P1128 OBD Code Definition:
P1128 Manifold Absolute Pressure Sensor Signal Lower Than Expected
P1128 OBD Code Description:

Possible causes
– Engine mechanical condition
– Faulty Manifold Absolute Pressure (MAP) sensor
– Manifold Absolute Pressure (MAP) sensor harness is open or shorted
– Manifold Absolute Pressure (MAP) sensor circuit poor electrical connection
Possible Symptoms
– Engine Light ON (or Service Engine Soon Warning Light)
P1128 OBD Code Description

The Manifold Absolute Pressure (MAP) sensor senses manifold absolute pressure (vacuum) and converts it into electrical signals. The MAP sensor outputs low signal voltage at high-vacuum (idling) and high signal voltage at low-vacuum (throttle valve wide open).

The engine control module (ECM) compares a predetermined MAP value at a given throttle position and manifold absolute pressure to the output voltage value of the MAP sensor.

If the MAP sensor outputs lower voltage than expected, the ECM detects a malfunction and stores a DTC.

Possible Solutions

  • Check Mass Air Flow (MAF) Sensor
  • Check Oxygen Sensor Control
    • Check Oxygen Sensor(s)
  • Check Fuel Injector(s)

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