P1108
BMWDual Alternator Battery Lamp Circuit Malfunction
Medium SeverityThis code indicates a fault in the warning light circuit connected to a dual alternator system, meaning the indicator lamp designed to alert the driver of charging system issues is not functioning correctly. While the primary charging system might still be operating, a malfunctioning warning light prevents the driver from being notified of potential problems with either alternator or the vehicle's electrical charging system.
⚠️ Before You Begin (Safety First)
Always disconnect the battery's negative terminal before performing any electrical work to prevent short circuits and electrical shock. Use proper insulated tools and avoid contact with live circuits. Ignoring a charging system warning could lead to a sudden loss of vehicle power.
Common Symptoms
- Check Engine Light (MIL) illumination
- Battery warning light on dashboard not illuminating when it should (e.g., with ignition on, engine off)
- Battery warning light illuminating intermittently or staying on
- Undercharging or overcharging conditions (if an actual charging fault exists concurrently)
- Dimming headlights or interior lights
- Difficulty starting the vehicle (if battery is drained due to unaddressed charging issue)
Common Causes
- Faulty wiring or connections in the battery lamp circuit for one or both alternators
- A defective instrument cluster (where the lamp is located)
- Issues with the voltage regulator or internal alternator fault preventing proper lamp signal
- A blown fuse affecting the lamp circuit
- Malfunctioning Engine Control Unit (ECU) or Body Control Module (BCM) affecting lamp control
Frequently reported on: General/Universal for BMWs with aftermarket or highly specialized dual alternator systems
Diagnostic Steps
- Visually inspect the wiring and connectors related to both alternators and the battery warning light circuit for any signs of damage, corrosion, or looseness.
- Check all relevant fuses in the vehicle's fuse boxes that are linked to the charging system and instrument cluster.
- Test the vehicle's battery voltage with the engine off and running to ensure proper charging output from both alternators (if accessible for individual testing).
- If the instrument cluster bulb or LED for the battery warning light is replaceable, check its functionality.
- Use an OBD-II scanner to clear the code and see if it returns, or to check for other related codes that might indicate an underlying charging issue.
👨🔧 When to Call a Professional
If the battery light on your dashboard is on, flickering, or not coming on at all when it should, and especially if you experience any other electrical issues or charging problems, it is crucial to have the vehicle inspected by a professional immediately to prevent a complete loss of power while driving.
Commonly Asked Questions
What does P1108 'Dual Alternator Battery Lamp Circuit Malfunction' mean?
It indicates that the dashboard warning light, which is designed to alert you about issues with your vehicle's dual alternator charging system, is not functioning correctly. This means you might not be warned if a problem with an alternator or the charging system occurs.
Can I drive with a P1108 code?
While your vehicle might still operate, it is not recommended to drive for an extended period with this code. The primary concern is that a malfunctioning warning light means you won't be notified if a serious charging issue develops, potentially leading to a dead battery and leaving you stranded.
Is P1108 a common code for BMWs?
This specific definition of P1108 related to a 'dual alternator' is very rare for most standard BMW passenger vehicles, as they typically come equipped with a single alternator. It is more likely to apply to highly specialized, customized, or modified BMWs that have a dual alternator setup.
What parts might be involved in fixing a P1108 code?
Potential parts involved include the alternator(s), the wiring harness and connectors for the charging system and instrument cluster, relevant fuses, the battery warning light bulb or LED within the instrument cluster, or possibly a fault within the vehicle's control modules (ECU/BCM).
How can I confirm if my BMW has a dual alternator system?
You should check your vehicle's owner's manual or consult a BMW service center for definitive information about your specific model's charging system. A visual inspection of the engine bay might also reveal a second alternator, though they can sometimes be concealed.