OBD-II Code P0107: Understanding and Resolving Manifold Absolute Pressure Circuit Low Input

The OBD-II trouble code P0107, known as “Manifold Absolute Pressure/Barometric Pressure Circuit Low Input,” indicates a problem within your vehicle’s engine management system. This code is triggered when the Powertrain Control Module (PCM) detects an abnormally low voltage signal from the Manifold Absolute Pressure (MAP) sensor circuit. This sensor is crucial for accurate fuel delivery, and when it malfunctions, it can lead to significant engine performance issues.

Decoding the P0107 Code: Manifold Absolute Pressure Circuit Low Input (H2)

To understand P0107, we need to delve into the role of the MAP sensor. This sensor measures the pressure within the intake manifold, which reflects the engine’s vacuum. The PCM supplies a 5-volt reference signal to the MAP sensor. Inside the sensor, a resistor reacts to pressure changes, altering the voltage that is sent back to the PCM. This voltage typically ranges from about 1 volt at high vacuum (low pressure) to 4.5 volts at low vacuum (high pressure), depending on engine load. The PCM uses this information to calculate air density and adjust fuel delivery accordingly for optimal combustion.

A P0107 code is set when the PCM registers a MAP sensor signal voltage that falls below a critical threshold, usually around 0.25 volts. This “low input” condition signals that the sensor or its circuit is malfunctioning, preventing the PCM from accurately gauging manifold pressure.

Alt text: A close-up of a Manifold Absolute Pressure (MAP) sensor, a vital component in modern vehicle engines, used to measure intake manifold pressure for optimal engine performance.

Common Symptoms Associated with OBD-II Code P0107 (H2)

When the MAP sensor signal is low due to a P0107 fault, your vehicle may exhibit a range of symptoms, primarily affecting engine start and overall performance. These symptoms can vary in severity but should be addressed promptly to prevent further complications:

• Difficulty Starting: A low MAP sensor signal can severely disrupt the air-fuel mixture required for ignition. The engine may struggle to start or require prolonged cranking.
• Extended Cranking Time: Even if the engine eventually starts, you might notice it takes longer than usual to crank. This is because the PCM is receiving incorrect pressure readings, leading to inefficient fuel delivery during startup.
• Engine Sputtering or Misfiring: Inaccurate manifold pressure readings can cause the engine to run erratically. You may experience sputtering, misfires, or hesitation, especially during acceleration.
• Black Smoke from Exhaust: A faulty MAP sensor signal can cause the PCM to incorrectly calculate the air-fuel ratio, often resulting in a rich mixture (too much fuel). This rich condition can lead to incomplete combustion and the emission of black smoke from the exhaust pipe, indicating excessive fuel.
• Reduced Fuel Economy: An imbalanced air-fuel mixture due to a faulty MAP sensor signal forces the engine to work harder and less efficiently, leading to a noticeable decrease in fuel economy.
• Intermittent Engine Stalling: In some cases, a P0107 code can cause the engine to stall unexpectedly, particularly at idle or low speeds. This is due to the PCM’s inability to maintain a stable air-fuel mixture.
• Illuminated Malfunction Indicator Lamp (MIL): The most obvious sign is the illumination of the check engine light or MIL on your dashboard. This light indicates that the PCM has detected a fault and stored the P0107 code.

Potential Causes of a P0107 Code (H2)

Several factors can contribute to a low MAP sensor signal and trigger a P0107 code. Identifying the root cause is crucial for effective repair:

• Faulty MAP Sensor: The MAP sensor itself is a common culprit. Internal sensor failure due to age, contamination, or electrical damage can lead to inaccurate readings and a low voltage signal.
• Signal Circuit Issues: Problems within the signal circuit wiring connecting the MAP sensor to the PCM can disrupt the signal. This includes:
  • Open Circuit: A break in the signal wire, preventing the voltage signal from reaching the PCM.
  • Short to Ground: The signal wire may be shorting to ground, causing the voltage to drop below the acceptable range.
  • Short to Voltage: Less common, but the signal wire could be shorting to another voltage source, though this is more likely to cause a high input code (P0108).
• 5-Volt Reference Circuit Problems: The MAP sensor relies on a stable 5-volt reference signal from the PCM. Issues in this circuit can cause a P0107 code:
  • Open Circuit: A break in the 5-volt reference wire, preventing power from reaching the sensor.
  • Short to Ground: The 5-volt reference wire may be shorting to ground, dropping the voltage supply to the sensor.
• Ground Circuit Issues: The MAP sensor also needs a good ground connection to function correctly. Problems in the ground circuit can include:
  • Open Ground: A break in the ground wire, interrupting the sensor’s ground path.
  • Shorted Ground: While technically redundant, a ground wire fault could also contribute to circuit issues.
• PCM Failure (Rare): In rare instances, a faulty PCM itself can misinterpret sensor signals or have internal issues affecting sensor circuits. PCM failure is usually diagnosed after ruling out all other possibilities.

Diagnosing and Resolving the P0107 Code (H2)

Diagnosing a P0107 code requires a systematic approach, starting with basic checks and progressing to more in-depth testing. Here’s a step-by-step guide for troubleshooting:

1. Initial Scan Tool Monitoring (H3)

   • Connect a scan tool to your vehicle’s OBD-II port.
   • Turn the ignition key to the “ON” position (engine off).
   • Monitor the MAP sensor voltage reading on the scan tool. A normal reading with the key on, engine off, is typically around 4-5 volts (atmospheric pressure).
   • If the reading is below 0.5 volts, suspect a circuit issue or sensor fault.

2. 5-Volt Reference Circuit Test (H3)

   • Turn the engine off and disconnect the MAP sensor electrical connector.
   • Use a Digital Volt-Ohm Meter (DVOM) to check for 5 volts on the 5-volt reference circuit pin in the MAP sensor connector (consult your vehicle’s wiring diagram for pin identification).
   • If 5 volts is absent, check for the 5-volt reference at the PCM connector.
     • If 5 volts is present at the PCM connector but not at the MAP sensor connector, repair the open circuit in the reference wire between the PCM and MAP sensor.
     • If 5 volts is absent at the PCM connector, investigate PCM power and ground supply. Repair or replace the PCM as necessary (after checking PCM power and ground).
     • Note for Chrysler Vehicles: On Chrysler vehicles, a shorted sensor on the 5-volt reference circuit (like a crank sensor or vehicle speed sensor) can pull down the voltage. Disconnect sensors one by one until the 5-volt reference reappears to identify the shorted sensor.

3. Signal Circuit Test (H3)

   • If the 5-volt reference is present at the MAP sensor connector, use a jumper wire to connect the 5-volt reference pin to the signal pin in the MAP sensor connector.
   • Monitor the MAP sensor voltage on the scan tool. It should now read approximately 4.5 to 5 volts.
   • If the voltage reading is correct (high), replace the MAP sensor, as the sensor itself is likely faulty.
   • If the voltage reading remains low, suspect a problem in the signal circuit wiring between the MAP sensor and the PCM. Repair any open or short circuits in the signal wire and retest.

4. Wiggle Test (H3)

   • Reconnect the MAP sensor and start the engine.
   • Gently wiggle and manipulate the MAP sensor wiring harness and connector.
   • Tap lightly on the MAP sensor itself.
   • Observe the scan tool reading for any changes in MAP sensor voltage or engine RPM.
   • If wiggling or tapping causes fluctuations, suspect a loose connection, damaged wiring, or a faulty sensor connector. Repair or replace the affected components.

5. Vacuum Test (H3)

   • With the engine running and scan tool connected, use a vacuum pump (or carefully apply vacuum with a hose) to the MAP sensor vacuum port.
   • As vacuum is applied, the MAP sensor voltage reading on the scan tool should decrease.
   • With no vacuum applied (atmospheric pressure), the MAP sensor should read approximately 4.5 volts.
   • If there is no change in the MAP sensor reading as vacuum is applied, the MAP sensor is likely faulty and needs replacement.

Related OBD-II Codes (H2)

Several other OBD-II codes are related to the MAP sensor and intake manifold pressure readings. Understanding these codes can provide further context during diagnosis:

• P0105: MAP/Barometric Pressure Circuit Malfunction
• P0106: MAP/Barometric Pressure Circuit Range/Performance Problem
• P0108: MAP/Barometric Pressure Circuit High Input
• P0109: MAP/Barometric Pressure Circuit Intermittent

Need More Assistance with P0107? (H2)

Diagnosing automotive issues can be complex. If you require further assistance with a P0107 trouble code, we encourage you to post your question in our FREE car repair forums. Our community of experienced technicians and enthusiasts is ready to provide guidance and support.

Disclaimer: This information is for informational purposes only and should not be considered professional repair advice. We are not responsible for any actions taken on your vehicle based on this information. Always consult a qualified technician for diagnosis and repair.