Fuel and air

P0129 — Barometric Pressure Too Low

Severity: medium Drive with care, to a shop

What P0129 means

The engine control module measures atmospheric pressure with a BARO sensor, or with the MAP sensor at key-on and at wide-open throttle. P0129 sets when that reading is lower than expected for the conditions and altitude. The ECM uses this value to adjust fuel delivery, spark timing and boost or EGR control.

Symptoms

  • Check Engine light on
  • Hesitation or reduced power on acceleration
  • Worse fuel economy
  • Rough idle
  • Possible stalling at idle
  • Odd behavior when altitude changes

Possible causes

  1. Failed barometric pressure sensor or combined MAP/BARO sensor
  2. Corroded, open or shorted wiring or connector at the sensor
  3. Intake air or vacuum leaks
  4. Clogged air filter or restricted intake
  5. ECM software calibration error
  6. Rare ECM hardware fault

How to diagnose

  1. Scan all codes and freeze-frame data, and note any related MAP, MAF or throttle codes.
  2. Inspect the sensor connector and harness for moisture, corrosion, chafing and damaged locking tabs.
  3. With key on and engine off, compare the scan tool pressure reading with the actual local barometric pressure.
  4. Test the sensor's 5 V reference, ground and signal wires with a multimeter, and check the harness continuity to the ECM.
  5. Inspect the intake path: ducts, boots, vacuum hoses, intake manifold gasket and air filter.
  6. Compare MAP and BARO readings at different loads, including wide-open throttle.
  7. Check for ECM software updates for your model.

Common fixes

  • Replace the BARO or combined MAP/BARO sensor
  • Repair the wiring harness and clean or replace the connector
  • Fix intake and vacuum leaks and replace damaged hoses or ducts
  • Replace a clogged air filter
  • Reflash or replace the ECM if everything else checks out

Questions and answers

Can I drive with a P0129 code?

Usually yes, but only briefly and carefully. The engine may run with an inaccurate mixture, lose power and use more fuel, so don't put off diagnosis.

What most often causes P0129?

Most often it's a failed BARO or MAP sensor, or a poor connection in its connector or wiring. Intake air leaks are also worth checking.

Can I just clear the P0129 code?

You can, but it will return if the cause isn't fixed. Find and repair the fault first, then clear the codes.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.