P1119
GMP1119 indicates that the Engine Control Module (ECM) has detected a voltage signal from the Manifold Absolute Temperature (MAT) sensor circuit that is higher than the expected operating range. This typically suggests an open circuit or a sensor failure.
Medium SeverityThis code means your vehicle's computer, the Engine Control Module (ECM), is seeing an impossibly high voltage signal from the Manifold Absolute Temperature (MAT) sensor, which it uses to measure the temperature of the air entering the engine. When the ECM doesn't know the accurate air temperature, it struggles to calculate the correct fuel mixture, potentially leading to performance issues and increased emissions.
⚠️ Before You Begin (Safety First)
Always allow the engine to cool down before working on any components. Disconnect the negative battery cable before performing electrical work to prevent accidental shorts or injury. Use appropriate personal protective equipment, such as gloves and eye protection. Never work under a vehicle supported only by a jack. Always use jack stands on a level, firm surface.
Common Symptoms
- Check Engine Light illuminated
- Poor fuel economy
- Rough idle
- Engine hesitation or stumble during acceleration
- Increased exhaust emissions
- Difficulty starting (especially in extreme temperatures)
Common Causes
- Faulty Manifold Absolute Temperature (MAT) sensor
- Open circuit in the MAT sensor signal wire
- Corroded or loose connections at the MAT sensor or ECM
- Damaged wiring harness leading to the MAT sensor
- Less commonly, a failing Engine Control Module (ECM)
Frequently reported on: 2008 Chevrolet Silverado 1500, 2010 GMC Sierra 2500HD, 2007 Cadillac Escalade, 2011 Chevrolet Tahoe, 2009 Pontiac G6
Diagnostic Steps
- First, let's understand why this code sets. A "High Input" means the voltage is above what the ECM expects. For a typical thermistor-style sensor, high voltage usually indicates an open circuit or a very cold temperature reading, but in this context, it's an electrical fault.
- Begin by visually inspecting the Manifold Absolute Temperature (MAT) sensor and its wiring connector. Look for any obvious damage to the wires, frayed insulation, or corrosion on the terminals. This is important because sometimes the simplest problem is overlooked.
- Locate the MAT sensor. On many GM vehicles, it's integrated into the Mass Air Flow (MAF) sensor housing or located in the intake manifold/air ducting. Refer to your vehicle's service manual for its exact location. Understanding where it is helps with troubleshooting.
- With the ignition off and battery disconnected, carefully disconnect the electrical connector from the MAT sensor. Inspect the terminals within the connector for bending, corrosion, or looseness. The connection needs to be solid for proper signal transmission.
- If you have a multimeter, you can perform some basic electrical checks. With the connector disconnected from the sensor (and ignition on, but engine off), check for 5-volt reference voltage and a good ground at the MAT sensor harness connector. An open in the reference or ground circuit can cause this "high input."
- If the wiring appears intact and you have proper reference voltage and ground, the MAT sensor itself is the most likely culprit. Replace the sensor, ensuring you get the correct part for your specific GM model.
- After replacing the sensor, clear the P1119 code using an OBD-II scanner. Then, start the engine and monitor for a few drive cycles to see if the code returns. We want to make sure the fix is permanent.
👨🔧 When to Call a Professional
If you've replaced the sensor and checked the wiring thoroughly but the code persists, or if you're uncomfortable with electrical diagnostics, it's time to consult a professional technician. They have specialized diagnostic tools to test wiring harness integrity and ECM functionality, which can be complex.
Commonly Asked Questions
What is a Manifold Absolute Temperature (MAT) sensor and what does it do?
The MAT sensor, sometimes called an Intake Air Temperature (IAT) sensor, measures the temperature of the air as it enters the engine. This information is critical for the Engine Control Module (ECM) to calculate the correct amount of fuel to inject, ensuring efficient combustion and proper emissions control. Think of it as telling the computer how 'dense' the air is, which changes with temperature.
How does a 'High Input' translate to a problem?
For most temperature sensors, including the MAT sensor, resistance changes with temperature. As temperature increases, resistance decreases, and voltage typically drops. A 'High Input' condition usually means the ECM is seeing an abnormally high voltage, often indicating an open circuit or a problem where the sensor signal isn't returning to the ECM as expected. It's like the sensor is shouting at the top of its lungs when it should be speaking quietly.
Can I drive with a P1119 code?
While you can technically drive with a P1119 code, it's not recommended for long. The engine's fuel mixture will be inaccurate, leading to reduced fuel economy, potential power loss, and increased emissions. This can also cause other components, like the catalytic converter, to work harder and potentially fail prematurely. It's best to address it promptly to avoid compounding problems.
Is the MAT sensor always a separate part?
Not always. On many modern GM vehicles, especially those with Mass Air Flow (MAF) sensors, the MAT (or IAT) sensor is often integrated directly into the MAF sensor housing. So, if your vehicle uses a MAF sensor, you might find that you're replacing the entire MAF unit to fix a MAT sensor issue.
What tools do I need to diagnose and fix P1119?
For diagnosing, you'll definitely want an OBD-II scanner to read and clear codes. A digital multimeter is invaluable for checking voltage and continuity in the wiring. For the repair itself, basic hand tools like sockets, wrenches, and screwdrivers, specific to your vehicle, will likely be needed. Always have your vehicle's service manual handy for precise locations and specifications.