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Old 08-23-2009, 03:16 PM   #1
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Default P0171 code with freeze frame data

Can any of you code guys tell me is it normal for your short term and long fuel fuel trim to be the same like this ? I know I don't have a lean tip in issue.

P0171 (lean)
Load valve 16.47%
Engine coolant temp 201.20 F
Short term fuel trim 14.84%
Long term fuel trim 14.84%
Engine RPM 2151 rpm
Speed 39.15 mph


Thanks in advance
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Old 08-23-2009, 03:26 PM   #2
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Could it be that 14.84% is the positive limit of the fuel trim? That's a pretty large figure, though I've never seen published data on what the limits actually are.

Try cleaning the MAF sensor. Pop it out, shoot some carburettor cleaner at the wire. Soak it good. Put it back, and monitor the realtime fuel trim.
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Old 08-23-2009, 03:55 PM   #3
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Thanks Joe,
I'll try that and recheck the live data.
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Old 08-23-2009, 04:08 PM   #4
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I just did a quick Googling and found out that they actually sell cans of MAF sensor cleaner: CRC Mass Air Flow Sensor Cleaner, 11 Wt Oz - CRC05110

Probably the same stuff that's in the carb cleaner can, buy you never know. See if they've got it at your FLAPS.
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Old 08-24-2009, 10:29 AM   #5
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Quote:
Originally Posted by Joe Perez View Post
I just did a quick Googling and found out that they actually sell cans of MAF sensor cleaner: CRC Mass Air Flow Sensor Cleaner, 11 Wt Oz - CRC05110

Probably the same stuff that's in the carb cleaner can, buy you never know. See if they've got it at your FLAPS.
I think carburetor cleaner contains an oily lubricant. You don't want any residue on the thin MAF, from what I understand. So, basically just use MAF cleaner, not carb cleaner and definitely not brake cleaner.
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Old 08-24-2009, 12:33 PM   #6
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I use brake cleaner, but they are not all the same so be careful. denatured alcohol is usually acceptable.

Lean codes can come from a variety of reasons, when you are done, you need to clear the code and testdrive trying to exactly duplicate the conditions when the code set. A few drive cycles may be required to set the code.

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Old 08-24-2009, 05:24 PM   #7
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Removed the MAF, sprayed it down with CRC MAF cleaner (let it dry), cleared the code so far it hasn't come back but now I got a P1170 code I'll give it a few days clear it and see what happens..........Thanks for the input.
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Old 08-24-2009, 05:41 PM   #8
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Hmm.

Your first code was for system too lean, and you had a huge positive fuel trim. When a narrowband O2 sensor degrades, its output voltage tends to decrease. A low output voltage, so long as there were occasional crossings above 0.45v, would be interpreted by the ECU as a valid lean signal, and thus the ECU would start pouring in more fuel until it gave up and threw the max trim code.

Now you've got a code saying that the forward O2 sensor isn't crossing at all. Starting to sound like a bad sensor.

If you want, you can try swapping the front and rear sensors first, to see if that restores normal operation. You might get a P1137 or something in the range of P0136 - P0140, and if so, that proves that the sensor itself was bad. (ie: the fault moved from Bank 1 Sensor 1 to Bank 1 Sensor 2 when you moved the sensor from one spot to the other.) Fortunately, while a bad sensor in position 2 will still fail you at smog check time, it won't cause you to run over-rich and endanger your cat.

On the plus side, O2 sensors are a hell of a lot cheaper than MAF sensors. A Bosch 4-wire universal should run maybe $40-$50 at the auto parts store.

Last edited by Joe Perez; 08-24-2009 at 06:15 PM.
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Old 08-24-2009, 06:11 PM   #9
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I replaced the front 0/2 sensor two months ago, because I was running rich,
still ran rich untill I replaced the Barometric pressure sensor with a (used one) aka "boost sensor" maybe I should relocate the 0/2 sensor closer to my turbo outlet ? Its located next to my wideband 0/2 in front of the cat.......but then again its been like that for two years now. This code just started. ( don't have smog checks in VA.)
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Old 08-24-2009, 06:16 PM   #10
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You have a wideband?

Thanks for not sharing that earlier.

What sort of AFR does the wideband say you are at in normal, steady cruise?
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Old 08-24-2009, 06:25 PM   #11
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Sorry, just assumed everyone had one, A/F's at say 60 mph are high 13's to low 14's at idle 14's-15's
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Old 08-24-2009, 06:36 PM   #12
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So it sounds like you genuinely are running rich, despite the fact that the ECU is throwing codes and setting trims that tell us it believes you are stuck lean.

If you want to be triple-sure, use a voltmeter to measure the output of the NBO2 sensor. I'm guessing it never (or almost never) goes above 0.5v, even when you're at WOT.

Or just swap the sensors front to back. But this really sounds like a dead sensor (or maybe, just maybe, a dirty / corroded contact somewhere in the sensor's signal path).
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Old 08-24-2009, 08:26 PM   #13
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Joe, checked 0/2 voltages at idle 0.060,0.075 rev. to 3,000 rpm volts 0.850,0.375 0.135 then settles back to around 0.060 does this tell you anything ?
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Old 08-25-2009, 07:20 AM   #14
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I noticed this yesterday I can be driving along at 45 mph A/F's in the 14's (same TP same rpm no-load ) A/F's will drop into the 10's 11's 12's then settle in the 13's for a while maybe 14 then will start this cycle all over again its worse at 60 mph @ 6% tp under no load A/F's will drop into the 9's 10's then settle around 12. I'am going to hard wire in my 0/2 sensor maybe I have a bad oem connector, I just replaced this 0/2 sensor with a oem replacement 1000 miles ago I can't think its bad already. ( If this doesn't work I'll just go to autozone and pick up a Bosch univ. 0/2 sensor today)
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Old 08-26-2009, 07:12 PM   #15
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Default Update:

Found the cause, after replacing the 0/2 sensor, which I got under warranty from Autozone I sprayed own everything with brake cleaner on the intake side looking for vac. leaks and found none, so I thought lets see if this cleaner might effect my A/F ratio if there was a small leak. surpise suprise I had my daughter watch my A/F's while I sprayed down the injector side of the Dynamic Chamber and wow around the #3 runner A/F's dropped from 14's to 12's although idle did'nt change.........So I orderd a new gasket for the Dynamic Chamber. ( I had reused that one three times over the years) Thanks for all the input.
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