Dual Alternator Battery Lamp Circuit Malfunction
The P1108 code indicates a malfunction in the battery lamp circuit of a dual alternator system. This typically occurs when the powertrain control module (PCM) detects an incorrect voltage signal from the alternator's battery lamp circuit, often due to a faulty alternator, wiring issues, or a defective voltage regulator. The dual alternator system is common in heavy-duty trucks and high-output vehicles, and this code can lead to charging system failures if not addressed.
01. Most Common Causes
- Faulty alternator (primary or secondary)
- Damaged wiring or connectors in the battery lamp circuit
- Defective voltage regulator
- Blown fuse or fusible link
- PCM software or hardware issue
02. Symptoms You Will Notice
- Battery warning light illuminated on the dashboard
- Battery not charging or undercharging
- Dimming headlights or electrical issues
- Engine stalling or difficulty starting
- Possible battery drain
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and verify P1108 is present.
Step 2: Visually inspect the alternator wiring and connectors for damage or corrosion.
Step 3: Test the battery voltage with the engine running; should be 13.5-14.5 volts.
Step 4: Check the battery lamp circuit for continuity and proper voltage using a multimeter.
Step 5: If wiring is intact, test the alternator output and voltage regulator; replace if faulty.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the battery may not charge properly, leading to a dead battery or stalling. Seek repair soon.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnostic and minor repairs, but alternator replacement can cost $200-$500 or more.