Dual Alternator Lower Fault (Control)
The P1106 code indicates a fault in the lower alternator control circuit of a dual alternator system. This typically means the powertrain control module (PCM) has detected an abnormal voltage or signal from the lower alternator's control wire, often due to wiring issues, a faulty alternator, or a problem with the PCM itself. The dual alternator system is common in heavy-duty trucks and commercial vehicles to provide extra electrical capacity.
01. Most Common Causes
- Faulty lower alternator
- Damaged or corroded wiring/connectors in the control circuit
- Blown fuse or fusible link
- Faulty PCM or voltage regulator
02. Symptoms You Will Notice
- Battery warning light illuminated
- Low battery voltage or dead battery
- Electrical system issues (dim lights, weak accessories)
- Engine stalling or hard starting
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and check freeze frame data.
Step 2: Inspect wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the lower alternator output voltage and control signal with a multimeter.
Step 4: Check fuses and fusible links related to the alternator circuit.
Step 5: If wiring and fuses are good, test or replace the lower alternator.
Step 6: If problem persists, diagnose PCM or voltage regulator.
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 discharge, leading to a stall or inability to restart. Limited driving to a repair shop is acceptable if the battery is fully charged.
How much does it cost to fix?▼
The cost typically ranges from $150 to $400, including parts and labor. Alternator replacement is the most common fix, costing $100-$300 for the part and $50-$100 for labor.