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DTC codes / Honda codes / P1129

P1129 · HondaMAP Higher Than Expected

P1129 on Honda vehicles means the powertrain control module has detected a manifold absolute pressure (MAP) sensor signal that is higher than the value it expects for the current engine operating conditions. The computer compares the MAP reading against throttle position, engine speed, and airflow models, and flags this code when the sensor voltage or calculated pressure exceeds the plausible range.

SystemPowertrain
Code typeHonda specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Check Engine Light illuminated, often with no other noticeable symptoms
  • Rough idle or unstable engine speed at stops
  • Hesitation or stumble during acceleration
  • Poor fuel economy or rich-running smell from the exhaust
  • Black smoke or soot from the tailpipe in severe cases
  • Engine may enter limp mode with reduced power on some Honda models

Common causes, most likely first

  1. Faulty MAP sensor reading high due to internal failure or contamination
  2. Vacuum leak between the intake manifold and MAP sensor port, or a cracked sensor O-ring
  3. Clogged or restricted MAP sensor vacuum port or hose
  4. Wiring issue such as a short to voltage on the signal circuit or poor ground
  5. Dirty throttle body or intake carbon buildup causing airflow model mismatch
  6. Aftermarket air intake or incorrect sensor installed by a previous repair
  7. Rarely, a PCM calibration issue or failed PCM driver

How to diagnose and fix it

  1. Connect a scan tool and record freeze-frame data for P1129, then compare MAP voltage and pressure readings to Honda specifications at key-on and idle.
  2. Inspect the MAP sensor vacuum hose and intake port for cracks, blockage, or loose connection, and repair or replace as needed.
  3. Check the MAP sensor electrical connector for corrosion, backed-out pins, or a short to voltage on the signal wire using a multimeter.
  4. Clean the throttle body and intake passages if carbon buildup is present, then perform an idle relearn if required.
  5. Swap in a known-good MAP sensor and recheck live data to confirm the reading normalizes before condemning the original sensor.
  6. Verify that the intake system is stock and that the correct Honda MAP sensor part is installed, replacing any aftermarket intake or wrong sensor.
  7. If all inputs and wiring test good, check for PCM software updates or perform a pinpoint test for a faulty PCM driver before replacement.

What Honda techs check before replacing the MAP sensor

  • A MAP sensor that reads higher than expected often has a partially blocked vacuum port rather than a failed sensor, so always inspect the port and hose before buying parts.
  • Honda intake manifolds can develop small vacuum leaks at the MAP sensor grommet that are invisible without a smoke test, and these leaks mimic a bad sensor perfectly.
  • Aftermarket air intakes change airflow characteristics and frequently set P1129 on Hondas even when the MAP sensor itself is healthy, so verify the intake is stock.
  • A dirty throttle body on Honda engines can cause the PCM to see a MAP value outside its expected model, so cleaning the throttle body and performing an idle relearn often resolves the code.
  • P1129 does not always mean the MAP sensor is faulty; a short to voltage on the signal wire or a poor sensor ground can produce the same high-reading symptom.

Can I keep driving with P1129?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or sustained high-speed driving because a rich fuel mixture can damage the catalytic converter over time. If the engine runs rough or enters limp mode, stop driving and arrange a tow.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Honda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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