Code Definition

P1128 — Manifold Absolute Pressure (MAP) lower than expected

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Honda

About P1128

P1128 is a manufacturer-specific powertrain diagnostic trouble code recorded for Honda vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1128 is stored, the module has detected a signal or supply voltage lower than the expected operating range.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1128 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The Manifold Absolute Pressure (MAP) sensor measures intake manifold pressure and reports it to the Powertrain Control Module (PCM) as a load signal for fuel and ignition control. DTC P1128 is a Honda specific code that sets when the PCM detects the MAP sensor reading is lower than the value expected for the current throttle position, engine speed, and load. A lower than expected MAP signal means the sensor is reporting more vacuum, or less absolute pressure, than the operating conditions should produce, which usually points to a sensor or vacuum supply fault rather than a true engine conditio...

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