What Does B1579 Mean?
This code indicates the Body Control Module (BCM) has detected a circuit malfunction in the dimmer panel increase input signal. This system controls the dashboard and interior lighting brightness adjustment when the driver presses the 'increase' or 'up' button on the dimmer switch. The BCM has identified either an open circuit, short circuit, or abnormal voltage in the circuit that should carry the brightness increase command signal.
Common Causes
45%
Faulty dimmer switch or stuck/corroded increase button contact
30%
Broken, chafed, or corroded wiring between dimmer switch and BCM
15%
Poor connection or corrosion at dimmer switch connector or BCM connector
10%
Failed Body Control Module internal circuit or input channel
Diagnostic Steps
1
Step 1: Locate the dimmer switch assembly (typically on dashboard left of steering wheel or integrated into headlight switch) and visually inspect for physical damage, broken buttons, or signs of liquid intrusion
2
Step 2: Using a digital multimeter, backprobe the dimmer increase input signal wire at the BCM connector while operating the dimmer increase button - verify voltage changes from ground to 5V or 12V (manufacturer dependent) when button is pressed
3
Step 3: If no voltage change detected, disconnect dimmer switch connector and check for continuity between the increase signal terminal and the corresponding BCM pin using wiring diagram - should show less than 5 ohms resistance with button pressed
4
Step 4: Inspect both the dimmer switch connector and BCM connector for bent pins, corrosion, or moisture - clean with electrical contact cleaner and apply dielectric grease if corrosion found
5
Step 5: If wiring and connections test good, test the dimmer switch by measuring resistance across increase button terminals while pressing button - should show continuity when pressed and open circuit when released
6
Step 6: If all previous tests pass, substitute a known-good dimmer switch or perform BCM input voltage test per manufacturer specifications - if BCM does not recognize valid input signals, BCM replacement may be required
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a circuit malfunction in the dimmer panel increase input signal. This system controls the dashboard and interior lighting brightness adjustment when the driver presses the 'increase' or 'up' button on the dimmer switch. The BCM has ident...
The most common cause of B1579 (Dim Panel Increase Input Circuit Failure) is: Faulty dimmer switch or stuck/corroded increase button contact
Typical repair costs for B1579 range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as this only affects the ability to increase dashboard brightness and does not impact vehicle operation or safety systems. Repair at convenience, though reduced ability to adjust dash lighting may cause eye strain during night driving.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1579 to identify the root cause.
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Quick Info
Category
Body
System
Interior Lighting Control System
Difficulty
Type
Manufacturer
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