Powertrain, generic · Fuel and air metering

P0129 Barometric Pressure Too Low

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The engine control module needs the ambient air pressure for mixture, altitude correction and boost limits. It comes either from a dedicated barometric sensor or from the MAP sensor, read at key-on with the engine stopped and updated at wide-open throttle. P0129 means this value is lower than physically possible – even on the highest drivable passes air pressure stays around 50 kPa, and GM and Ford use 50 kPa as their lower plausibility limit. Usual causes are a MAP or baro sensor reading too low, a blocked sensor port or high resistance in the wiring. No manufacturer document naming exactly this code was found: GM and Ford file the same finding under P2227.

Likely causes

MAP or baro sensor reading too low (dirty, oiled, drifted)
High resistance or corrosion in signal wire or connector
Sensor port or hose blocked
Control module (baro sensor often built in) or software

Symptoms

  • Check engine light on
  • Rich mixture, higher consumption, rough idle
  • Loss of power (altitude-corrected boost limits)

Repair estimate

DifficultyEasyDIY possible
Parts and labour€20–250
Time0.3–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

barometric pressure sensormanifold absolute pressure sensorsensor wiring

Related codes

P2227P2228P0069P0106P0107

References: law.cornell.edu, gsi.ext.gm.com, fordservicecontent.com, en.wikipedia.org.