2 show at the same tim

Lexmex

Focus on the P0171 alone. Have you tried clearing the codes and they still come back?

Sc5Speed

Yup, they come back, I spoke with the guy who sold me it and he said he did not use Denso or Nipponese sensors when he replace them, could that be the problem?

Lexmex

Which sensors?

Sc5Speed

Upper and Lower Bank and he said he also replaced the cam sensor....

Lexmex

We've had members who used something other than Denso A/F sensors and wound up having issues.

iolmaster

iTrader: (1)

When I had problems with my A/F sensors I got specific codes that pointed directly to the sensor in question. I am getting the 0171 code now and all the research I have come up with points to the Mass air flow sensor, not the A/F sensors. All of my A/F and oxygen sensors were replaced with Denso. I have read nothing about 0171 pointing to A/F sensors. In fact a number of articles specifically say do not replace A/F sensors for that code. Please correct me if I am wrong since I am about to buy a mass air flow sensor.

Lexmex

I am referring solely to what he replaced (not the actual code).

The P0171 can potentially be a number of things and not even necessarily the MAF Sensor. A giveaway for me on a MAF an a P0171 is not having a P0171 pending, but rather just the P0171. I have had that occur during my earlier years in Mexico when the MAF got dirty as a result of the K&N oil from the filter.

The P0171 code can even be fuel injector blockage, something temporary with the quality/temperature of the incoming air (to the engine), a loose or broken hose, a gas cap issue. Bad fuel (although not a problem for most of us), was a problem for me in Mexico, and can clog up injector(s). It's very difficult code to pinpoint unless you have something like advanced OBD2 diagnostics (which I have) and are able to look at a freezeframe at the time the code came up to help pick off where the problem might be. A dirty IACV is one of the more frequent P0171 instigators I've seen in this forum over years.

Sc5Speed

Ok, Consider this..... When I bought the car it had a battery that the previous owner put oil on the terminals, he says he does this to every battery??? Also it was a Die Hard Gold and there was corrosion below the Battery, I replaced the battery.....Sooooo....would him putting oil on the Battery posts be causing me a problem and mess with the MAF or should I just replace the upper sensor see if that works and then replace the lower next? Thank you for considering this......

Lexmex

I had a Die Hard Gold once, not a bad battery at all.

Well, assuming you have cleaned the oil off, the condition would either clear op or not. The thing I'd really do is have someone with an advanced OBD2 scanner/diagnostics check the freezeframe information to see what fuel trims, etc., air flow, basically see what was out of whack at the time the code went off.

Nad1370

P0171(bank 1) and P0174(bank 2) ----System too Lean---
Possible causes:

 Air induction system
 Injector blockage
 Mass air flow meter
 Engine coolant temp. sensor
 Fuel pressure
 Gas leakage on exhaust system
 Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
 A/F sensor (bank 1, 2 sensor 1)
 ECM

Check for vaccum leaks in the intake side: hoses, plenum gasket, etc...
I would also suggest cleaning out your Mass Air Flow meter.
A dirty MAF could give wrong readings to the ECU.

Are you using quality gas?

Really need a scan tool that reads long/short term fuel trims to determine if your "fixes" changes the value.

Aprazur

Last week I changed the plugs. In the process I broke the old PVC valve off in the left rear cyl location. The rubber grommet was hard with age/heat (1999 112K). I was able to dig the old grommet and PVC parts out but did not have a new grommet to install the new PVC with. So...I put the PVC back in (loose) in the head and finished the plug job.

Long story...short. When I started it up it ran a little rough. I checked it with my code reader and got the P0171 reading. Hmmmm? Pvc hole sucking air?

I took the new PVC valve out and wrapped the base with several rounds of black electrical tape and tapped it snuggly back into the head. I started the engine and it ran smooth. I shut it off and erased the code. No problems since in the last week.

You might try looking for a vacuum leak? Just a wild *** guess. Good luck.

Jerry

Lexmex

Yep.

Open PVC holes on the manifold (passenger side) or on the air intake tube (driver's side) can cause the P0171.

Anyone who's seen my intake setup on page 6 of my cardomain page knows I run a very open intake. The PCV holes I just mentioned have been capped off (so that crankcase ventilation doesn't end up coating my intake with oil residue) and I'd say maybe every week to other week I get a P0171 that I end up clearing quickly with an OBD2 scanner, but sometimes I'll go weeks without an issue.

There are exhaust cracks that can occur underneath the engine and just off the manifolds close to where the A/F sensors are.

Sc5Speed

Hey Everyboby
Thank you for the help, Now get this....I changed the Bank 1 upper sensor and the little rectangle A/F curcuit , So after changing it and clearing it the Check Engine light the Trac Off and SCV lights come back on .So that was Friday evening and they were still on saturday, then sunday they went off, I was excited hoping the problem has been addressed, But nooooooo All 3 came on again this eveing after driving around alot today with them off....check engine, Trac off and SVC lights...any thoughts? is this some kind of short or???

Lexmex

When you say Bank 1, which sensor are you referring to?