OBD-II Fault Code

P1108: Dual Alternator Battery Lamp Circuit Malfunction

Meaning, symptoms, likely causes, diagnostic checks and repair guidance for P1108.

System family

Powertrain

Manufacturer-specific

Repair category

Lighting

Use this category to narrow your checks before replacing parts.

Severity

Medium

Severity is a general guide. Confirm with scan-tool data and vehicle symptoms.

What P1108 usually means

Dual Alternator Battery Lamp Circuit Malfunction.

Common symptoms

Check Engine light; Poor drivability or reduced fuel economy depending on fault

Likely causes

Blown bulb/LED module; Poor ground; Fuse/relay fault; Switch/module/wiring issue

Diagnostic checks

Scan all modules and record freeze-frame data before clearing codes; Check battery voltage and related fuses; Check bulb/module, fuse, ground and connector corrosion

Repair guidance

Replace failed bulb/module, repair ground/wiring, replace switch/relay if confirmed

Verification after repair

Clear code, road-test through the same drive condition, then rescan

Note: Confirm vehicle make/model/year because manufacturer-specific codes can vary; Manufacturer-specific: confirm definition and test steps in the vehicle service manual. A DTC identifies a circuit or system condition, not always the failed part.