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Discussion Starter #1
My Green Beauty is a teenager now (14 years young) and started to misbehave :wink:. Last week windscreen washer pump (replaced), this week "Check engine" light. I did OBDII scan using my home equipment and I got this:
Code:
[..]
MIL light ON, 1 stored DTC
 Requesting Mode 0x03 (Emission DTCs)...
 P0170
[..]
I did the reading about P0170 and looks like it will be job for my garage to figure out what's exactly is wrong. Additional info:
1. I could bet I smell fuel after starting the car during last week. Something that has never happened before. It was like engine was getting too much fuel in good old days without any electronics on-board.
2. Few time observed power fluctuation when driving at low speed. It was like I was moving my feet on the accelerator gently back and forth. Except I wasn't.
3. MIL light cam on when driving at 100 kph, a few minutes after very heavy acceleration. I got on a main road, up hill, so it was "pedal to the metal" up hill acceleration.


I want to ask dear forum: what's the most common reason of P0170 OBD-II Trouble Code: Fuel Trim Malfunction (Bank 1)?


MAF sensor? O2 sensor(s)?
 

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Discussion Starter #6
Thanks all for the input! I have some more info, but I have no reference values:
Code:
[..]
Parameter                      Current         FreezeFrame
Fuel System Status             Open-Fault      Closed         
Calculated Load Value            0.0%           28.6%         
Engine Coolant Temperature      83C             89C           
Short term fuel trim Bank 1      0.0%            2.3%         
Long term fuel trim Bank 1      16.4%           11.7%         
Intake Manifold Pressure       101kPaA          72kPaA        
Engine RPM                         0RPM         2765RPM       
Vehicle Speed                    0km/h         110km/h        
Ignition timing advance Cyl #1 63.5 deg        -----          
Intake Air Temperature          52C            -----          
Air Flow Rate                    0.00gm/s      -----          
Absolute Throttle Position      18.8%           22.7%         
Commanded Secondary Air Status                 -----          
Location of Oxygen Sensors                     -----          
Bank 1 Sensor 2 Voltage/Trim   1.000V          -----          
Requesting Mode 7 (Current cycle emission DTCs)...
Currently monitored DTCs: P0170 [..]
Does it make sense to reset the error and watch if it comes back? I should have access to a better scanner soon.


I guess this is the problem? Long term fuel trim Bank 1 16.4% 11.7%
 

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You're after cat lambda is showing a lean condition +16% this is the LTFT but the Short trim ( stft ) is in the range 2.3%. I had the same problem and it was the 2nd lambda ( downstream lambda ).
Drive the car and only observe the live data for STFT ( short fuel trim ) if this is in the range + / - 7 is definitely the 2nd lambda. If the stft is greater then +/- 7% then you have another problem.
On hard acceleration, you should see a negative stft -7% on steady cruse you should have as close as 0%.
 

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Discussion Starter #9
I did idle/1500/2500 test on cold ant hot engine. New error is showing up: Currently monitored DTCs: P0170 P0171
P0171 System Too Lean Bank 1
Results:
Ignition on, engine not started:
Short term fuel trim Bank 1 0.0%
Long term fuel trim Bank 1 16.4%
Bank 1 Sensor 2 Voltage/Trim 0.445V

Engine cold, idle (3 samples):
Short term fuel trim Bank 1 0.0% (stays at 0.0%)
Long term fuel trim Bank 1 11.7% up to 16.4%
Bank 1 Sensor 2 Voltage/Trim 0.485V

Engine cold (60 to 63 deg C), 2500rpm (3 samples):
Short term fuel trim Bank 1 1.5% to 3.1%
Long term fuel trim Bank 1 16.4% (stays at 16.4%)
Bank 1 Sensor 2 Voltage/Trim 0.280 to 0.290V

Engine hot, idle (2 samples):
Short term fuel trim Bank 1 -0.8%
Long term fuel trim Bank 1 16.4%
Bank 1 Sensor 2 Voltage/Trim 0.585V to 0.590V

Engine hot, 1500 rpm (4 samples):
Short term fuel trim Bank 1 0.0% to -3.9%
Long term fuel trim Bank 1 16.4% (stays at 16.4%)
Bank 1 Sensor 2 Voltage/Trim 0.585V to 0.640V

Engine hot, 2500 rpm (1 sample):
Short term fuel trim Bank 1 1.6%
Long term fuel trim Bank 1 16.4%
Bank 1 Sensor 2 Voltage/Trim 0.660V

I didn't do a test ride, but if I understand the system it will be the second lambda sensor.

Full log: PasteAll.org
Thanks again!
 

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I did idle/1500/2500 test on cold ant hot engine. New error is showing up: Currently monitored DTCs: P0170 P0171
P0171 System Too Lean Bank 1
Results:
Ignition on, engine not started:
Short term fuel trim Bank 1 0.0%
Long term fuel trim Bank 1 16.4%
Bank 1 Sensor 2 Voltage/Trim 0.445V

Engine cold, idle (3 samples):
Short term fuel trim Bank 1 0.0% (stays at 0.0%)
Long term fuel trim Bank 1 11.7% up to 16.4%
Bank 1 Sensor 2 Voltage/Trim 0.485V

Engine cold (60 to 63 deg C), 2500rpm (3 samples):
Short term fuel trim Bank 1 1.5% to 3.1%
Long term fuel trim Bank 1 16.4% (stays at 16.4%)
Bank 1 Sensor 2 Voltage/Trim 0.280 to 0.290V

Engine hot, idle (2 samples):
Short term fuel trim Bank 1 -0.8%
Long term fuel trim Bank 1 16.4%
Bank 1 Sensor 2 Voltage/Trim 0.585V to 0.590V

Engine hot, 1500 rpm (4 samples):
Short term fuel trim Bank 1 0.0% to -3.9%
Long term fuel trim Bank 1 16.4% (stays at 16.4%)
Bank 1 Sensor 2 Voltage/Trim 0.585V to 0.640V

Engine hot, 2500 rpm (1 sample):
Short term fuel trim Bank 1 1.6%
Long term fuel trim Bank 1 16.4%
Bank 1 Sensor 2 Voltage/Trim 0.660V

I didn't do a test ride, but if I understand the system it will be the second lambda sensor.

Full log: PasteAll.org
Thanks again!
Stft is ok.
LTFT is not moving while in idle for that you need to drive the car...
Drive the car and then observe the STFT if the STFT is over +15% don't dive it as you risk to burn the valves.
 

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6007.us
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Seems to be some mythconceptions here and need to see MAF, MAP if available, and O2 bank 1 senor 1 (upstream). Sensor 2 should not stay near the middle once warmed up unless the cat is bad/failing.

STFT or SHRTFT (short term fuel trim) will move around when in closed loop (warmed up). LTFT or LONGFT (long term fuel trim) should be pretty stable. Can thing of LT as the gross setting and ST as the fine setting. Have to add together. Is a computer decision based on a lot of things but not the downstream O2 (lambda).

Readings do indicate an inline 4 cyl (bank 1 only). Lean condition would match the 16.4 LTFT command. Could be a vaccuum leak, low fuel pressure, dirty injectors.

Here is what my V6 looks like warmed up at idle. Note it has bank 1 and bank 2:
DTC_CNT 0
FUELSYS1 CL (closed loop)
FUELSYS2 CL
LOAD_PCT 16.5 %
ECT (coolant temp) 189 °F
SHRTFT1 3.9 %
LONGFT1 -3.1 %
SHRTFT2 2.3 %
LONGFT2 -4.7 %
MAP 5.5 psi
RPM 692 rpm
VSS 0 mph
SPARKADV -17.5 °
IAT 160 °F
MAF 0.01 lb/s
TP 2.0 %
AIR_STAT OFF
O2B1S1 0.745 V
O2B1S2 0.780 V
O2B2S1 0.610 V
O2B2S2 0.755 V
OBDSUP OBDII
 

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Discussion Starter #12
Thanks again!! A short test ride results (filtered):
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 -3.1%
Short term fuel trim Bank 1 -5.5%
Short term fuel trim Bank 1 1.6%
Short term fuel trim Bank 1 -3.9%
Short term fuel trim Bank 1 -7.8%
Short term fuel trim Bank 1 -12.5%
Short term fuel trim Bank 1 3.9%
Short term fuel trim Bank 1 7.0%
Short term fuel trim Bank 1 7.0%
Short term fuel trim Bank 1 7.0%
Short term fuel trim Bank 1 6.2%
Short term fuel trim Bank 1 5.5%
Short term fuel trim Bank 1 -3.9%
Short term fuel trim Bank 1 -7.8%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 -5.5%
Short term fuel trim Bank 1 -8.6%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 -2.3%
Short term fuel trim Bank 1 3.1%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 6.2%
Short term fuel trim Bank 1 -14.1%
Short term fuel trim Bank 1 -7.8%
Short term fuel trim Bank 1 6.2%
Short term fuel trim Bank 1 -9.4%
Short term fuel trim Bank 1 7.8%
Short term fuel trim Bank 1 4.7%
Short term fuel trim Bank 1 3.9%
Short term fuel trim Bank 1 3.9%
Short term fuel trim Bank 1 -10.9%
Short term fuel trim Bank 1 0.0%
Short term fuel trim Bank 1 7.8%


Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 11.7%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 10.2%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 13.3%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 5.5%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 5.5%
Long term fuel trim Bank 1 5.5%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 5.5%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 13.3%
Long term fuel trim Bank 1 14.8%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 16.4%
Long term fuel trim Bank 1 6.2%

Full log: PasteAll.org
Full session log (freediag/scantool under linux): PasteAll.org
Search for "Parameter" in browser and hit "Next" - it nicely jumps between readings.



P.S. That ELM clone is another excuse to buy DAS/Star... :wink:
 

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Readings do indicate an inline 4 cyl (bank 1 only). Lean condition would match the 16.4 LTFT command. Could be a vaccuum leak, low fuel pressure, dirty injectors.
If you have a problem with that STFT will tell you immediately.
I run all my cars (4 in line, v6 ) on LPG so I ALWAYS monitor the LTFT and I tune my car with STFT
So in my experience, if the STFT is lean or rich you will see that in LTFT values.
If the STFT is in limits then the o2 downstream ( this reads the LTFT ) has a problem.
While i had my slk 200 I had a similar problem LTFT was +20% but the stft was in limits, it took a while for the 2nd lambda to show an error on my das machine.
I could be wrong but is too similar to my problem.
I have huge amounts of screenshots with LTFT as I want my car to run as near to 0% both banks, just my OCD.
 

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On r171 LTFT is changing slowly while driving, same on w204 c280 in the past, after i update the ecu LTFT is changing very fast like STFT, i am not sure what they change in the software but is hard to tune the car on LPG ...


On another note, we struggle almost one month on a vw r32 modified with turbo to tune the car and failed, in the end, the lambda were put incorrect in one pipe and not 2 separate pipes for bank 1 and bank2
 

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@racing_green

If I had a gun to my head, I'd say it was the MAF sensor. How many miles do you have on the car? If it's higher mileage, I'd be inclined to double down on that bet. Last year I replaced the MAF sensor on my '99 C280 (~75K miles), and a Bosch sensor cost me $130. I don't know if such an expenditure is a good bet for you to make, or if you'd prefer to have a better diagnosis. You could try to get some electronics parts cleaner spray and try that on the MAF. But that didn't work on mine, and I'm a bit skeptical if it does any good at all.

Otherwise, I'd try to get a better code reader to see if there's anything else you can figure out.

Good luck.
 

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Discussion Starter #17
It's getting close to 200kkm, so you could be right. The car is in a garage - I should get info what's going on today.
 

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@racing_green

If I had a gun to my head, I'd say it was the MAF sensor. How many miles do you have on the car? If it's higher mileage, I'd be inclined to double down on that bet. Last year I replaced the MAF sensor on my '99 C280 (~75K miles), and a Bosch sensor cost me $130. I don't know if such an expenditure is a good bet for you to make, or if you'd prefer to have a better diagnosis. You could try to get some electronics parts cleaner spray and try that on the MAF. But that didn't work on mine, and I'm a bit skeptical if it does any good at all.

Otherwise, I'd try to get a better code reader to see if there's anything else you can figure out.

Good luck.
If the maf was bad the stft will be out of specks.
 

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Discussion Starter #19
The car was in the garage a bit longer than expected. They told me it's the front lambda sensor. 245 euro for labour + parts and some cat cleaner. The cat cleaner in the tank, the tank topped up to full, 27 km later at 120 kph the light was back.... :surprise:

Options:
1. The garage was wrong - it's not the front lambda sensor
2. The garage was right, but the cat and/or the other lambda is damaged as the result of driving about 60-70 km to get home after the light came on initially.
3. The garage was right and I just need to burn the cat cleaner, reset the error and it will be all good again.

Other options?
It has happened in very similar conditions - I guess SLK has the tank vapour burning system? (I'm just thinking...)
The garage is using some diagnostic system, but it's not DAS/Star.

P.S. I did another test ride, full log here [1]. Filtered log: [2]
[1] PasteAll.org
[2] PasteAll.org

The frozen frame:
Code:
Parameter                      Current         FreezeFrame
Fuel System Status             Closed-Fault    Closed
Calculated Load Value            7.5%           31.8%
Engine Coolant Temperature      88C             89C
Short term fuel trim Bank 1     -5.5%           -2.3%
Long term fuel trim Bank 1      15.6%           14.1%
Intake Manifold Pressure        31kPaA          76kPaA
Engine RPM                      1504RPM         2995RPM
Vehicle Speed                   20km/h         120km/h
Ignition timing advance Cyl #1 29.0 deg        -----
Intake Air Temperature          30C            -----
Air Flow Rate                    9.61gm/s      -----
Absolute Throttle Position      14.9%           24.7%
Commanded Secondary Air Status                 -----
Location of Oxygen Sensors                     -----
Bank 1 Sensor 2 Voltage/Trim   0.410V          -----
Requesting Mode 7 (Current cycle emission DTCs)...
Currently monitored DTCs: P0170
Code:
$ grep trim slk_after_front_lambda_change_filtered.log  | grep Short
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      4.7%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      7.8%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      5.5%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      8.6%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1     -3.9%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      3.9%          
Short term fuel trim Bank 1      4.7%          
Short term fuel trim Bank 1     -0.8%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1     10.9%          
Short term fuel trim Bank 1      2.3%          
Short term fuel trim Bank 1     -7.8%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1     -2.3%          
Short term fuel trim Bank 1      7.0%          
Short term fuel trim Bank 1     -1.6%          
Short term fuel trim Bank 1      1.6%          
Short term fuel trim Bank 1    -18.8%          
Short term fuel trim Bank 1    -16.4%          
Short term fuel trim Bank 1     -3.1%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      5.5%          
Short term fuel trim Bank 1      5.5%          
Short term fuel trim Bank 1      0.8%          
Short term fuel trim Bank 1     -3.9%          
Short term fuel trim Bank 1      0.0%          
Short term fuel trim Bank 1      8.6%          
Short term fuel trim Bank 1      2.3%          
Short term fuel trim Bank 1      5.5%          
Short term fuel trim Bank 1     -0.8%          
Short term fuel trim Bank 1     -5.5%          
fedora:/home/przemo
$ grep trim slk_after_front_lambda_change_filtered.log  | grep Long
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1       6.2%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      13.3%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1       7.0%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      10.2%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1       6.2%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1       6.2%          
Long term fuel trim Bank 1      15.6%          
Long term fuel trim Bank 1      15.6%
 

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The STFT is in normal range except 3 or for values ( i assume the positive +10.9% was during deceleration and -18.8% under very hard acceleration ).
If any of the sensors are bad, MAF, MAP, front lambda, air leak, bad injector, clogged air filter bad fuel, a bad pressure to injectors, bad compression the STFT will be the first to suffer and will fluctuate badly in idle or under acceleration, yours is steady.
In your case the STFT is ok is only the LTFT which is +15.6, I will look to see if you have any leak/hole after the first lambda and 2 lambdas.
Why the garage put catalytic cleaner? Did they found that the backpressure is high or?
I still believe is your 2nd lambda at fault if it was 1st lambda again your STFT will be out of specs.
Now, a 2nd lambda is £60-70 any garage will charge you 30m, I will try this first.

Also in das you can check each component to see if is in specs take a look at the maf
https://imgur.com/a/9vdha
 

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