P0171, P0174m o2 sensors, etc.
07-09-2016, 04:36 PM
#1
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Thread Starter
P0171, P0174m o2 sensors, etc.
First, I want to thank everyone on the Corvette Forum for making this a wonderful resource! I've saved so much time, money and frustration researching here and learning from you folks.
I was getting P0171 and P0174 lean codes on my 2000 C5 Coupe with 143,800 miles on the odometer. I found a crack/hole in the PCV hose and installed a new hose. It wouldn't idle, so I went through the Idle Learning procedure, including driving it about 25 miles. It idles great now, in fact much better than it has for several weeks. The slight "hesitation" I was having on acceleration is also gone. If this hadn't fixed the code problem, I was going to replace the upstream o2 sensors.
Here's my question. While researching this issue, I saw a few posts indicating that changing the o2 sensors could not only cure a P0171/P0174 problem, doing so could also improve performance and fuel mileage. Since it appears that my code and check engine light sensor problem has been fixed, would there be any benefit in changing the o2 sensors anyway? Or can I assume that if they are not throwing codes they are working well?
Thanks,
Chas.
I was getting P0171 and P0174 lean codes on my 2000 C5 Coupe with 143,800 miles on the odometer. I found a crack/hole in the PCV hose and installed a new hose. It wouldn't idle, so I went through the Idle Learning procedure, including driving it about 25 miles. It idles great now, in fact much better than it has for several weeks. The slight "hesitation" I was having on acceleration is also gone. If this hadn't fixed the code problem, I was going to replace the upstream o2 sensors.
Here's my question. While researching this issue, I saw a few posts indicating that changing the o2 sensors could not only cure a P0171/P0174 problem, doing so could also improve performance and fuel mileage. Since it appears that my code and check engine light sensor problem has been fixed, would there be any benefit in changing the o2 sensors anyway? Or can I assume that if they are not throwing codes they are working well?
Thanks,
Chas.
07-09-2016, 08:22 PM
#2
Advanced
Thread Starter
If one were to look at the shop manual diagnostic charts for codes P0171 and P0174, none of the steps indicate that replacement of the O2 sensors is a corrective action. Nearly all the steps involve looking for air leaks in the systems that permit air into the combustion process.
The two codes you had are almost always the result of air leaks after the MAF. Either cracks in the tubes between the MAF and Throttle Body, loose clamps on those tubes, or as you found rotted tubes for the PCV system. The other major causes are exhaust leaks at the exhaust manifold and leaks around injector o'rings. In fact it is O2 sensors that are detecting those lean conditions.
Since you don't have other codes set I would suggest that the only thing you will benefit from by replacing O2 sensors is lightening your wallet.
There are a whole series of codes in the P0130 to P0161 range that could be set if you were experiencing O2 sensor problems.
The two codes you had are almost always the result of air leaks after the MAF. Either cracks in the tubes between the MAF and Throttle Body, loose clamps on those tubes, or as you found rotted tubes for the PCV system. The other major causes are exhaust leaks at the exhaust manifold and leaks around injector o'rings. In fact it is O2 sensors that are detecting those lean conditions.
Since you don't have other codes set I would suggest that the only thing you will benefit from by replacing O2 sensors is lightening your wallet.
There are a whole series of codes in the P0130 to P0161 range that could be set if you were experiencing O2 sensor problems.
Chas.