P1118
NissanManifold Absolute Temperature Circuit Low Input
Low SeverityThis code means the engine's computer isn't seeing the correct voltage from the sensor that measures how warm the air is going into the engine. When the computer doesn't know the intake air temperature, it can't accurately calculate the right amount of fuel to mix with the air, which can affect how your engine runs.
⚠️ Before You Begin (Safety First)
Remember, safety first when working on any vehicle. Always disconnect the negative battery terminal before working on electrical components to prevent accidental shorts or shocks. Make sure the engine is cool to the touch before handling any sensors or wiring in the engine bay to avoid burns. And always wear eye protection.
Common Symptoms
- Check Engine Light (CEL) illuminated on the dashboard. This is usually the first sign something's off.
- Reduced fuel economy, because the engine might be running too rich or too lean.
- Rough idling, as the engine struggles with an incorrect air-fuel mixture.
- Hesitation or poor acceleration, especially when the engine tries to adjust to changing conditions.
- Difficulty starting the engine, particularly in extreme weather conditions where air temperature is critical.
Common Causes
- A faulty Intake Air Temperature (IAT) sensor itself. These sensors can fail internally, sending an incorrect or no signal.
- Damaged or corroded wiring in the IAT sensor circuit. Low input often points to a short to ground or an open circuit in the signal wire.
- A poor connection at the IAT sensor connector. Always check for bent pins, corrosion, or loose connections.
- Issues with the Engine Control Module (ECM), though this is less common. The ECM might not be reading the signal correctly, or its internal circuitry related to the IAT input could be faulty.
- A short circuit to ground in the sensor's signal wire. This would cause the ECM to see a constant low voltage, triggering the code.
Frequently reported on: Nissan Altima (2007-2012), Nissan Sentra (2007-2012), Nissan Murano (2009-2014), Nissan Titan (2004-2015), Nissan Frontier (2005-2019)
Diagnostic Steps
- First, locate the Intake Air Temperature (IAT) sensor. On many Nissan models, it's integrated into the Mass Air Flow (MAF) sensor, which is typically found in the air intake tube right after the air filter box. If it's separate, it will be in the intake manifold or air intake duct.
- Visually inspect the IAT sensor and its wiring harness. Look for any obvious damage, frayed wires, or corrosion at the connector. Sometimes, simply cleaning the connector can resolve the issue.
- With a multimeter, check the voltage at the IAT sensor connector. You should see a reference voltage (usually 5V) and a ground. This helps you understand if the ECM is sending power to the sensor.
- Next, measure the resistance of the IAT sensor itself (with the connector disconnected). The resistance should change with temperature. If it reads open or shorted, the sensor is likely bad.
- If the sensor tests good, check for continuity in the wiring from the sensor connector back to the ECM connector. This confirms there are no breaks or shorts in the wires.
- If you find a fault with the sensor, replace it. If it's a wiring issue, repair the wiring. After any repairs, clear the code and test drive the vehicle to ensure the issue is resolved.
👨🔧 When to Call a Professional
If you've checked the sensor and wiring and can't find the fault, or if the issue seems to involve the Engine Control Module (ECM), it's definitely time to bring in a seasoned technician. They have advanced diagnostic tools and experience to pinpoint more complex electrical gremlins.
Commonly Asked Questions
What does Manifold Absolute Temperature actually mean?
Good question! The 'Manifold Absolute Temperature' refers to the temperature of the air as it enters the engine's intake manifold. This temperature is crucial because warmer air is less dense than colder air, and the engine's computer needs to know the air density to deliver the correct amount of fuel for efficient combustion. This is the 'why' behind the sensor's importance.
Is it safe to drive with a P1118 code?
While it's generally not an emergency that will leave you stranded immediately, it's not ideal to drive for extended periods with this code. Your engine won't be running as efficiently as it should, which can lead to poorer fuel economy, increased emissions, and over time, potentially impact other engine components due to an incorrect air-fuel mixture. It's best to address it sooner rather than later to prevent further problems and maintain optimal engine health.
How can I test the Intake Air Temperature sensor with a multimeter?
To test the IAT sensor, you'll first need to disconnect its electrical connector. Then, set your multimeter to the ohms (resistance) setting. Touch the probes to the two terminals of the sensor. You should get a resistance reading. The important part is that this resistance value should change as the sensor's temperature changes. For example, if you warm the sensor gently (maybe with a hair dryer, carefully!), the resistance should decrease. If it stays constant, reads extremely high (open circuit), or extremely low (short circuit), the sensor is likely faulty. Always check your vehicle's service manual for specific resistance values at different temperatures.
Can a dirty air filter cause a P1118 code?
That's a good thought, but typically, a dirty air filter itself won't directly cause a P1118 code. A dirty air filter restricts airflow, which usually impacts the Mass Air Flow (MAF) sensor readings and overall engine performance. However, if the IAT sensor is integrated into the MAF sensor, and the MAF sensor housing gets very dirty, it could potentially affect the IAT reading indirectly. But for a direct P1118, we're almost always looking at the IAT sensor, its wiring, or its connection.
What happens if I ignore this code?
If you ignore the P1118 code, the main consequence is that your engine will continue to operate with an inaccurate intake air temperature reading. This means the Engine Control Module (ECM) will be making fuel delivery decisions based on incorrect data, leading to a suboptimal air-fuel mixture. This can manifest as reduced fuel economy, increased exhaust emissions, potentially poorer engine performance, and even a slightly rougher idle. While it might not stop your car from running, it's like trying to bake a cake without knowing the oven temperature perfectly; you might get by, but the results won't be ideal and could lead to other issues over time.