Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P1128: Manifold Absolute Pressure Sensor Signal Lower Than Expected
2004 Acura 3.5RLSECTION DTC P1128: Manifold Absolute Pressure Sensor Signal Lower Than Expected
WARNING: This page is about a different car, the 2003 Acura MDX. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION:
When substituting or replacement of PCM is recommended, see PCM REMOVAL & REPLACEMENT
for important precautions.
- Turn ignition switch on. Using Honda PGM Tester or the HDS, check MAP sensor in the DATA list. If MAP reading is 54.1 kPa or 1.61 volt or more for more than 5 seconds, go to step 5 . If MAP sensor reading is not as specified, go to next step.
- Using Honda PGM Tester or the HDS, do the DTC CLEAR in the CLEAR menu. Start engine . Hold engine at 3000 RPM with no load in (Park or Neutral) until the radiator fan comes on, then let engine idle.
- Test drive vehicle under the following conditions:
- Engine coolant temperature more than 158°F (70°C).
- Engine speed between 1100 and 6000 RPM.
- A/T in "D" position.
- Vehicle speed is accelerated from 16 MPH to 31 MPH with half throttle.
- Using Honda PGM Tester or the HDS, monitor the OBD STATUS for DTC P1128 in the DTCs menu. If it is FAILED, go to next step. If it is PASSED problem is intermittent, system is OK at this time. If it is NOT COMPLETED, go to step 2 and recheck.
- Turn ignition off. Replace the MAP sensor. Turn ignition on. With the Honda PGM tester or the HDS, do PCM RESET in the CLEAR menu. Do the PCM idle learn procedure. See PCM IDLE LEARN PROCEDURE .
- Start engine . Hold engine at 3000 RPM with no load in (Park or Neutral) until the radiator fan comes on, then let engine idle. Test drive vehicle under the following conditions:
- Engine coolant temperature more than 158°F (70°C).
- Engine speed between 1100 and 6000 RPM.
- A/T in "D" position.
- Vehicle speed is accelerated from 16 MPH to 31 MPH with half throttle.
- Check for Temporary DTCs or DTCs in the DTC menu. If DTC P1128 is set, check for poor connections or loose terminals at MAP sensor and PCM harness connectors. Go to step 1 . If any other Temporary DTCs or DTCs are set, troubleshoot those indicated. If Temporary DTCs or DTCs are not set, go to next step.
- Monitor the OBD STATUS for DTC P1128 in the DTCs menu with the Honda PGM tester or the HDS. If it PASSED, troubleshooting is done. If it is FAILED, check for poor connections or loose terminals at MAP sensor and PCM harness connectors. Go to step 1 . If it is NOT COMPLETED, go to step 6 .
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.