P1109
HondaIAT - B Sensor Intermittent
Medium SeverityThe Powertrain Control Module (PCM) has detected an inconsistent or erratic signal from the Intake Air Temperature (IAT) Sensor B. This intermittent reading can lead to inaccurate fuel mixture calculations, potentially causing issues with engine performance and reduced fuel efficiency.
⚠️ Before You Begin (Safety First)
Always allow the engine to cool down before working on it, and disconnect the negative battery terminal to prevent accidental shorts or electrical shocks. Be cautious of hot engine components and moving parts.
Common Symptoms
- Check Engine Light illuminated
- Reduced fuel economy
- Rough idle or stalling
- Engine hesitation during acceleration
- Difficulty starting the engine (less common)
Common Causes
- Faulty IAT Sensor B
- Corroded or loose electrical connector for the IAT Sensor B
- Damaged or frayed wiring in the IAT sensor circuit
- Less commonly, an issue with the Powertrain Control Module (PCM) itself
Frequently reported on: Honda Civic (2001-2011), Honda Accord (2003-2012), Honda CR-V (2002-2011), Honda Pilot (2005-2015)
Diagnostic Steps
- Use an OBD-II scanner to confirm P1109 and check for any other related codes.
- Visually inspect the IAT Sensor B and its electrical connector for any signs of damage, corrosion, or loose connections.
- Carefully check the wiring leading to the IAT Sensor B for any cuts, fraying, or pinches.
- If possible, use a multimeter to test the resistance of the IAT Sensor B at various temperatures and compare it to factory specifications.
- If the sensor is deemed faulty or wiring is damaged, replace the IAT Sensor B or repair the wiring as needed.
- Clear the fault code with an OBD-II scanner and perform a test drive to ensure the repair is successful and the code does not return.
👨🔧 When to Call a Professional
If after replacing the IAT Sensor B and inspecting the wiring, the P1109 code returns or symptoms persist, it's advisable to consult a professional mechanic. The issue could be more complex, potentially involving the engine control unit (ECU) or a hard-to-find wiring fault.
Commonly Asked Questions
What is the <strong>IAT Sensor B</strong> and where is it located?
The IAT Sensor B measures the temperature of the air entering the engine. Its exact location can vary, but it's typically found in the intake manifold, air intake duct, or sometimes integrated into the MAF sensor on some Honda models.
Can I drive my Honda with a P1109 code?
While you can usually drive with this code, it's not recommended for long periods as it can lead to reduced fuel efficiency, increased emissions, and potentially poor engine performance.
Is it possible for a dirty air filter to cause P1109?
A severely restricted or dirty air filter primarily affects air flow, but it's unlikely to directly cause an intermittent IAT sensor reading. The issue is more commonly with the sensor or its wiring.
Do I need special tools to replace the IAT Sensor B?
Typically, you'll only need basic hand tools like a socket wrench or screwdriver, and potentially a multimeter for diagnosis. An OBD-II scanner is essential for confirming and clearing the code.
What's the difference between IAT Sensor A and B?
On some vehicles, Sensor A might refer to an IAT sensor before the turbo/supercharger or one directly in the air intake, while Sensor B could be located after the turbo/supercharger or in a different part of the intake manifold to measure air temperature at a different point.