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 lower than the expected range, typically below 0.5 volts or corresponding to an altitude above 10,000 feet. This sensor measures atmospheric pressure to adjust fuel delivery and ignition timing. A low reading can cause the ECM to lean out the air-fuel mixture, leading to poor performance, hesitation, and potential engine damage if not addressed.
01. Most Common Causes
- Faulty barometric pressure sensor
- Open or shorted wiring to the BARO sensor
- Poor electrical connection at the sensor or ECM
- ECM software or hardware failure (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Engine hesitation or surging during acceleration
- Poor fuel economy
- Rough idle or stalling
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to verify the BARO sensor reading; compare to actual atmospheric pressure (e.g., weather report).
Step 2: Inspect the sensor wiring and connector for damage, corrosion, or loose pins.
Step 3: Test the sensor voltage reference (typically 5V) and ground at the sensor connector.
Step 4: If wiring is intact, replace the barometric pressure sensor.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the incorrect air-fuel mixture can cause engine damage, reduced performance, and increased emissions.
How much does it cost to fix?▼
The typical repair cost ranges from $50 to $150, including parts (sensor $20-$60) and labor (0.5-1 hour).