C1178 – OBD-II DTC

OBD-II DTC C1178 – Speed Wheel Sensor LR Coherency Fault

DTC C1178 meaning

DTC C1178 refers to a “Speed Wheel Sensor LR Coherency Fault.” This diagnostic trouble code indicates that the left rear speed wheel sensor is providing inconsistent or erroneous data compared to the other wheel speed sensors. The vehicle’s onboard diagnostic system monitors the speed of each wheel to ensure proper operation of the anti-lock braking system (ABS) and traction control systems. When a discrepancy is detected, the system triggers this fault code.

DTC C1178 symptoms

Common symptoms associated with DTC C1178 may include:

• Illumination of the ABS warning light on the dashboard
• Inconsistent or erratic ABS operation
• Loss of traction control functionality
• Unusual braking behavior, such as locking up or skidding
• Potential activation of the traction control warning light

DTC C1178 causes

Several factors can lead to the triggering of DTC C1178, including:

• Faulty left rear wheel speed sensor
• Damaged wiring or connectors related to the wheel speed sensor
• Corrosion or dirt buildup on the sensor or its mounting surface
• Issues with the ABS control module
• Faulty wheel bearings affecting sensor readings

DTC C1178 seriousness

DTC C1178 is considered a serious issue as it affects the vehicle’s braking and stability control systems. If left unaddressed, it can lead to:

• Increased risk of accidents due to compromised braking performance
• Potential for further damage to the ABS system
• Inability to effectively control the vehicle in slippery conditions

How to diagnose DTC C1178

To diagnose DTC C1178, follow these steps:

1. Use an OBD-II scanner to confirm the presence of the C1178 code.
2. Inspect the left rear wheel speed sensor and its wiring for visible damage or disconnections.
3. Check the sensor’s resistance and voltage output using a multimeter.
4. Compare the readings from the left rear sensor with those from the other wheel speed sensors.
5. Examine the ABS control module for any additional fault codes or issues.

How to fix DTC C1178 step-by-step instructions

To fix DTC C1178, follow these steps:

1. Inspect and clean the left rear wheel speed sensor and its mounting area.
2. Repair or replace any damaged wiring or connectors associated with the sensor.
3. Test the left rear wheel speed sensor for proper operation and replace it if necessary.
4. Clear any fault codes from the vehicle’s computer using an OBD-II scanner.
5. Perform a road test to ensure that the ABS and traction control systems are functioning correctly.

How to erase DTC C1178

To erase DTC C1178, follow these steps:

1. Connect an OBD-II scanner to the vehicle’s diagnostic port.
2. Turn on the ignition without starting the engine.
3. Navigate to the “Erase Codes” or “Clear Codes” option on the scanner.
4. Confirm the action to clear the DTCs from the vehicle’s memory.
5. Disconnect the scanner and start the vehicle to verify that the code does not reappear.

Recommended tools for OBD-II diagnostics

Explore our expert picks: The Best OBD2 Scanners for 2025

Easy-to-use Multimeter for reliable diagnostics: AstroAI Auto-ranging Multimeter

Some of the links on this page may be affiliate links, which means we may earn a small commission if you make a purchase. This helps us keep our DTC database up to date and provide valuable content for free. We only recommend products that we have tested and believe to be the best in their class.