What Does B1557 Mean?
This code indicates the Body Control Module (BCM) or related control module has detected an unwanted voltage on the ignition run/start circuit that exceeds normal system voltage, suggesting a short to battery power. This circuit controls power distribution to vehicle systems during run and start positions of the ignition switch. The fault means an electrical path exists where battery voltage is being applied to the circuit when it shouldn't be, potentially causing unintended system activation or preventing proper ignition control.
Common Causes
40%
Damaged or chafed wiring harness causing direct short to battery voltage in ignition switch circuit or BCM connector area
30%
Faulty ignition switch with internal short circuit allowing constant battery voltage feed
20%
Defective Body Control Module with internal circuit failure on ignition control output
10%
Corroded or damaged connector pins at BCM or ignition switch causing cross-circuit contamination
Diagnostic Steps
1
Step 1: Perform visual inspection of ignition switch wiring harness from switch to BCM, looking for chafed insulation, melted wires, or damage near sharp edges and mounting brackets. Check all related connectors for corrosion, pushed-out pins, or signs of overheating.
2
Step 2: With ignition OFF and key removed, disconnect BCM connector. Using a digital multimeter, measure voltage on the ignition run/start circuit terminal at the BCM harness side. Reading should be 0V with key off; if battery voltage (12V+) is present, the short is between BCM and ignition switch.
3
Step 3: If voltage found in Step 2, disconnect ignition switch connector and retest at BCM harness. If voltage disappears, ignition switch is faulty. If voltage persists, harness has short to power between these points - inspect and trace wire routing carefully.
4
Step 4: If no voltage found at BCM harness in Step 2, reconnect BCM and monitor circuit voltage with ignition in various positions (OFF, ACC, RUN, START) using bi-directional scan tool controls if available. Unexpected battery voltage in wrong key positions confirms faulty BCM.
5
Step 5: After identifying and repairing fault (replace switch, repair harness, or replace BCM), clear codes, cycle ignition through all positions multiple times, and verify code does not return. Test all accessory and starting functions for proper operation.
Estimated Repair Cost
$150 - $800
Parts + labor, varies by vehicle and location
This code indicates the Body Control Module (BCM) or related control module has detected an unwanted voltage on the ignition run/start circuit that exceeds normal system voltage, suggesting a short to battery power. This circuit controls power distribution to vehicle systems during run and start pos...
The most common cause of B1557 (Ignition Run/Start Circuit Short To Battery) is: Damaged or chafed wiring harness causing direct short to battery voltage in ignition switch circuit or BCM connector area
Typical repair costs for B1557 range from $150 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may be drivable but could experience unintended accessory activation, no-start conditions, or battery drain issues. Repair within 1-2 days as electrical shorts pose fire risk and can cause further electrical system damage or leave you stranded.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1557 to identify the root cause.
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Quick Info
Category
Body
System
Body Electrical System / Ignition Control
Difficulty
Type
Manufacturer
Recommended Tools
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