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P0172Cars & SUVs
Moderate

P0172 — System too rich (Bank 1)

The ECM detects too much fuel relative to air on Bank 1. That can raise fuel use, cause a raw fuel smell, and foul the catalyst early.

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Likely causes

  • Leaking or stuck-open injector
  • Faulty MAF or MAP sensor sending a bad signal
  • Fuel pressure too high (failed regulator)

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Recommended checks

  1. 1

    Flow-test and leak-test the injectors

  2. 2

    Check MAF/MAP values at idle and under load

  3. 3

    Measure fuel pressure at the regulator

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Parts to replace