P1108
SubaruIndicates a malfunction in the circuit responsible for illuminating the battery warning lamp, often associated with dual alternator systems or the primary charging system feedback.
Medium SeverityThis code signifies an electrical issue within the circuit that controls your vehicle's battery warning light. While the alternator might still be charging, a malfunction in this circuit prevents the driver from being properly warned of potential charging system failures, which could lead to a dead battery or stranded vehicle.
⚠️ Before You Begin (Safety First)
Always disconnect the negative battery terminal before inspecting electrical components to prevent accidental shorts or shocks. Allow components to cool before handling.
Common Symptoms
- Battery warning light does not illuminate during ignition key on (engine off) self-test
- Battery warning light remains off even if a charging system fault is present
- Intermittent or flickering battery warning light
- Other charging system warning lights or messages may appear (if applicable)
Common Causes
- Burnt out battery warning lamp bulb (in older instrument clusters)
- Faulty wiring or connector in the battery lamp circuit
- Malfunctioning instrument cluster
- Problem with the alternator's lamp circuit output
- Issue with the Engine Control Unit (ECU) or Body Control Module (BCM) if it controls the lamp directly
Frequently reported on: Subaru Outback (2000-2009), Subaru Forester (1998-2008), Subaru Impreza (1997-2007), Subaru Legacy (1995-2004)
Diagnostic Steps
- Check the instrument cluster fuses for any blown fuses related to the dashboard lights.
- If accessible and applicable, inspect the battery warning lamp bulb for being burnt out and replace if necessary.
- Visually inspect the wiring and connectors leading to the instrument cluster and alternator for any signs of damage, corrosion, or looseness.
- Using a multimeter, test for continuity and proper voltage in the battery lamp circuit if you have a wiring diagram.
- Clear the code and re-check if the warning light functions correctly.
👨🔧 When to Call a Professional
If, after basic checks, the battery warning light remains inoperative, or if you suspect an underlying charging system issue, it is best to consult a professional mechanic. Complex electrical diagnostics require specialized tools and knowledge.
Commonly Asked Questions
What is the battery warning light?
It's an indicator on your dashboard that lights up when there's an issue with your vehicle's charging system, like a failing alternator or battery.
Can I drive with a P1108 code?
While the charging system itself might still be functional, the warning light circuit is not. This means you won't be alerted if the alternator fails, which could lead to being stranded. It's advisable to diagnose and repair it promptly.
Is P1108 related to the battery itself?
Not directly. P1108 indicates a problem with the circuit that tells you if there's a battery/charging issue, rather than a problem with the battery's charge level or health itself.
How do I know if the bulb is really the problem?
In many older vehicles, the battery light should illuminate briefly when you turn the ignition key to the 'On' position (before starting the engine) as a self-test. If it doesn't, the bulb or its circuit is likely at fault.
Will a P1108 code prevent my car from starting?
No, the code itself indicates a problem with the warning light circuit, not a direct failure of the starting or charging system. However, if an underlying charging issue goes unnoticed due to the faulty lamp circuit, it could eventually lead to a dead battery and a no-start condition.