P1119

What Does Code P1119 Mean?

DTC P1119, primarily recognized as a manufacturer-specific or enhanced code, signifies an issue within the Manifold Absolute Temperature (MAT) sensor circuit, specifically indicating a “High Input” condition. The Engine Control Module (ECM) or Powertrain Control Module (PCM) monitors the voltage signal from the MAT sensor to determine the temperature of the air within the intake manifold. This sensor is typically a thermistor, a resistor whose resistance changes predictably with temperature. As the air temperature decreases, the sensor’s resistance increases, causing the voltage signal returned to the ECM to rise. Conversely, as temperature increases, resistance decreases, and the voltage signal drops.

A “High Input” condition for P1119 means the ECM is receiving a voltage signal from the MAT circuit that is abnormally high, exceeding its predetermined maximum operating parameters. This often translates to the ECM interpreting the manifold air temperature as extremely cold (e.g., -40°C or -40°F), or it can signify an open circuit within the sensor or its wiring. The MAT sensor’s data is critical for calculating air density, which directly impacts fuel delivery (fuel trim), ignition timing, and idle speed control to optimize combustion efficiency and reduce emissions. An erroneous, persistently high voltage signal will lead the ECM to incorrect air density calculations, resulting in an improperly rich or lean air-fuel mixture, depending on the ECM’s failsafe strategy.

Common Symptoms

• Malfunction Indicator Lamp (MIL) Illumination: The “Check Engine” light will be illuminated on the dashboard.
• Rough Idle or Stalling: Especially noticeable during cold starts when the ECM is heavily relying on temperature data for fuel enrichment.
• Decreased Fuel Economy: The ECM may command an overly rich fuel mixture due to misinterpreting the air temperature.
• Reduced Engine Performance: Including a lack of power, poor acceleration, and hesitation during driving.
• Black Smoke from Exhaust: Indicating an excessively rich air-fuel mixture.
• Hard Starting: Particularly in colder weather, as incorrect temperature data leads to improper fuel delivery.
• Inconsistent Engine Operating Temperature: Due to improper fuel mapping affecting combustion efficiency.

What Causes the Code P1119?

• Faulty Manifold Absolute Temperature (MAT) Sensor: An internal open circuit, short, or degradation within the thermistor element of the sensor itself.
• Open Circuit in the MAT Sensor Signal Wire: A break or discontinuity in the wiring from the MAT sensor to the ECM/PCM, preventing the signal from reaching the control module.
• Open Circuit in the MAT Sensor Ground Wire: A break in the ground return path for the sensor, preventing a complete circuit and causing a high voltage reading.
• Corroded or Loose Electrical Connectors: Poor terminal contact or high resistance at the MAT sensor connector or the ECM/PCM harness connector due to corrosion, dirt, or improper seating.
• Short to Voltage in the MAT Sensor Signal Circuit: While less common for a “high input” specifically, a signal wire inadvertently contacting a constant voltage source could generate an out-of-range high signal.
• Faulty Engine Control Module (ECM/PCM): Although rare, an internal fault within the ECM/PCM affecting the MAT sensor input circuit could be the cause, but this should only be considered after all other possibilities have been meticulously ruled out.

How to Diagnose and Troubleshoot

Diagnosis of P1119 requires a systematic approach, utilizing a digital multimeter (DMM) and an OBD-II scanner.

1. Visual Inspection:
   • Begin with a thorough visual inspection of the MAT sensor, its wiring harness, and connectors. Look for obvious signs of damage, such as frayed or chafed wires, melted insulation, corrosion at the terminals, or loose connections.
   • Ensure the MAT sensor is securely mounted in the intake manifold or air tract.
2. OBD-II Scanner Live Data Analysis:
   • Connect an OBD-II scanner and retrieve any pending or stored Diagnostic Trouble Codes (DTCs). Note down any other codes present, as they may provide additional context.
   • Access the live data stream and monitor the Intake Air Temperature (IAT) or Manifold Air Temperature (MAT) parameter.
   • With the engine cold and off, compare the IAT/MAT reading to the Ambient Air Temperature (AAT) and Engine Coolant Temperature (ECT) readings. All three should be relatively close (within a few degrees). A MAT reading of -40°C (-40°F) or a significantly fixed, out-of-range high positive temperature is a strong indicator of an open circuit or faulty sensor.
3. Digital Multimeter (DMM) Testing:
   • MAT Sensor Resistance Test: Disconnect the MAT sensor electrical connector. Using the DMM set to ohms, measure the resistance across the two sensor terminals. Consult the vehicle’s service manual for the specified resistance values at various temperatures. Typically, an open circuit (infinite resistance) or resistance significantly outside the specified range indicates a faulty sensor. You can gently warm the sensor with a heat gun (carefully) and observe if the resistance changes predictably.
   • Reference Voltage Test: With the ignition ON (engine OFF) and the MAT sensor disconnected, use the DMM set to volts DC. Place the positive lead on the sensor’s 5-volt reference terminal (refer to wiring diagrams for pinout) and the negative lead on a known good chassis ground. You should read approximately 5 volts.
   • Ground Circuit Continuity Test: With the ignition OFF and the MAT sensor disconnected, use the DMM set to ohms. Place one lead on the sensor’s ground terminal and the other lead on a known good chassis ground. You should read very low resistance (close to 0 ohms). An open circuit (infinite resistance) indicates a problem with the ground wire.
   • Signal Wire Continuity and Short Check: Disconnect both the MAT sensor connector and the ECM/PCM harness connector. Using the DMM set to ohms, measure the resistance between the MAT signal wire terminal at the sensor connector and its corresponding pin at the ECM/PCM connector. Resistance should be very low (continuity). Then, check for continuity between the signal wire and a known good chassis ground, and between the signal wire and battery voltage. Both should show infinite resistance (no short).
4. Wiggle Test: With the OBD-II scanner connected and monitoring live MAT data, gently wiggle the MAT sensor connector and the associated wiring harness. Observe if the MAT reading fluctuates or if the code changes status, indicating an intermittent connection issue.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are commonly recommended:

• Replace the Manifold Absolute Temperature (MAT) Sensor: If the sensor itself fails the resistance test (open circuit or out-of-spec readings), replacing the MAT sensor is the most frequent and direct solution. Ensure the replacement sensor is an OEM equivalent or meets manufacturer specifications for accuracy and fitment.
• Repair or Replace Damaged Wiring: If diagnostic steps reveal an open circuit in the signal or ground wire, the damaged section of the harness must be repaired. Utilize proper wiring repair techniques, such as soldering and using heat-shrink tubing, or replace the affected harness segment if the damage is extensive or difficult to repair reliably.
• Clean and Secure Electrical Connectors: For issues related to corrosion or loose connections, clean the affected connector terminals thoroughly with electrical contact cleaner. Use a small pick or terminal tool to carefully tighten any splayed or loose terminals. Apply dielectric grease to the terminals before reassembly to prevent future corrosion and ensure a robust connection.
• Address Any Short to Voltage: If a short to voltage was identified in the signal circuit, trace the wire meticulously to locate the point of contact with the voltage source and repair the insulation or reroute the wiring as necessary to prevent future contact.
• ECM/PCM Replacement (Last Resort): Only consider replacing the ECM/PCM after all other diagnostic avenues have been exhausted and a fault within the module itself has been definitively confirmed by a specialized technician using advanced diagnostic equipment. This is a rare occurrence for P1119.

After performing any repairs, clear the DTC P1119 from the ECM/PCM using the OBD-II scanner. Then, conduct a comprehensive test drive under varying engine loads and speeds to confirm that the repair is successful and the code does not reappear. Monitoring live data during the test drive can provide immediate feedback on the MAT sensor’s operational integrity.