2000 Chevy Blazer LS 4-Door with Hatch: Fixing P0171 and P0174 OBD2 Codes for Smog Pass
My 2000 Chevrolet Blazer LS 4-door with hatch failed smog inspection due to OBD2 diagnostic codes P0171 and P0174. These codes indicate a lean air-fuel mixture in the engine, which can cause poor emissions performance and trigger the service engine light (which comes on and off intermittently). I've already replaced the gas cap, completed an oil change, and previously had a high school friend—whom I believed to be a master mechanic—remove tubing from the main air intake system. However, he never returned to reassemble or replace the lines. I’ve paid for my DMV tags and insurance, but I’m now looking for affordable solutions to get this vehicle passed smog without further expense. A local auto shop quoted $115 for diagnosis—seems high, especially considering modern diagnostics are typically less costly. The truck’s 4x4 and heater systems don’t work, but those aren't urgent concerns. I previously had a tune-up last year, but I’ve learned that 'tune-ups' on modern engines like this one are not effective or necessary. My question is: what are the most likely causes of P0171/P0174? What repairs would be needed and how much might they cost? Can I purchase replacement parts (like vacuum hoses) and install them myself to save money, then have a professional verify the fix? Any suggestions or guidance on diagnosing and fixing this issue—especially with a budget-conscious approach—would be greatly appreciated.
The P0171 and P0174 codes point to a lean air-fuel mixture. The $115 diagnosis fee is on the higher side for basic OBD2 diagnostics—consider it a red flag, not a standard rate. A vacuum leak is one of the most common causes of these lean conditions, especially when paired with issues like 4x4 and HVAC system failures (both of which rely on engine vacuum). If your friend removed intake tubing, that could be a source of a vacuum leak—especially if the lines were disconnected without proper reinstallation. Note: The term 'tune-up' is outdated for modern engines. Modern vehicles don’t require traditional tune-ups; they rely on electronic fuel injection and sensors. If your friend removed components, those parts must be reinstalled or replaced to restore system integrity. Otherwise, the vehicle will continue to show lean codes. A basic check of fuel pressure should also be performed—low fuel pressure can contribute to a lean condition in fuel-injected engines. For more details: https://www.obd-codes.com/p0171 \ https://www.obd-codes.com/p0174