What Does C1187 Mean?
The brake fluid level sensor input circuit is open. The ABS module cannot read the brake fluid level in the master cylinder reservoir because the sensor's signal wire is broken or disconnected. This is a safety-critical circuit — if the module cannot verify adequate fluid level, it will disable ABS as a precaution. The brake warning light and ABS light will both illuminate.
Safety Warning
If the fluid level is actually low, the brakes may be compromised — do NOT drive until the cause is identified (worn pads, leak, etc.). If the sensor circuit is simply open and fluid level is normal, ABS is disabled as a precaution but conventional brakes work. Still, have it repaired immediately as you have no fluid level monitoring.
Common Causes
30%
Brake fluid level sensor connector disconnected or corroded
30%
Failed brake fluid level sensor (internal open circuit)
25%
Broken wire between the sensor and the ABS/instrument cluster module
15%
Actually low brake fluid level causing the sensor float to drop below the contact threshold
Diagnostic Steps
1
First, visually check the brake fluid level in the reservoir. If it is below the MIN line, top off with the correct DOT specification fluid and inspect the entire brake system for leaks. Low fluid is a symptom of worn brake pads or a leak — do not just top off and ignore.
2
If fluid level is adequate, locate the brake fluid level sensor on the reservoir. Disconnect and reconnect the sensor connector firmly. Check for corrosion or brake fluid contamination on the pins.
3
With the sensor connector disconnected, measure the sensor resistance. Most float-type sensors read near 0 ohms when fluid is at the proper level (float up, switch closed) and OL when low. If it reads OL with adequate fluid, replace the sensor.
4
Check continuity from the sensor harness connector to the ABS module connector pins. An OL reading indicates an open in the wiring harness.
5
If the sensor and wiring are good, bridge the sensor connector pins with a jumper wire. If the warning lights clear and the ABS code does not return, confirm the sensor is the issue.
Estimated Repair Cost
$15 - $200
Parts + labor, varies by vehicle and location
The brake fluid level sensor input circuit is open. The ABS module cannot read the brake fluid level in the master cylinder reservoir because the sensor's signal wire is broken or disconnected. This is a safety-critical circuit — if the module cannot verify adequate fluid level, it will disable ABS ...
The most common cause of C1187 (Brake Fluid Level Sensor Input Open Circuit) is: Brake fluid level sensor connector disconnected or corroded
Typical repair costs for C1187 range from $15 to $200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
If the fluid level is actually low, the brakes may be compromised — do NOT drive until the cause is identified (worn pads, leak, etc.). If the sensor circuit is simply open and fluid level is normal, ABS is disabled as a precaution but conventional brakes work. Still, have it repaired immediately as you have no fluid level monitoring.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to C1187 to identify the root cause.
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Quick Info
Category
Chassis
System
ABS / Brake Hydraulic System
Difficulty
Type
Manufacturer
Recommended Tools
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