What does it mean?
P1129 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Manifold Absolute Pressure (MAP) Sensor Signal Higher Than Expected .
Symptoms
- Malfunction indicator lamp on together with a rough, unstable idle
- Rich running, black smoke and a strong exhaust smell
- Poor fuel economy and sooty spark plugs
- Hesitation or bogging when the throttle is opened quickly
- A hissing or whistling noise from the engine bay at idle
Likely causes
- Unmetered air entering through a cracked intake boot, split vacuum line or leaking intake manifold gasket
- Leaking or loose MAP sensor seal, o-ring or mounting grommet
- Throttle plate held slightly open by carbon build-up or a sticking linkage
- Loss of engine vacuum from worn valve seats, a stretched timing chain or incorrect cam timing
- Sensor element drifted high, or a signal wire shorted to the 5 V reference
- Leaking brake booster, PCV valve or purge valve bleeding air into the manifold
- Low compression across several cylinders reducing manifold vacuum
How to fix it
- Record MAP live data at idle and compare it against a vacuum gauge; a healthy warm engine pulls steady, high vacuum
- Check barometric versus MAP reading at key on, engine off to see whether the sensor is biased high
- Smoke test the intake tract and vacuum lines to find unmetered air leaks
- Inspect the MAP sensor seal, mounting and hose, and check the throttle plate rest position
- Measure signal voltage at the PCM connector with the sensor unplugged to rule out a short to reference
- Perform a cylinder leakage or compression check if vacuum is low, unsteady and no leak is found
- Replace the MAP sensor last, then clear codes, reset fuel trims and road test