What Does B1595 Mean?
This code indicates that the Body Control Module (BCM) has detected an invalid or out-of-range signal from the ignition switch position sensor or circuit. The BCM monitors the ignition switch for proper voltage signals corresponding to different key positions (OFF, ACC, RUN, START), and has identified a signal that does not match any expected value or an illegal combination of signals. This is a manufacturer-specific body code that affects the vehicle's starting and accessory power systems.
Safety Warning
This is a critical safety issue that may prevent vehicle starting, cause unexpected stalling, or disable safety systems. The vehicle may become inoperable or experience intermittent loss of power steering and braking assist. Repair immediately and avoid driving until resolved.
Common Causes
45%
Faulty ignition switch assembly with worn contacts or internal failure sending incorrect position signals
30%
Damaged or corroded wiring harness, connectors, or terminals between ignition switch and BCM
15%
Faulty ignition lock cylinder mechanism causing misalignment or incomplete switch engagement
10%
Body Control Module internal fault or software corruption causing misinterpretation of valid signals
Diagnostic Steps
1
Step 1: Perform a visual inspection of the ignition switch connector and wiring harness for physical damage, corrosion, pushed-out pins, or burnt terminals. Check for proper connector engagement and security.
2
Step 2: Using a digital multimeter, backprobe the ignition switch connector and measure voltage at each position terminal while cycling the key through OFF, ACC, RUN, and START positions. Compare readings to manufacturer specifications (typically 0V, 5V, or 12V depending on position and vehicle architecture).
3
Step 3: Check for intermittent connections by wiggling the wiring harness and ignition switch while monitoring live data with the scan tool for unexpected position changes or signal dropouts.
4
Step 4: If wiring and connections test normal, remove and bench-test the ignition switch assembly using a multimeter to verify proper continuity and resistance values across all switch positions per manufacturer specifications.
5
Step 5: Inspect the ignition lock cylinder for wear, binding, or incomplete key insertion that may prevent proper switch engagement. Verify the cylinder fully rotates through all positions.
6
Step 6: If all components test normal, perform BCM voltage supply and ground circuit tests. Clear codes, road test, and monitor for code recurrence. If code returns with verified good switch and wiring, consider BCM replacement or reprogramming.
Estimated Repair Cost
$150 - $650
Parts + labor, varies by vehicle and location
This code indicates that the Body Control Module (BCM) has detected an invalid or out-of-range signal from the ignition switch position sensor or circuit. The BCM monitors the ignition switch for proper voltage signals corresponding to different key positions (OFF, ACC, RUN, START), and has identifi...
The most common cause of B1595 (Ignition Switch Illegal Input Code) is: Faulty ignition switch assembly with worn contacts or internal failure sending incorrect position signals
Typical repair costs for B1595 range from $150 to $650, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This is a critical safety issue that may prevent vehicle starting, cause unexpected stalling, or disable safety systems. The vehicle may become inoperable or experience intermittent loss of power steering and braking assist. Repair immediately and avoid driving until resolved.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1595 to identify the root cause.
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Quick Info
Category
Body
System
Body Control and Ignition System
Difficulty
Type
Manufacturer
Recommended Tools
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