C1187
Brake Fluid Level Sensor Input Open Circuit
Chassis Chassis/Safety Brake fluid monitoring 🔴 Serious — Stop or limit driving
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What This Actually Means
In plain language — no jargon

The brake fluid level sensor wire is broken or disconnected, so the brake control module can't detect how much fluid is in the reservoir. It's like a fuel gauge with a broken wire—the system has no way to read the actual level.

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Symptoms You May Notice
3 known symptoms for this code
ABS warning light illuminated on dashboard
Brake system warning light activated
Loss of ABS functionality
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the voltage signal from the brake fluid level sensor, which should vary between 0.5V and 4.5V depending on fluid level. An open circuit means no signal is received, causing the voltage to drop to 0V or become unstable. The module interprets this as a sensor malfunction and triggers the fault code.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Sensor voltage signal 0.5V to 4.5V proportional to fluid level 0V or no signal detected (open circuit)
Signal continuity Continuous signal present Intermittent or absent signal
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Brake fluid level sensor connector
Inspect and reseat the connector at the brake fluid reservoir to ensure proper contact.
2
Sensor wiring harness
Check the wire harness from the sensor to the ABS module for damage, corrosion, or disconnection and repair as needed.
3
Brake fluid level sensor
Replace the sensor if wiring and connectors are intact but signal remains absent.