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DTC codes / Honda codes / P1108

P1108 · HondaBARO Circuit High Input

P1108 on a Honda means the engine computer (ECM/PCM) has detected a voltage signal from the Barometric Pressure (BARO) sensor that is higher than the normal range for the current conditions. The BARO sensor measures atmospheric pressure, and a high input tells the computer the car is at a much lower altitude than it actually is, which can skew fuel delivery and other calculations.

SystemPowertrain
Code typeHonda specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Check Engine Light (MIL) illuminated on the dashboard.
  • Often no symptoms besides the warning light, especially in mild weather or at moderate altitudes.
  • Rough idle or unstable engine operation in some cases.
  • Poor fuel economy or a rich-running condition noticed over time.
  • Hesitation or reduced power during acceleration, particularly at higher altitudes.
  • In rare cases, the engine may stall or run poorly when the BARO signal is far outside the expected range.

Common causes, most likely first

  1. Faulty BARO sensor (internal short or signal circuit fault causing a high voltage output).
  2. Open or high-resistance ground circuit at the BARO sensor, causing the signal voltage to float high.
  3. Damaged or corroded wiring between the BARO sensor and the ECM/PCM, including a short to voltage on the signal line.
  4. Poor electrical connection at the BARO sensor connector or ECM/PCM connector.
  5. ECM/PCM internal fault (less common, but possible if all external circuits test good).
  6. Contamination or blockage at the BARO sensor pressure port (if the sensor is a separate unit exposed to atmosphere).
  7. Aftermarket or incorrect sensor installed previously that does not match Honda specifications.

How to diagnose and fix it

  1. Connect a scan tool and read live data for BARO voltage and calculated altitude; compare with actual atmospheric pressure for your location.
  2. Visually inspect the BARO sensor, its connector, and the wiring harness for damage, corrosion, or loose pins.
  3. Measure reference voltage (usually 5V) and ground continuity at the BARO sensor connector with the key on and engine off.
  4. Backprobe the signal wire at the sensor and at the ECM/PCM to check for a high voltage that does not change with altitude simulation (e.g., using a vacuum pump if applicable).
  5. Check for continuity and resistance on the ground circuit between the sensor and the ECM/PCM; repair any excessive resistance.
  6. If wiring and connections are good, substitute a known-good BARO sensor and recheck live data to see if the high input resolves.
  7. If the code persists with a known-good sensor and verified circuits, diagnose the ECM/PCM for internal faults before replacement.

What a high BARO reading really tells you

  • A high BARO voltage often means the sensor ground circuit is open or resistive, not that the sensor itself has failed; always check grounds before condemning the sensor.
  • Honda BARO sensors are sometimes integrated into the Mass Air Flow (MAF) sensor or the ECM/PCM on certain models, so the repair path can differ significantly by year and engine.
  • The ECM/PCM may use BARO as a backup for other sensors; a high BARO input can cause misleading fuel trim readings and set related codes like P0108 or P2228 if not addressed.
  • Altitude simulation with a vacuum pump is a reliable way to verify BARO sensor operation, but only if the sensor is a standalone unit with a vacuum port; many Honda BARO sensors are sealed and must be tested electrically.
  • A poor connection at the ECM/PCM connector can mimic a failed sensor, so always wiggle-test the harness while watching live BARO data before replacing parts.

Can I keep driving with P1108?

You can usually continue driving with P1108 because the engine will run on default values, but avoid sustained high-speed driving or heavy loads until the fault is repaired. If you notice rough running, stalling, or a significant loss of power, have the vehicle checked promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Honda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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