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P0172 Code Fix? Here’s the Exact Fix (Step-by-Step)

Symptoms:

• Rough idle
• Black exhaust smoke
• Decreased fuel efficiency
• Illuminated check engine light

Tools Needed:

• DiagtPro X400 Scanner
• Multimeter
• Smoke test kit
• Vacuum gauge

Step 1: Test Fuel Trims

• Hook up DiagtPro to check fuel trim values. A reading of +20% or more indicates a rich condition.
• Use the multimeter to check O2 sensor voltage. A voltage above 0.45V suggests a rich mixture.

Step 2: Inspect Vacuum Leaks

• Listen for hissing near the intake manifold, throttle body, and vacuum hoses.
• Perform a smoke test to visualize vacuum leaks.

Step 3: Avoid This Mistake

• Don’t assume the O2 sensor is bad—test wiring first. Check for corrosion, damage, or wear on the wiring harness.
• Warning: Ignoring wiring harness corrosion can lead to further damage and incorrect diagnoses.

Final Fix:
Replace the Mass Airflow (MAF) sensor, then clear codes with DiagtPro. Ensure to reset the fuel trim values and monitor the vehicle’s performance after the repair.