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BigBlock434
BigBlock434, Chevy Mechanic
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Experience:  ASE Master certified and 100% General Motors trained in all fields
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My 2002 chevy suburban 5.3L keeps throwing P0137 codes, even

Customer Question

My 2002 chevy suburban 5.3L keeps throwing P0137 codes, even after I have replaced both cats and rear O2 sensor that it is saying there is a low voltage condition. second O2 sensor same code. both pre cat O2 sensors have same voltage reading,. bank one voltage os rear O2 sensor keeps showing little to no voltage (checked with Snap-On scan tool by mechanic) what are possible solutions?
Submitted: 5 years ago.
Category: Chevy
Expert:  BigBlock434 replied 5 years ago.
There are many things that can cause a lean condition. Bad wiring to the affected HO2 sensor, corroded ground to the PCM(power control module),Clogged injectors, fuel contamination, low fuel preesure, Exhaust leaks, Vacum leaks. Do you have access to a onboard scanner to monitor the HO2 sensors? If you do find out which sensor is being affected. Does the engine run rough at idle? If it does take a butane bottle and check for vacum leaks at the intake at idle, if you don't have a butane bottle then use a can of brake clean. Be very careful with this one and spray little amounts at a time(always have a extinguisher handy at all times).
Customer: replied 5 years ago.
the affected sensor is bank one rear. the mechanic monitored the condition as it was runniing and the pre cat o2 sensors showed the same voltage, however the after cat sensors were different with bank one showing little to no voltage. the engine does not run rough at idle, however the idle rpms are around 500-600, would this be considered rough?
Expert:  BigBlock434 replied 5 years ago.
No that is about normal on the idle. Let me make sure we are on the same page. Vehicle has four sensors two before the cats and two behind the cats. The ones in front monitor the engine performance, the ones behind the cats monitor the effectiveness of the cats ability to convert exhaust into unharmful emissions. Which sensor is reading wrong?
Customer: replied 5 years ago.
the sensor reading wrong is behind the cat (last sensor before muffler) monitoring the cat. on the drivers side. the sensors in front of the cat say the engine is running normally based on what you're saying.
Expert:  BigBlock434 replied 5 years ago.
<p>Okay if you are having a different reading on bank 1 sensor two(Drivers side after the converter) then check:</p><p>#1 wiring to the affected sensor.</p><p>#2 Are these aftermarket catalytic converters? If so the muffler shop drills a hole in the pipe to check back pressure. Make sure you don't have any leaks in the affected pipe on that bank(I have seen aftermarket converters not perform to specs on GM vehicles)</p><p>#3 Are these after market sensors? If so switch catalytic monitoring sensors to make sure you don't have a bad one. </p><p>If you are having only the catalytic monitoring sensor tripping the code then it can't be the engine doing it.</p><p> </p>
Customer: replied 5 years ago.
yes, after aftermarket cats, yes after market sensors. will first check wiring, then switch sensors (bank one to bank two and vice versa) to eliminate bad sensor from equation, if wiring ok, and sensor still reads bad on bank one (after switching sides), then the probable cause is after market cat, would you agree? solution - go with factory cat?
Expert:  BigBlock434 replied 5 years ago.
Yes I will agree.

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