Error “System too lean bank 1 and 2” meaning

The error “system too lean bank 1 and 2” is an issue with the air/fuel ratio in your engine being too lean. If you’re using an OBD scanner, this shows up as code P0171 for bank 1, and code P0174 for bank 2. There are several possible causes:

  • There is a leak between the MAF or MAP sensor and the rest of the intake, giving the ECU a false air reading. This is usually caused by a loose clamp or a disconnected hose to the intake.
  • The injectors aren’t spraying enough fuel. This could be caused by clogged injectors or low fuel pressure caused by a bad fuel pump or clogged fuel filter.
  • The O2 sensors are bad, giving the ECU a false reading.

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