2oo0 chevy blazer cel and code p0171 and p0174

oxygen sensors can't be cleaned. They're porous. If they're silled with soot, you have to replace them. Plus, O2 sensors don't caused lean codes, they only report them. Stop looking at the oxygen sensors and look for a vacuum leak, low fuel pressure or clogged fuel injectors.

System Too Lean P0171
Clean the MAF sensor and IAC valve with MAF cleaner
Inspect all vacuum and PCV hoses, replace/repair as required.
Inspect all hoses and connections in the air intake system.
Inspect and/or test the intake manifold gaskets for leakage.
Check for a dirty fuel filter and proper fuel pressure.

As a last resort, replace O2 sensor

System Too Lean P0174
Error code P0174 is described as System Too Lean (Bank 2). This means there is incorrect ratio of air and fuel on the car's engine system, specifically on Bank 2 of the Cylinder. “Too Lean” means there is too much oxygen in the exhaust.

As a last resort, replace O2 sensor

P0171 and P0174 are lean codes. There is likely a large vacuum leak or the MAF is bad.

Try starting the car and wiggling the connector for the MAF sensor. Also try tapping the MAF sensor. If the idle changes or the car stalls replace the MAF sensor.

The second shop should recognize that these codes don't have anything to do with the ignition module.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

Could be a problem with the MAF sensor but if it is you should have a code for that too.
Other causes include low fuel pressure, and a vac leak or air leak in the intake hose to the MAF.
The codes mean the ECM can not make the injectors rich enough to make the O2 sensors switch back and forth.

P0171 system too lean bank 1
P0174 system too lean bank 2
links to information on the codes

it means that the O2 sensors in your vehicle detected a lean condition in their respective banks. this could be caused by a dirty MAF (mass air flow) sensor or a vacuum leak downstream from the MAF sensor

sometimes you can clean the MAF with electronics cleaner or brake cleaner but be sure to take it off the vehicle first. be careful not to damage the MAF while spraying the cleaner, and allow it to dry completely before installing it on the vehicle.

Clean the MAF Sensor---CRC MAF Cleaner
The maf sensor is fairly reliable and fairly expensive.
They just repair them,so I would say no

Vacuum leaks are the most likely,causing both banks, to drive the O2 Lean

Egr Valve worth checking out

Loose O2 Sensors

Exhaust letting air in

Ducting to throttle or air filter cover loose

Etc

I know this is an old post, but I found the solution for my 01' Yukon P0171 and P0174. I have changed all the vacuum line and the PCV, throtle body gasket, MAF, plugs wires, fuel pressure reg. All was changed and the codes always came back.

I finally noticed the purge valve on the manifold was constantly purging. I replaced the purge valve abnd code has not been back. It was $40.

LEAN TROUBLE CODES (P0171 or P0174) A code P0171 or P0174 indicate the engine is running lean. This means there is too much air and/or not enough fuel. You can confirm the engine is running lean by looking at Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). Normally, STFT and LTFT should be plus or minus 8 from zero. If STFT and/or LTFT are more than about +10 or higher, it indicates the engine is running LEAN. Negative numbers (-10 or more) indicates the engine is running RICH. A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)

______________________________-- 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 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

this sounds like you have a vacuum leak. what this is telling you is you dont have the right air/fuel mixture ratio and the o2 sensor is picking up the air rich burn. does the engine run rough? it could be a stuck injector. usaully vacuum though. happy holidays

P0171 - System Too Lean (Bank 1)
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.

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

P0174 is identical to P0171, except it indicates the problem exists on Bank 2 as well.