P1105
SubaruP1105 Subaru: Dual Alternator Upper Fault indicates an issue detected in the upper circuit of the vehicle's dual alternator system, suggesting a voltage or communication discrepancy with the engine control module (ECM).
High SeverityThis code signifies a problem within the dual alternator system's upper circuit, meaning the vehicle's electrical charging system may not be functioning correctly. As a result, the battery may not receive adequate charge, potentially leading to a dead battery and vehicle breakdown.
⚠️ Before You Begin (Safety First)
Working with the charging system can be dangerous. Always disconnect the negative battery terminal before inspecting or repairing components. Wear appropriate eye protection and gloves. Avoid contact with hot engine components and high-voltage wiring.
Common Symptoms
- Battery warning light illuminated on the dashboard
- Dimming headlights or interior lights
- Slow engine cranking or difficulty starting
- Malfunctioning electrical accessories
- Engine stalling at low speeds
Common Causes
- Faulty dual alternator unit
- Damaged or corroded wiring or connectors in the upper alternator circuit
- Failed voltage regulator (often integrated with the alternator)
- Blown fuses related to the alternator circuit
- Issues with the ECM receiving incorrect voltage signals
Frequently reported on: Subaru Outback (2000-2004 H6 models), Subaru Legacy (2000-2004), Subaru Forester (2000-2005), Subaru Baja (2003-2006)
Diagnostic Steps
- Visually inspect both alternators and their wiring harnesses for any obvious signs of damage, loose connections, or corrosion. Check for frayed wires or burnt smells.
- Verify battery voltage with the engine off (should be around 12.6 volts) and then with the engine running (should be 13.5-14.7 volts). A reading outside this range indicates a charging system fault.
- Test the main fuses and fusible links associated with the alternators and charging system using a multimeter for continuity.
- If accessible and safe, check the voltage output from each alternator. Consult your vehicle's service manual for specific testing procedures and expected voltage readings.
- If a specific alternator is suspected, consider having it professionally bench-tested at an auto parts store.
👨🔧 When to Call a Professional
If diagnostic steps confirm a complex wiring issue, or if multiple charging system components test positive for faults, it is advisable to consult a professional technician. Dual alternator systems can be intricate, and misdiagnosis can lead to further electrical damage.
Commonly Asked Questions
What does 'Dual Alternator Upper Fault' specifically mean for my Subaru?
This code indicates that the engine control module (ECM) has detected an issue with the voltage or signal from the upper circuit of one of your vehicle's two alternators, impacting the overall charging system.
Can I drive my Subaru with a P1105 code?
It is not recommended to drive for extended periods with this code. A fault in the dual alternator system can lead to insufficient battery charging, potentially leaving you stranded with a dead battery.
How can I tell which alternator is faulty?
Diagnosing which specific alternator is at fault usually requires testing the output of each unit individually with a multimeter while the engine is running, or having them bench-tested.
Is this code always an alternator replacement?
Not necessarily. While a faulty alternator is a common cause, the code could also point to wiring issues, a bad voltage regulator, or a blown fuse affecting the alternator's circuit. Thorough diagnosis is key.
Are dual alternators common in Subarus?
Dual alternator systems are relatively uncommon in standard passenger Subarus and are usually found in specific heavy-duty, fleet, or older models that required additional electrical capacity.