Yep, probably time for an O2 sensor change if it's an erratic, intermittent code due to the age of your vehicle. Hell, I am way overdue for mine to be replaced... Thankfully no such problem yet with my truck. Check your hoses and sensors for the air intake system as well.(MAP sensor too!)

You're getting a "System too lean (Bank 1)" code:

https://www.obd-codes.com/p0171

What does that mean?

This diagnostic trouble code (DTC) is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may be slightly different depending on the model. So this engine code article applies to Toyota, Chevrolet, Ford, Nissan, Honda, GMC, Dodge, etc. Basically this means that an oxygen sensor in bank 1 has 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. The P0171 is one of the more common trouble codes. This code is triggered by the first downstream (front) O2 sensor. The sensor provides a reading of the air:fuel ratio leaving the engine's cylinders, and the vehicles powertrain/engine control module (PCM/ECM) uses that reading and adjusts to keep the engine running at that optimum ratio of 14.7:1. If something is not right and the PCM cannot maintain the 14.7:1 ratio, but rather there is too much air, it triggers this code. You'll want to also read our article on short and long term fuel trims to help understand the operation of the engine. 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) rough idle 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 cracked vacuum or PCV line/connection Faulty or stuck open PCV valve Failed or faulty oxygen sensor (bank 1, sensor 1) Sticking/plugged or failed fuel injector Low fuel pressure (possible plugged/dirty fuel filter!) Exhaust leak between engine and first oxygen sensor Possible

Solutions

A lot of times, cleaning the MAF sensor and finding/fixing vacuum leaks fix the problem. If you're on a tight budget, start there, but that may not be the fix for certain. So, possible solutions include: Clean the MAF sensor. 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 CRC MAF Sensor 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/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. Ideally you'll want to monitor short and long term fuel trims using an advanced scan tool If you have access, you may want to run a smoke test.

Read more at: https://www.obd-codes.com/p0171
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https://www.obd-codes.com/p0171

 

Yea, I'll probably/should clean the MAP while I'm at it. Plan is that while I'm taking everything off to clean TB, go ahead and clean as much of the intake system as I can.

 

Some trucks have had intake manifold gasket leak issues which could cause this. You should be able to test this by spraying "starting Fluid" around the intake mounting flange with the engine idling. RPM increase =leak found!

 

I have an 04 Colorado with the 5 cyl engine. Do the same problems apply to this engine? Could a dirty air filter be the culprit? Just had the oil changed and was told the air filter needed changed. Did not want to pay $25.00 for a filter at the dealer when I can get it cheaper at a parts store.

 

The Atlas series engines (I-4, I-5 and the Trailblazer's I-6) all share about roughly 90% of their parts, so yes, they are all roughly identical and the codes all apply for the same problems across all the engines.

What problem(s) are you having? Do you have this code on your truck? Until you can answer these questions, I wouldn't replace anything, unless your air filter hasn't been replaced in over a year or so I'd say. I certainly wouldn't pay a dealership for anything either unless I just wanted to get my wallet raped, or had no other option or source for that part.

 

Check the mounting bolts on the engine side of the intake manifold. I (and a few others) had this issue a while back and found that 3 of the bolts had backed out. Tightened them up and problem never came back. They're kind of a pain to get to but accessible through the wheel well after removing the splash guard. You'll need a universal, long extention, and i believe it's a 10 mm socket. The bolts have keepers on them so they can't fall out. Def worth checking before throwing money into parts.