What Does B1580 Mean?
This code indicates the Body Control Module (BCM) has detected an open circuit in the dashboard dimmer switch increase input signal wire. The dimmer control system, which allows the driver to adjust instrument panel and interior lighting brightness, has lost communication or signal from the brightness increase button or switch. This prevents the driver from increasing the illumination level of the dashboard and interior lights.
Common Causes
35%
Open circuit or broken wire in the dimmer switch increase signal wire between switch and BCM
30%
Failed or damaged dimmer switch assembly with internal open circuit on increase function
20%
Corroded or loose connector at dimmer switch or BCM causing intermittent or permanent open circuit
10%
Failed Body Control Module with internal circuit fault on dimmer increase input channel
5%
Blown fuse or open circuit in dimmer switch power supply affecting switch operation
Diagnostic Steps
1
Step 1: Perform visual inspection of the dashboard dimmer switch assembly and surrounding trim for physical damage, loose mounting, or obvious wiring issues. Check all accessible connectors for corrosion, bent pins, or loose connections.
2
Step 2: Using a digital multimeter, backprobe the dimmer switch connector at the increase input terminal while pressing the increase button. Verify voltage changes from open circuit (typically 5V or 12V reference) to ground when button is activated.
3
Step 3: If no signal change occurs at switch connector, remove dimmer switch assembly and test continuity through the increase circuit internally with multimeter in ohms mode while activating the button. Should read near 0 ohms when pressed, infinite when released.
4
Step 4: If switch tests good, trace wiring from dimmer switch connector to BCM connector checking for continuity, shorts to ground, or shorts to power along entire circuit length. Pay special attention to harness routing through door jambs or under dashboard where wiring may flex and break.
5
Step 5: At BCM connector, verify proper terminal tension and absence of corrosion on the dimmer increase input pin. Check BCM ground circuits for integrity with multimeter resistance test (should be less than 0.5 ohms to chassis ground).
6
Step 6: After repairs, clear codes and verify dimmer increase function operates correctly through full range. Monitor for code recurrence during test drive with multiple dimmer switch activations.
Estimated Repair Cost
$75 - $350
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected an open circuit in the dashboard dimmer switch increase input signal wire. The dimmer control system, which allows the driver to adjust instrument panel and interior lighting brightness, has lost communication or signal from the brightne...
The most common cause of B1580 (Dim Panel Increase Input Circuit Open) is: Open circuit or broken wire in the dimmer switch increase signal wire between switch and BCM
Typical repair costs for B1580 range from $75 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving as this only affects interior lighting brightness adjustment capability and does not impact vehicle operation or safety systems. Repair at convenience, though excessively bright or dim dashboard 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 B1580 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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