P1107
SubaruDual Alternator Lower Circuit Malfunction/ Manifold Absolute Pressure (MAP) Sensor Circuit Intermittent Low Voltage
Medium SeverityThis Subaru-specific code indicates a malfunction in either the dual alternator's lower circuit or an intermittent low voltage reading from the Manifold Absolute Pressure (MAP) sensor. Depending on the root cause, drivers may experience issues with the vehicle's charging system or engine performance, potentially leading to reduced power and fuel efficiency.
⚠️ Before You Begin (Safety First)
Always prioritize safety when working on your vehicle. Ensure the engine is off and cool, and disconnect the battery's negative terminal before inspecting any electrical components or sensors to prevent accidental shorts or shocks. Be cautious of hot engine parts and rotating components.
Common Symptoms
- Check Engine Light (CEL) illuminated
- Rough idle or stalling
- Poor acceleration or reduced engine power
- Decreased fuel economy
- Battery warning light (if alternator related)
- Dimming headlights or interior lights (if alternator related)
- Difficulty starting the vehicle (if alternator related)
Common Causes
- Faulty Manifold Absolute Pressure (MAP) sensor
- Damaged or corroded wiring in the MAP sensor circuit
- Loose or corroded electrical connector for the MAP sensor
- Vacuum leak affecting the MAP sensor reading
- Malfunction in the dual alternator lower circuit (if equipped)
- Blown fuse related to the charging system or MAP sensor
- Issues with the Powertrain Control Module (PCM)
Frequently reported on: Subaru Outback 2005-2009, Subaru Legacy 2006-2010, Subaru Forester 2008-2013, Subaru Impreza 2007-2011, Subaru Tribeca 2006-2009
Diagnostic Steps
- Retrieve all stored trouble codes to check for related issues.
- Visually inspect the wiring and connectors leading to the MAP sensor for any signs of damage, corrosion, or looseness.
- Examine the vacuum hose connected to the MAP sensor for cracks, leaks, or disconnections.
- If your vehicle has a dual alternator system, visually inspect the wiring and connections for the lower alternator circuit.
- Check all relevant fuses in the engine bay and under the dashboard that relate to the engine management system or charging system.
- If comfortable, use a multimeter to test the voltage at the MAP sensor connector (refer to your vehicle's service manual for specific values).
- Clear the P1107 code and test drive the vehicle to see if the code returns.
👨🔧 When to Call a Professional
If basic diagnostic steps, such as checking connections and fuses, do not resolve the P1107 code, or if you suspect a complex electrical issue with the dual alternator system, it is highly recommended to consult a professional Subaru mechanic. Specialized tools and advanced electrical diagnostic skills are often required for accurate troubleshooting.
Commonly Asked Questions
What is a MAP sensor and why is it important?
The Manifold Absolute Pressure (MAP) sensor measures the pressure inside your engine's intake manifold. This information is crucial for the engine control unit to calculate engine load and adjust fuel delivery and ignition timing, impacting performance and fuel efficiency.
Can I drive my Subaru with a P1107 code?
While it might be possible to drive short distances, it's not recommended. A P1107 code could lead to poor engine performance, reduced fuel economy, or issues with the charging system, which could eventually leave you stranded or cause further damage.
How do I test the MAP sensor myself?
You can test the MAP sensor by checking its voltage output with a multimeter while the engine is running and at different RPMs. You would typically look for a stable voltage reading that changes predictably with engine vacuum. Consult your vehicle's service manual for the correct voltage specifications for your specific Subaru model.
What if my Subaru has a dual alternator? How does that relate to P1107?
Some heavy-duty or specific Subaru models might feature a dual alternator system for increased electrical demands. A malfunction in the lower circuit of this system could trigger P1107. Diagnosis would involve checking the alternator's output, wiring, and associated fuses.
After fixing the issue, how do I turn off the Check Engine Light?
Once the underlying problem causing the P1107 code has been repaired, you can clear the Check Engine Light using an OBD-II scan tool. If you don't have one, disconnecting the negative battery terminal for 15-30 minutes can sometimes clear codes, but this will also reset other vehicle settings.