What Does C1256 Mean?
The ABS control module has detected a short to battery voltage on the right rear ABS inlet valve coil circuit. The module is reading unwanted high voltage on this valve driver line, potentially causing the valve to remain energized and continuously block brake pressure application to the right rear wheel.
Safety Warning
A constantly energized inlet valve could block brake fluid to the right rear wheel, severely reducing braking force at that corner. This is a critical safety concern requiring immediate attention.
Common Causes
30%
Shorted valve driver transistor or power FET inside the ABS module providing constant voltage to the coil
30%
Internal wiring short to a power feed inside the ABS module housing
25%
Valve coil insulation failure with contact to an internal power conductor in the modulator
15%
Contamination or moisture bridging a powered circuit to the valve coil trace on the module board
Diagnostic Steps
1
Step 1: Disconnect the ABS module from the hydraulic unit. With key on, measure voltage on each inlet valve coil wire at the module connector. No voltage should appear without a commanded test.
2
Step 2: With key off and everything disconnected, measure resistance from each valve wire to battery positive to identify the short location.
3
Step 3: Examine the ABS module circuit board for damaged valve driver components — look for burnt, discolored, or swollen transistors/FETs.
4
Step 4: Measure valve coil insulation resistance from each terminal to any power-carrying conductor in the modulator.
5
Step 5: Replace the faulted component. Clear codes and verify all inlet and outlet valves operate correctly via bidirectional scan tool commands.
Estimated Repair Cost
$300 - $1,200
Parts + labor, varies by vehicle and location
The ABS control module has detected a short to battery voltage on the right rear ABS inlet valve coil circuit. The module is reading unwanted high voltage on this valve driver line, potentially causing the valve to remain energized and continuously block brake pressure application to the right rear ...
The most common cause of C1256 (ABS Inlet Valve Coil RR Circuit Short To Battery) is: Shorted valve driver transistor or power FET inside the ABS module providing constant voltage to the coil
Typical repair costs for C1256 range from $300 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A constantly energized inlet valve could block brake fluid to the right rear wheel, severely reducing braking force at that corner. This is a critical safety concern requiring immediate attention.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to C1256 to identify the root cause.
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Quick Info
Category
Chassis
System
Anti-lock Brake System (ABS)
Difficulty
Type
Manufacturer
Recommended Tools
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