Bank 1 sensor 2 question
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Joined: Mar 2010
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From: Bushnell ,Fl
Just got back from town the codes that are coming up are P0171 and P0138. Thanks for your help! Ron
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Joined: Jul 2006
Posts: 12,204
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From: Gainesville, Ga.
ok, you have 2 different codes, maybe/maybe not related. both associated with O2 sensor feedback. this is what pisses me off about parts stores. any O2 related code is viewed as an opportunity to sell overpriced O2 sensors, regardless of the real problem.
P0138 is a FAILED rear O2, where the feedback signal is above its expected range, which means its most likely internally shorted to a 12v or 5volt signal. it needs to be replaced.
P0171 is a semi-normal lean condition. the front O2 appears to working correctly, but the PCM is pissed off that it's unable to adjust the fuel mix to achieve a proper emissions level in the exhaust pipe. this most likely indicates you plenum is leaking, which is a common problem with our trucks.
this is what i would do.
1. inspect the wiring on the rear O2 sensor wiring pigtail. look for any type of damage. if wiring damage is found, repair the wiring only and see if you can salvage the expensive little O2 sensor itself. wiring is simple, two 12v heaters (white), ground (?) and signal (?).
2. if no damage found, follow the pigtail up around the top of the trans and find the connector. unplug it and determine if the plug is round or square. make a note of that.
3. reset pcm and monitor it for a few days. recheck codes frequently, or as soon as CEL comes back on. see if one code appears before the other.
4. if P0138 comes back, and you want the CEL to go away, then replace rear O2. shop on internet. buy the correct shape plug (round vs square) or save money and buy a universal and splice it into your existing wiring pigtail, not into the main harness. (no harm in this). get a less expensive NGK or Denso or something and avoid the expensive $60 bosch at autozone. you can get one on the internet for 30-40.
5. check your plenum. it the likely cause of P0171. you can replace front O2 if you wish, but it most likely will not cure that code. that code indicates a vac leak.
P0171
http://www.obd-codes.com/p0171
Technical Description
System Too Lean (Bank 1)
What does that mean?
Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.
Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.
Symptoms
You will more than likely not notice any drivability problems, although there may be symptoms such as a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration.
Causes
A code P0171 may mean that one or more of the following has happened:
The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak downstream of the MAF sensor.
Possible solutions include:
In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect all vacuum and PCV hoses, replace if necessary
Check for a dirty fuel filter and proper fuel pressure
P0138
http://www.obd-codes.com/p0138
Technical Description
O2 Oxygen Sensor Circuit High Voltage (Bank1, Sensor2)
What does that mean?
The Heated Oxygen Sensor (2) located rear of catalytic converter produces an output signal relative to oxygen storage capacity of catalytic converter. Ho2S 2 signal is less active than signal produced by front oxygen sensor. This code sets when HO2 Sensor voltage is greater than 999 mV for more than 2 minutes (time depends on model. Could be as high as 4 minutes)
Symptoms
There may be no noticeable symptoms except for MIL illumination. Possible high fuel pressure can over rich the system.
Causes
A code P0138 may mean that one or more of the following has happened:
Faulty O2 sensor
Short to battery voltage in O2 sensor signal circuit
High fuel pressure (not as likely)
Possible Solutions
Replace O2 sensor
Repair short to battery voltage in o2 sensor signal circuit
P0138 is a FAILED rear O2, where the feedback signal is above its expected range, which means its most likely internally shorted to a 12v or 5volt signal. it needs to be replaced.
P0171 is a semi-normal lean condition. the front O2 appears to working correctly, but the PCM is pissed off that it's unable to adjust the fuel mix to achieve a proper emissions level in the exhaust pipe. this most likely indicates you plenum is leaking, which is a common problem with our trucks.
this is what i would do.
1. inspect the wiring on the rear O2 sensor wiring pigtail. look for any type of damage. if wiring damage is found, repair the wiring only and see if you can salvage the expensive little O2 sensor itself. wiring is simple, two 12v heaters (white), ground (?) and signal (?).
2. if no damage found, follow the pigtail up around the top of the trans and find the connector. unplug it and determine if the plug is round or square. make a note of that.
3. reset pcm and monitor it for a few days. recheck codes frequently, or as soon as CEL comes back on. see if one code appears before the other.
4. if P0138 comes back, and you want the CEL to go away, then replace rear O2. shop on internet. buy the correct shape plug (round vs square) or save money and buy a universal and splice it into your existing wiring pigtail, not into the main harness. (no harm in this). get a less expensive NGK or Denso or something and avoid the expensive $60 bosch at autozone. you can get one on the internet for 30-40.
5. check your plenum. it the likely cause of P0171. you can replace front O2 if you wish, but it most likely will not cure that code. that code indicates a vac leak.
P0171
http://www.obd-codes.com/p0171
Technical Description
System Too Lean (Bank 1)
What does that mean?
Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.
Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.
Symptoms
You will more than likely not notice any drivability problems, although there may be symptoms such as a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration.
Causes
A code P0171 may mean that one or more of the following has happened:
The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak downstream of the MAF sensor.
Possible solutions include:
In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect all vacuum and PCV hoses, replace if necessary
Check for a dirty fuel filter and proper fuel pressure
P0138
http://www.obd-codes.com/p0138
Technical Description
O2 Oxygen Sensor Circuit High Voltage (Bank1, Sensor2)
What does that mean?
The Heated Oxygen Sensor (2) located rear of catalytic converter produces an output signal relative to oxygen storage capacity of catalytic converter. Ho2S 2 signal is less active than signal produced by front oxygen sensor. This code sets when HO2 Sensor voltage is greater than 999 mV for more than 2 minutes (time depends on model. Could be as high as 4 minutes)
Symptoms
There may be no noticeable symptoms except for MIL illumination. Possible high fuel pressure can over rich the system.
Causes
A code P0138 may mean that one or more of the following has happened:
Faulty O2 sensor
Short to battery voltage in O2 sensor signal circuit
High fuel pressure (not as likely)
Possible Solutions
Replace O2 sensor
Repair short to battery voltage in o2 sensor signal circuit
Last edited by dhvaughan; Mar 4, 2012 at 12:29 PM.
Thread Starter
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Rookie
Joined: Mar 2010
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From: Bushnell ,Fl
Thank you so much for your help!! Today I got under the truck and lo'anbehold while tracing down the wire I found were some nukle head spliced a wire half a$$ ,,,,,I fixed it reset pcm and ta da no light 50 miles +.. Maybe my millage will improve!!
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Please help p0138 code
I keep getting a p0138 code I replaced the sensor new fuel pump checked all the wires traced it all the way to the main pigtail using a wire diagram and the code keeps coming back but it only comes back on when my wife (the truck) starts to sputter and loses power. I was told by a Ford and Chevy mech and they both said that it could possibly be a clogged cat that is causing all the issues. Please help
