Dual Alternator Lower Circuit Malfunction (Control)
The P1107 code indicates a malfunction in the lower control circuit of a dual alternator system. This typically means the PCM has detected an abnormal voltage or signal from the secondary alternator's control circuit, often due to wiring issues, a faulty alternator, or a problem with the PCM itself. The dual alternator system is common in high-demand vehicles like ambulances, RVs, or police cruisers.
01. Most Common Causes
- Faulty secondary alternator
- Open or shorted wiring in the control circuit
- Corroded or loose connectors
- Failed PCM (less common)
02. Symptoms You Will Notice
- Battery warning light illuminated
- Low battery voltage or charging system warning
- Electrical accessories dimming or malfunctioning
- Engine stalling or hard starting
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the alternator wiring and connectors for damage or corrosion.
Step 3: Test the alternator output voltage at idle and under load.
Step 4: Check the control circuit continuity and resistance between the alternator and PCM.
Step 5: If wiring is good, test or replace the secondary alternator.
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 charging system may fail, leading to a dead battery and potential stalling.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Alternator replacement can range from $200-$600 depending on the vehicle and labor.