B1579: Dim Panel Increase Input Circuit Fault
The B1579 code indicates a fault in the dim panel increase input circuit, which carries the signal that tells the body control module (BCM) or interior lighting module to brighten the instrument panel and other interior lights. This circuit typically uses a pulse-width modulation (PWM) or analog signal from the dimmer switch. When the module detects an open, short, or abnormal resistance in the circuit, it logs this diagnostic trouble code.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty or worn dimmer switch/potentiometer
- Open circuit, short to ground, or short to voltage in the increase input wire
- Corroded, loose, or damaged connectors or pins
- Faulty body control module (BCM) or interior lighting module
- Abnormal resistance due to damaged wiring or poor splices
3. Symptoms You Will Notice
- Instrument panel lights stuck at a fixed brightness or unable to increase
- Interior lights (e.g., radio, climate control) not responding to dimmer adjustment
4. Step-by-Step Diagnosis
Scan for B1579 and check related module data for dimmer input signal
Visually inspect dimmer switch and wiring for damage or corrosion
Test dimmer switch resistance or voltage output per manufacturer specs
Check for open/short in the circuit between switch and BCM
If wiring and switch are good, suspect BCM or lighting module failure
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, the vehicle is safe to drive. This is a low-severity issue affecting only interior lighting adjustment.
How much does it cost to fix?▼
Repair costs typically range from $50 to $200 for a switch replacement, up to $500+ if the BCM needs replacement.