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Discussion Starter #1
Okay, here is what's happening. I got a PO174 code, I think, back at the end of July, changed driver's O2 and problem solved. Light gone didn't come back. About two weeks ago my light came back on, PO174 code, changed O2 and it was gone. Now yesterday my light came back on, PO174 once again. My car has 154K on it and just last Saturday my dad ran two cans of seafoam through it, trying to do me a favor after I decided against it and to go with auto-rx from Mager Thom's suggestions. Car seems to idle fine, little high at first, but settles down after a few seconds.
I've seen the lists of possible causes, but I don't even know where I should start.
HO2S-11 = DTCs P1130, P1131, P1132, P0171 and P0172
HO2S-21 = DTCs P1150, P1151, P1152, P0174 and P0175
Possible causes:

Fuel System

Excessive fuel pressure.
Leaking fuel injector(s).
Leaking fuel pressure regulator.
Low fuel pressure.
Plugged injector(s).
Damaged/disconnected HO2S circuit.
Induction System

Air leaks after MAF.
Vacuum leaks.
Restricted air inlet.
PCV system.
Base Engine

Oil overfill.
Cam timing.
Compression.
Ignition

Coil and secondary side of ignition system.
Check air intake for leaks, obstructions, and damage.
Check air filter, air filter housing for blockage.
Check positive crankcase ventilation system integrity.
Check engine vacuum integrity.
HA41 DTCs P0172, P0174, P0171 AND P0175: FUEL SYSTEM AT THE CORRECTED FUEL TRIM

Diagnostic Trouble Codes (DTCs) P0171 bank 1 (Cylinder 1) and DTC P0174 bank 2 indicate the fuel/air ratio is too lean. The fuel trim system is at the rich correction limit.

DTC P0172 bank 1 and DTC P0175 bank 2 indicate the fuel/air ratio is too rich. The fuel trim system is at the lean correction limit.

HO2S DTCs Reference list:

-- HO2S-11 = DTCs P0171 and P0172
-- HO2S-21 = DTCs P0174 and P0175

Possible causes:
Fuel system
-- Excessive fuel pressure.
-- Leaking fuel injector(s).
-- High fuel pressure.
-- Low fuel pressure.
-- Contaminated fuel injector(s)
Ignition system
-- Spark plugs.
-- Spark plug wires.
-- Coils.
Induction system
-- Air leaks after the MAF sensor assembly.
-- Vacuum leaks.
-- Restricted air inlet.
-- PCV system.
-- Improperly seated engine oil dipstick.
Base engine
-- Oil overfill.
-- Cam timing.
-- Cylinder compression.
-- Exhaust leaks before or near the HO2S(s).
l Check intake air system for leaks, obstructions and damage.
l Check air cleaner element, air cleaner housing for blockage.
l Verify fuel level.
l Verify integrity of the PCV system.
l Check for disconnected spark plug wires.
l Check for vacuum leaks.
l Verify customer did not run out of fuel.
Those are two different posts I've found. I think I have a drivers exhaust leak, one says it is a cause and one doesn't. Are both lists correct? Where should I start? I'm gonna clean my MAF again, even though two weeks ago it was clean, guess it can't hurt. Thanks for the info and sorry bout the super long post.
David
 

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Double check ALL grounds, especially those in the wiring harness. If you have tech manuals, they will show the locations of all grounds.
 

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I take it you hear no vacuum leaks anywhere? If MAF is clean, and the code returns, it's possible the MAF is faulty.

You may want to consider biting the bullet, and have a dealership service center perform their diagnostics. The pinpoint procedure for this code is rather detailed and lengthy, especially in testing fuel pressure, and part of the routine is based on KOER (Key On, Engine Running) test (or code readings). Their diagnostics should tell you exactly what's wrong. Have them detail it, and go complete the work yourself.
 

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clean your iac......some people have stated it iac related.....and cleaning it isnt very hard.....you just have to be careful when you take it out...just do the free things 1st....check your maf wires....its either maf or iac related.....or its the harness like johnaec said
 

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Discussion Starter #5
Okay, well I didn't clean my MAF cause I was too busy eating and what not on lunch and didn't want to do it when I got home with it hot. So I am gonna do it in the morning. I checked for leaks on the intake and everything and I couldn't hear any. I did hear my injectors clicking quite loudly in park at idle. A local Valvoline place cleans 'em for $40, so I think I'll have them cleaned as soon as I can afford it. Also, about the IAC, where exactly is it? Is it that piece at the back of the engine on driver's side? I'll try and check that and at the wiring in the morning as well. Thanks much ya'll!!!
David
 

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"Damaged/disconnected HO2S circuit"

Seems suspicious that code came up right after using that Seafoam.....

I just hope that your sensor is not contaminated or "coated" in some way
as the result of running that stuff through......

IronChopz suggestion about a diagnosis makes good sense.....I'm just
not sure the logic tree addresses what may have happened...I hope it does...
 

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thumpin_tbird:

I know this may be unrelated to your seafoam issue, but i had a PO174 on a 94 XR7 that i cleared.

Please check your PCV hoses, especially if you have 2 vacuum lines going to the PCV. If you do have 2 lines, thoroughly check the smaller vacuum line that has the elbow. Mine was very soft and oily, and had a slit in the elbow area that you'd never see unless you squeezed it.

A vacuum leak isn't always audible as a hissing noise...it may be leaking vacuum but you can't hear it. I replaced the line and said good bye to the Check Engine Light.

Just my 2¢

-hooD :zspot:
 

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Discussion Starter #8
Okay, I finally cleaned my MAF, but it was just now and I'm at work. I did it 2 hours after I got to work, and letting my computer reset. Drove a 180 mile roundtrip last nite to go trick or treating with my daughter and, my car ran fine. But when I went to the garage to start my car, it died. It did this a couple of times, then I revved it up and it stayed goin and had to quickly put it in reverse to go. Died when I went to shift to drive, started it in nuetral and put it in drive to go. In between these times, the idle seemed to be getting higher on each restart, and listened to it after starting it and stayed at a low idle in park, I could hear a hissing right back by the throttle body closer to the driver's side. I'm not sure if this was just the airflow thru the intake or not. Didn't really sound like regular airflow, but not positive. The first stop sign was a little over a mile down the road and I just coasted through it. Next one was about 10 miles away from home and it was fine then. No more problems with dieing after leaving my driveway. After work I'll check it out more, I ordered an IAC from O'reilly's. I am still not sure where exactly the IAC is, I've searched the forums and looked at my Haynes manual and don't see anything about the location of it. Thanks again!!!!
David
 

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I'd hold off on the injector cleaning 'til you've checked all the other items, clicking
injectors are normal.

I'm not sure how you're resetting your EEC, but letting it sit doesn't do anything.
Pull your #15 fuse and start your car (it won't) a couple of times...that will drain
all stored energy away from the EEC and it will loose memory......you can then
replace the fuse and start the car with the air on and idle 'til warm, then drive for
20 minutes or so...the computer will have learned enough to work fairly well and
will continue to learn and adjust itself continuously from then on.

Per hooD's suggestion: check all your vaccuum lines....also the small diameter
one that runs to your purge solenoid.....if it has ever been replaced with tubing
that is not fuel resistant...it may well have gone soft and could be leaking.
 

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Discussion Starter #10
I disconnected the battery cause I always forget the fuse number. I will do a more thorough inspection of the hoses tonite. Where is the purge solenoid, I'm not sure if it's in my haynes manual as its at home. Thanks, I swear I'm going to kill my dad!!!!!
David
 

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It's on the Evap Cannister....front passenger side corner of the
engine compartment, down low........
 
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