Barometric Pressure Sensor Circuit Low Input
The P0129 code indicates that the engine control module (ECM) has detected a barometric pressure (BARO) sensor signal that is below the expected range. This sensor measures atmospheric pressure to help the ECM adjust fuel delivery and ignition timing. A low reading can cause incorrect air-fuel mixture, leading to poor engine performance, increased emissions, and potential drivability issues.
1. Most Common Causes
- Faulty BARO/MAP sensor (internal open circuit or short to ground)
- Damaged wiring or connector (signal wire shorted to ground)
- Internal PCM failure (rare)
- Blocked atmospheric reference port on the sensor (if combined MAP type)
- PCM software update needed (incorrect altitude calibration)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Poor engine performance (hesitation, stalling)
- Reduced fuel economy
- Rough idle
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to verify the code and check freeze frame data.
Step 2: Inspect the BARO sensor wiring and connector for damage, corrosion, or loose pins.
Step 3: Test the sensor's voltage reference and ground circuits with a multimeter.
Step 4: Compare the sensor's output voltage to actual barometric pressure using a known good sensor or pressure gauge.
Step 5: If sensor is faulty, replace it and clear the code.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally not recommended to drive long distances as the incorrect air-fuel mixture can cause poor performance and potential damage to the catalytic converter.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on the vehicle and shop rates.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.