P1128 - FAULT CODE P1128 - OBD2

POST UPDATED IN February, 2023

P1128 Code failures by brands

P1128, JEEP, DODGE,  MITSUBISHI, CHRYSLER: CLOSED-LOOP FUELING NOT ACHIEVED BANK 1

Description of DTC code P1128

Fuel management systems are used to maintain and regulate engine fuel consumption. The design of these systems allows the measurement and the effective control of the fuel and consequently of the engine.

When the system works in a closed circuit, it is the Oxygen Sensor that is used for feedback control. The PCM (Powertrain Control Module) uses the input from these sensors to carry out the regulation of the fuel mixture, it is also known as the fuel feedback control circuit. The PCM relies on these signals and in response changes the fuel mixture. This process is known as a closed-loop since the PCM uses the sensor input to regulate the mixture, resulting in a round trip from rich to poor, achieving greater efficiency of the catalytic converter.

An open circuit is a condition in which no signal is received from the O2 Sensor, such as when the engine is started when it is cold. In these cases, the PCM gives the command for a fixed rich (immutable) fuel mixture. In case the Powertrain Control Module detects a condition where the vehicle has been running in open circuit, from the start of engine for more than a calibrated time, when the conditions required closed-circuit operation, the fault code P1128 OBDII will be set.

Symptoms of fault code P1128

  • Check Engine lamp on.
  • Decreased fuel efficiency.
  • Remarkable loss of engine power.

Causes of OBD2 P1128

The reasons why the diagnostic code P1128 OBD2 is set are

  • The components of the fuel supply system may have deficiencies.
  • The Manifold Absolute Pressure (MAP) sensor wiring or connectors may be damaged.
  • An Oxygen Sensor may be defective.

Possible solutions of the DTC code P1128

To solve the DTC code P1128 OBDII consider the following:

  • Check the TSB (Technical Service Bulletins). The manufacturer may be aware of this fault and can offer assistance in these bulletins.
  • Due to the complexity of this system and the large number of components involved, it is necessary to use a scanner to get all the stored Diagnose the codes according to the order shown in the tool to avoid unnecessary repairs or changes.
  • Check the good condition of the electrical components of the MAP Sensor and the Oxygen Sensors, as well as these sensors. Correct any conditions causing the malfunction.

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