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DTC codes / Mercedes-Benz codes / P1105

P1105 · Mercedes-BenzAtmospheric Pressure Sensor In Control Module

P1105 on Mercedes-Benz vehicles indicates that the engine control module (ECM) has detected a fault in its internal atmospheric pressure sensor circuit, which is used to calculate air density and adjust fuel delivery. The ECM compares this sensor's output against expected values and sets the code when the signal is out of range or implausible.

SystemPowertrain
Code typeMercedes-Benz specific
SeverityMedium
Fix difficultyProfessional
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • Rough idle or stumbling, especially at high altitudes
  • Reduced engine performance or hesitation during acceleration
  • Poor fuel economy or rich-running condition
  • In rare cases, the engine may enter limp mode

Common causes, most likely first

  1. Faulty atmospheric pressure sensor integrated into the ECM (internal failure)
  2. Corroded or damaged wiring between the sensor and ECM connector
  3. Water intrusion or contamination inside the ECM housing
  4. Loose or poor ground connection at the ECM
  5. Voltage supply issue to the ECM affecting sensor reference voltage
  6. Software glitch in the ECM requiring reprogramming

How to diagnose and fix it

  1. Use a scan tool to verify the code and check live data for atmospheric pressure reading
  2. Inspect the ECM connector and wiring for corrosion, water damage, or loose pins
  3. Check the ECM ground connections and repair any poor grounds
  4. Perform a voltage drop test on the sensor reference circuit
  5. If wiring and grounds are good, test the sensor output signal with a multimeter
  6. Reprogram or replace the ECM if the internal sensor is confirmed faulty

When the ECM Itself Is the Fault

  • The atmospheric pressure sensor is internal to the ECM on many Mercedes-Benz models, so a code for this sensor often means the ECM itself is failing rather than an external part.
  • Water intrusion into the ECM housing, often from a clogged drain or failed seal, is a common cause that technicians miss when they only check wiring.
  • A weak battery or charging system issue can cause the ECM to set this code intermittently, so always verify battery voltage and charging performance first.
  • This code can be set by a software calibration issue, and a simple ECM reprogramming may resolve it without replacing hardware.
  • Do not confuse this with a mass airflow sensor fault; the atmospheric pressure sensor measures ambient pressure, not intake airflow.

Can I keep driving with P1105?

You can generally continue driving with this code, but avoid sustained high-speed or high-load driving until it is diagnosed, as fuel mixture calculations may be slightly off. If the engine runs rough or enters limp mode, seek service promptly.

Tools that help

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

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