Comprehensive diagnostic guide for OBD-II P1105 Barometric Pressure Sensor Circuit Malfunction

Important Notes

• OBD-II uses diagnostic trouble codes (DTCs) to indicate issues in powertrain and emissions-related systems. Codes are generated when monitored parameters fall outside expected ranges. This forms the basis for a structured diagnostic approach.
• In general, P-codes under Powertrain Codes indicate issues that affect fueling, ignition timing, and related engine control functions; barometric/ambient pressure sensing can influence fueling calculations.

What This Code Means

• P1105: Barometric pressure sensor circuit malfunction (often described as a defective barometric pressure sensor circuit). In many vehicles, this is tied to the MAP/barometric sensor network used by the PCM to adjust fueling, particularly with altitude and ambient pressure changes.

Symptoms

• Check Engine Light (CEL) is on or flashing, with P1105 stored in PCM unless pending.
• Rough idle, hesitation, or irregular engine idle quality.
• Poor throttle response or reduced acceleration, especially during load changes or at varying elevations.
• Elevated or erratic fuel trims (short-term or long-term fuel trim values out of normal range).
• Noticeable drop in fuel economy or inconsistent running as the sensor reading diverges from actual ambient pressure.
• In some cases, emissions test failure due to improper air/fuel calibration.

Key safety and diagnostic prerequisites

• Ensure you have a current, valid diagnostic scan tool to read live data and freeze-frame data.
• When working with sensors and wiring, follow standard safety practices: engine off, key out, and battery disconnected if you'll be unplugging sensors or wiring. Reconnect and clear codes only after repairs and a verified test drive.
• If you're not sure about the exact sensor topology on a given vehicle (standalone barometric sensor vs. MAP sensor with baro input, etc.), consult the specific service manual for that make/model.

Step-by-Step Diagnosis

Phase 1 - Confirm the issue and gather data

• Verify DTC and freeze-frame data: confirm P1105 is current or pending and note engine rpm, load, air temperature, and any related fuel trim data from the freeze-frame snapshot.
• Check for nearby or related codes (e.g., P0106-P0109 MAP/MAF sensor range/circuit faults). P1105 can be accompanied by other sensor faults, depending on the system design.

Phase 2 - Visual inspection and basic wiring checks

• Inspect the barometric/MAP sensor and its wiring harness for: damaged insulation, corroded or bent pins, loose connectors, and moisture intrusion.
• Check the electrical harness for chafing, harness routing near hot or moving components, or signs of previous repair that might have introduced intermittent connections.
• Inspect sensor mounting and any vacuum/vapour lines (where applicable) for leaks or loose connections that could cause abnormal sensor readings indirectly.

Phase 3 - Sensor and circuit testing (general approach)

• Reference voltage and ground:
  • With ignition on (engine off or at idle as appropriate to the vehicle), check that the MAP/barometric sensor has a stable reference voltage (commonly around 5V or 3.3V) and a solid ground.
  • Check for excessive resistance or an open circuit between the sensor ground and PCM ground.
• Signal circuit check:
  • Measure the sensor output signal voltage with a DMM or oscilloscope. Compare the signal range to the vehicle's service information for expected values (these vary by vehicle; consult the manual).
  • If the sensor output is flatlined, erratic, or out of range, suspect the sensor or its wiring.
• Compare MAP vs. ambient/barometric readings:
  • Some vehicles provide a separate barometric pressure reading (baro) and a MAP reading. If the baro pressure reading is unavailable or stuck, P1105 can occur.
  • If possible, compare readings from the scanner (MAP/baro) against known ambient pressure (e.g., local altitude/sea level data) to see if readings track environmental changes.
• Vacuum/pressure path inspection:
  • Check for vacuum leaks around intake manifold, vacuum hoses, and inlets that could cause abnormal MAP/baro readings or affect air density measurements used by the PCM.

Phase 4 - Functional tests and cross-checks

• Live data drive test:
  • With the scan tool, observe MAP or barometric pressure readings during a controlled drive (idle, light throttle, acceleration, deceleration, and under load). Watch for readings that are stale, out of range, or not changing with altitude/temperature changes.
  • If readings do not change with altitude or ambient pressure changes, this strongly suggests a sensor or wiring fault rather than a transient engine issue.
• If sensor wiring and sensor itself appear sound, test with a known-good sensor if feasible (swap test or functional replacement) to confirm fault isolation.
• ECU/PCM fault consideration:
  • If the sensor and wiring check out but DTC persists, consider a PCM fault or a need for calibration/updates per the vehicle manufacturer's guidelines. A PCM fault would be less common but must be considered when no sensor/wiring fault is found.

Phase 5 - Confirm repair and verify

• If a faulty sensor is identified and replaced:
  • Clear the DTCs and perform a thorough test drive under a range of engine loads, speeds, and ambient conditions to ensure the code does not return.
• If the wiring or connectors were the issue:
  • Repair or replace damaged harness segments, ensure proper connector seating, and apply dielectric grease as appropriate for the connector type.
• If no sensor or wiring fault is found and the code persists:
  • Revisit the vehicle's service documentation for OEM specs. Consider PCM fault or calibration requirements, and re-check other related sensors for any cascading issues that could cause the PCM to misinterpret readings.

Probable Causes

• Barometric/MAP sensor fault (sensor itself or the signal path): 40-60%
• Wiring harness/connectors/connectivity issues (corrosion, loose pins, damaged insulation): 20-35%
• Vacuum leaks or intake system anomalies that indirectly affect sensor readings: 5-15%
• PCM/ECU fault or require software calibration/update: 5-10%
• Ambient environmental conditions causing sensor saturation or misreads (less common as a sole cause): 0-5%

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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