What component causes a p0171 system too lean bank one error code?
#1
Driver School Candidate
Thread Starter
What component causes a p0171 system too lean bank one error code?
help? my 98 ES has this emissions code (P0171) meaning she is running too lean & can't pass smog. The smog place that failed my ES did a diagnostic & smoked the engine for vacuum leaks. In result they replaced the valve cover gasket. Saying this was the cause and would pass if fixed. Still no pass even after i paid for all the repairs & tests. NOT COOL in my opinion. So i put in some new things, a new air filter, new gas filter, new PVC valve. New gas cap. New plugs, oil & filter with master tune up. Fuel pump tested & good. MAF swapped but still same issue. 2 mechanics say it's the PCU but i have doubts...I tried changing the PCU from a 98 Camry but when starting the car only for it to crank but no start. So i put the original back on. I have heard that a key reprogram has to be done in order to sync the computer to my ES. Any thoughts, comments, opinions? Thanks guys.
Last edited by ovoxolexus; 03-07-13 at 09:54 AM. Reason: new info
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turtlepeas (04-25-20)
#2
According to the Haynes manual, P0171 system too lean, and the causes could be any of the following:
loose air intake hose or duct
incorrect fuel line pressure
obstruction in injector
heated oxygen sensor malfunction
MAP or MAF sensor malfunction
ECT sensor malfunction
loose air intake hose or duct
incorrect fuel line pressure
obstruction in injector
heated oxygen sensor malfunction
MAP or MAF sensor malfunction
ECT sensor malfunction
#5
In my limited experience an P0171 is an O2 sensor failure. I have two 99 ES300's. Both showed P0171. In both, replacing the O2 sensor fixed the problem. Most people say the P0171 is a MAF problem. Not for me. It was the Bank 1 sensor 1 [Air and Fuel Ratio Sensor (O2 sensor)]. O2 sensor failure is a common problem.
Additionally it was the same for my 95 Camry V6 1mz-fe engine. That's the same engine the ES300s use.
Additionally it was the same for my 95 Camry V6 1mz-fe engine. That's the same engine the ES300s use.
Last edited by tomf; 03-08-13 at 02:15 PM. Reason: added more info
#6
In my limited experience an P0171 is an O2 sensor failure. I have two 99 ES300's. Both showed P0171. In both, replacing the O2 sensor fixed the problem. Most people say the P0171 is a MAF problem. Not for me. It was the Bank 1 sensor 1 [Air and Fuel Ratio Sensor (O2 sensor)]. O2 sensor failure is a common problem.
Additionally it was the same for my 95 Camry V6 1mz-fe engine. That's the same engine the ES300s use.
Additionally it was the same for my 95 Camry V6 1mz-fe engine. That's the same engine the ES300s use.
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Lesterkiwi (03-11-20)
#7
I guess since he swapped the MAF I just assumed it wasn't the MAF. Unless he replaced the original dirty one with a dirty one.
A A/F sensor is an O2 sensor with higher sensitivity. From the Denso website "Oxygen sensors have a smaller range of limits in detecting and adjusting the difference from an optimum air/fuel ratio."
See this explanation from Denso http://www.densoaftermarket.com/oxygen-sensor.php
See this explanation from Denso http://www.densoaftermarket.com/oxygen-sensor.php
Last edited by tomf; 03-09-13 at 10:38 AM. Reason: Added link.
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#8
I guess since he swapped the MAF I just assumed it wasn't the MAF. Unless he replaced the original dirty one with a dirty one.
A A/F sensor is an O2 sensor with higher sensitivity. From the Denso website "Oxygen sensors have a smaller range of limits in detecting and adjusting the difference from an optimum air/fuel ratio."
See this explanation from Denso http://www.densoaftermarket.com/oxygen-sensor.php
A A/F sensor is an O2 sensor with higher sensitivity. From the Denso website "Oxygen sensors have a smaller range of limits in detecting and adjusting the difference from an optimum air/fuel ratio."
See this explanation from Denso http://www.densoaftermarket.com/oxygen-sensor.php
#9
Driver School Candidate
Thread Starter
Thanks guys!!! I was running out of things to replace/swap emissions related. I will definitely have another look at the MAF sensor & also changing out the bank 1 O2 sensor.
#10
help? my 98 ES has this emissions code (P0171) meaning she is running too lean & can't pass smog. The smog place that failed my ES did a diagnostic & smoked the engine for vacuum leaks. In result they replaced the valve cover gasket. Saying this was the cause and would pass if fixed. Still no pass even after i paid for all the repairs & tests. NOT COOL in my opinion. So i put in some new things, a new air filter, new gas filter, new PVC valve. New gas cap. New plugs, oil & filter with master tune up. Fuel pump tested & good. MAF swapped but still same issue. 2 mechanics say it's the PCU but i have doubts...I tried changing the PCU from a 98 Camry but when starting the car only for it to crank but no start. So i put the original back on. I have heard that a key reprogram has to be done in order to sync the computer to my ES. Any thoughts, comments, opinions? Thanks guys.
If I were to delve into this unfortunate episode of swaptronics with you I'd shoot for O2 (A/F) sensor first and then look at all of my bank one fuel injectors after that.
If you feel like actually checking to see if either of these are actually the problem you could always try SWAPPING them from one side to the other to see if the code swaps out for the other. Make sure to clear the code in between or you could potentially see both codes at the same time.
If you plan on doing this first make sure the fuel injectors and O2 sensors are interchangeable from either side (they should be, but I have no way of being certain as I have a 2ES) and start with the injectors to save yourself from buying the O2 gaskets if the injectors are the problem.
(sorry for the long post)
#12
Sorry, but this is totally untrue. From my personal experience and many, many others who have posted on various Toyota/Lexus car forums, it is the norm to get just a single bank P0171 lean code caused by a dirty MAF sensor.
#14
If the battery is disconnected, or the codes are erased all of the monitors are cleared which makes for even less chance to pass the smog test until they all reset. A couple of drive cycles needs to be performed so the PCM can test the different systems and set the monitors again. If one monitor won't set, the remaining monitors will not even run as they go in order as per the executive director in the PCM. Clear as mud right.
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samsonn25 (01-25-20)
#15
O2 sensor failure is a known problem
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samsonn25 (08-09-19)