I have an 05 Hyundai Tucson with 2.7L engine with 85,000 miles. It is setting a P0171 lean bank one code. However, both banks are operating at near the high threshold levels around 14.8%. Numerous attempts and test have been tried to resolve the issue. ECM has been reset to base several times and the fuel trims follow the exact same pattern each time while driving the same highway pattern. It typically only takes around 15 miles for LTFT to rise from 0 to 14.8% on B1 with B2 closely behind. When B1 does set the P0171 code it's not storing any freeze frame data to help locate a possible cause. Anyone have any ideas why no FFD's? Any help would be greatly appreciated. Thanks, Ronnie3945
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Welcome to Motor Vehicle Maintenance & Repair!– Pᴀᴜʟsᴛᴇʀ2 ♦Commented Jul 1, 2018 at 13:13
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What testing was done? Can you create a datalog at idle, snap throttle and cruise?– BenCommented Jul 1, 2018 at 14:37
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It hasn't ever reached the threshold at idle to set a code. I have monitored FT's, O2S11 and O2S21. All appear to be normal.– Ronnie3945Commented Jul 2, 2018 at 15:09
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1Have you tried swapping the sensors between the banks and does the issue then change banks or not - may indicate a faulty sensor... have you checked the wires / connections thoroughly?– Solar MikeCommented Jul 4, 2018 at 6:03
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I agree with Solar Mike. My first instinct is an O2 sensor.– David SainCommented Sep 30, 2018 at 5:09
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1 Answer
I can only speculate why no freeze frame data is being stored with the p0171. My "guess" would be that it is a 2 trip code, and you are seeing a pending code on the first trip.
When it comes to p0171, you don't really need freeze frame to help you out. Since this code is a direct result of fuel trim, the next logical step is to see if the total fuel trim, (short term plus long term) rise at an idle, under a load, or remain constant at idle and load.
Watching the fuel trim behavior under different operating conditions will eliminate more possibilities for p0171 than Freeze frame data.
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Basically this is what's happening. After ECM reset all fuel trims at 0. Cold start STFT'S start to rise in response to O2 sensors. STFT's rise ~10% at idle. Begin road test normal driving. STFT'S rise to ~15-20% and LTFT's begin to rise. Within first six miles LTFT's have risen to ~8-10% and STFT'S drop in response. Continue driving onto four lane. Cruise at 70 mph. STFT's stay positive 3-6%. LTFT's continue to rise accordingly. After driving ~11 miles the LTFT's have reached around 14-15%. STFT's still slightly positive 1-5%. From this point normal driving the LTFT's remain ~14-15%. Commented Jul 2, 2018 at 12:07
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Test performed so far are as follows: fuel pressure at idle and higher rpm, steady at 47-48%. Smoke test for vacuum leaks. Checked purge & pcv systems, no leaks. Replaced MAF with non OEM part, no major changes. Ran multiple cans fuel cleaner thru tank. Took to dealer shop mechanic still leaning towards MAF. Mechanic said needs freeze frame data to help locate cause. There are no drivability issues. Both banks are operating nearly identical in all systems. Bank one is only operating slightly higher than bank 2. So, obviously what ever the cause it's common to both banks. Commented Jul 2, 2018 at 12:24
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I have agreed with dealer shop to purchase an OEM MAF from them to prove or disprove the issue. However, there are stipulations. Since their tech believes the MAF is at fault if replacing it with the OEM does not correct the problem they will take it back no cost to me. Commented Jul 2, 2018 at 12:31