OBD-II Fault Code

P1105: Dual Alternator Upper Fault

Meaning, symptoms, likely causes, diagnostic checks and repair guidance for P1105.

System family

Powertrain

Manufacturer-specific

Repair category

Power supply / charging

Use this category to narrow your checks before replacing parts.

Severity

High

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

What P1105 usually means

Dual Alternator Upper Fault.

Common symptoms

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

Likely causes

Weak battery; Charging system fault; Loose/corroded terminals; Poor ground

Diagnostic checks

Scan all modules and record freeze-frame data before clearing codes; Check battery voltage and related fuses; Test battery state of charge and charging voltage; Inspect terminals and ground straps

Repair guidance

Clean/tighten terminals, replace weak battery, repair alternator/charging circuit as needed

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.