What Does B1577 Mean?
This code indicates the Body Control Module (BCM) has detected a short to battery voltage on the park lamp input circuit. The BCM monitors the park lamp switch input signal and expects a specific voltage range; when it detects continuous battery voltage (12V+) on this circuit when it should be at a lower reference voltage or ground, it sets this fault. This typically affects the parking lamp system, preventing proper control of exterior parking/marker lights.
Common Causes
40%
Damaged or chafed wiring harness causing direct short to power between park lamp switch and BCM
30%
Faulty park lamp switch with internal short to power supply
20%
Corroded or moisture-damaged connector pins creating unintended voltage path at BCM or switch connector
10%
Failed Body Control Module with internal circuit fault on park lamp input
Diagnostic Steps
1
Step 1: Perform visual inspection of park lamp switch and all accessible wiring from switch to BCM for obvious damage, chafing against metal, melted insulation, or aftermarket wiring installations that may contact power circuits
2
Step 2: Disconnect park lamp switch connector and measure voltage at the BCM-side harness terminal with ignition on using a digital multimeter; reading should be 0-0.5V (pull-down circuit) or 5V (reference voltage), not battery voltage (12V+)
3
Step 3: If battery voltage is present at disconnected harness, trace wiring between switch and BCM checking for pinch points, harness routing near power distribution, and connector pin-to-pin shorts; perform continuity test between park lamp circuit and known power circuits
4
Step 4: If no voltage present at disconnected harness, reconnect switch and measure input voltage at BCM connector while manually operating park lamp switch positions; if battery voltage appears in all positions, replace park lamp switch
5
Step 5: Clear codes, cycle ignition and park lamp switch through all positions, and verify code does not return; monitor live data for park lamp input status during testing to confirm proper signal levels
Estimated Repair Cost
$75 - $450
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) has detected a short to battery voltage on the park lamp input circuit. The BCM monitors the park lamp switch input signal and expects a specific voltage range; when it detects continuous battery voltage (12V+) on this circuit when it should be at a ...
The most common cause of B1577 (Lamp Park Input Circuit Short To Battery) is: Damaged or chafed wiring harness causing direct short to power between park lamp switch and BCM
Typical repair costs for B1577 range from $75 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive during daylight hours, but parking lamps may not function properly which reduces visibility to other drivers at night or in low-light conditions. Repair within a few days to maintain proper lighting safety compliance.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1577 to identify the root cause.
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Quick Info
Category
Body
System
Exterior Lighting System
Difficulty
Type
Manufacturer
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