P1109
GMIntake Air Temperature (IAT) Sensor B Circuit Intermittent
Medium SeverityThe P1109 code indicates an intermittent signal from the Intake Air Temperature (IAT) Sensor B, which the engine control module (ECM) uses to calculate proper fuel delivery. This inconsistency can lead to improper air/fuel mixture, potentially affecting engine performance and fuel efficiency.
⚠️ Before You Begin (Safety First)
Always work on a cool engine. Disconnect the negative battery terminal before performing any electrical repairs to prevent accidental shorts or injury. Use appropriate personal protective equipment.
Common Symptoms
- Check Engine Light illuminated
- Rough idle
- Poor fuel economy
- Reduced engine performance
- Difficulty starting the engine
Common Causes
- Faulty or failing Intake Air Temperature (IAT) Sensor B
- Loose or corroded electrical connector at the IAT sensor
- Damaged or frayed wiring in the IAT sensor circuit
- Intermittent open or short in the IAT sensor wiring
- Rarely, a faulty Engine Control Module (ECM)
Frequently reported on: Chevrolet Silverado (2000-2013), GMC Sierra (2000-2013), Chevrolet Tahoe (2000-2014), Cadillac Escalade (2002-2014), Pontiac Grand Prix (2004-2008)
Diagnostic Steps
- Inspect the IAT sensor B and its electrical connector for any visible damage, corrosion, or loose connections.
- Clean the electrical connector with electrical contact cleaner and ensure a snug fit.
- Check the wiring leading to the IAT sensor for any cuts, frays, or signs of rodent damage.
- If no obvious issues are found, consider testing the IAT sensor resistance with a multimeter (refer to service manual specifications).
- If the sensor tests faulty or shows intermittent readings, replace the IAT sensor B.
- Clear the diagnostic trouble code (DTC) using an OBD-II scanner and test drive the vehicle to see if the code returns.
👨🔧 When to Call a Professional
If you've replaced the IAT sensor and thoroughly checked wiring, but the P1109 code or symptoms persist, it's best to consult a professional technician to diagnose potential underlying ECM or complex wiring issues.
Commonly Asked Questions
Can I drive with a P1109 code?
While you might be able to drive, it's not recommended for extended periods as it can lead to poor fuel economy and reduced engine performance. It's best to address it promptly.
Where is the IAT sensor B located?
The location can vary by GM model, but it's typically found in the intake manifold, air intake ducting, or sometimes integrated into the mass airflow (MAF) sensor. Consult your vehicle's service manual for the exact location.
How much does an IAT sensor cost?
An IAT sensor is generally inexpensive, usually ranging from $15 to $50, depending on the vehicle and brand.
Do I need special tools to replace an IAT sensor?
Most IAT sensors can be replaced with basic hand tools like a wrench or a socket, and possibly a flathead screwdriver for hose clamps. An OBD-II scanner is needed to clear the code.
Can a dirty air filter cause a P1109 code?
A very restrictive or dirty air filter primarily affects airflow, but it's unlikely to directly cause an intermittent IAT sensor signal. However, it's good practice to ensure your air filter is clean.