C1168

What Does Code C1168 Mean?

The diagnostic trouble code C1168 signifies a Rear Right (RR) Wheel Speed Sensor Coherency Fault. This code is typically set by the Anti-lock Brake System (ABS) control module, which often communicates with or is integrated into the Powertrain Control Module (PCM) via the Controller Area Network (CAN) bus. The ABS module continuously monitors the rotational speed of each wheel using dedicated wheel speed sensors. A “coherency fault” indicates that the signal received from the rear right wheel speed sensor is implausible, intermittent, or inconsistent when compared to other wheel speed sensor inputs, the vehicle speed sensor (VSS) reading, or other relevant vehicle operational data (e.g., engine RPM, transmission output speed, steering angle). It does not necessarily mean an open or short circuit, but rather a data integrity issue where the signal is present but not logical or reliable for proper system operation. When this condition is detected, the ABS module registers the fault, illuminates the ABS warning light, and may disable related systems such as Traction Control (TCS) and Electronic Stability Control (ESC/ESP) to prevent erroneous operation.

Common Symptoms

• ABS Warning Light Illumination: The Anti-lock Brake System warning indicator will illuminate on the instrument cluster.
• Traction Control System (TCS) Warning Light Illumination: The TCS indicator will likely be ON, indicating the system is disabled.
• Electronic Stability Control (ESC/ESP) Warning Light Illumination: The ESC/ESP indicator may also be ON, signaling system disablement.
• Erratic or Non-Functional ABS/TCS/ESC: These systems may activate inappropriately, fail to activate when needed, or be completely inoperative.
• Cruise Control Inoperation: The cruise control system often relies on accurate wheel speed data and may be disabled.
• Transmission Shifting Irregularities: In some vehicles, wheel speed data can influence transmission shift points, potentially leading to rough or incorrect gear changes.
• Speedometer/Odometer Inaccuracies: While less common for an individual wheel speed sensor, if the VSS relies on a calculated average or the affected sensor for its primary input, inaccuracies may occur.

What Causes the Code C1168?

• Faulty Rear Right Wheel Speed Sensor: Internal electronic failure, sensor head damage, or contamination affecting its ability to generate an accurate, consistent signal. This can include issues with passive (inductive) sensors failing to produce a sufficient AC voltage signal, or active (Hall-effect) sensors failing to produce a clear digital square wave.
• Damaged Wheel Speed Sensor Wiring Harness: Compromised integrity of the electrical circuit between the RR sensor and the ABS module, including frayed, cut, shorted, or open wiring. Connector issues such as corrosion, bent pins, or inadequate terminal tension at either the sensor or ABS module end are also common.
• Damaged or Contaminated ABS Tone Ring/Reluctor Wheel: The metallic ring with teeth or magnetic poles that the sensor reads can be cracked, bent, rusted excessively, missing teeth, or obscured by foreign debris (e.g., metallic particles, mud, road grime). This results in an inconsistent or absent signal to the sensor.
• Excessive Wheel Bearing Play: Looseness or wear in the rear right wheel bearing can cause the tone ring to wobble relative to the stationary sensor, leading to variations in the air gap and an erratic signal.
• ABS Control Module Internal Fault: Though less frequent for a single wheel coherency fault, an internal circuit board failure or software glitch within the ABS module specific to the RR sensor input could be the root cause.

How to Diagnose and Troubleshoot

Diagnosis of C1168 requires a methodical approach, utilizing an OBD-II scanner and a digital multimeter (DMM).

1. Retrieve and Document DTCs: Connect an OBD-II scanner capable of accessing ABS module data. Retrieve all stored Diagnostic Trouble Codes (DTCs), including historical and pending codes, and note them. This helps identify any related issues.
2. Visual Inspection:
   • Visually inspect the Rear Right wheel speed sensor and its entire wiring harness. Look for signs of physical damage, chafing, cuts, or rodent damage. Pay close attention to areas where the harness passes through suspension components or near moving parts.
   • Examine the sensor electrical connector for corrosion, bent or pushed-out pins, or poor seating. Disconnect, inspect, and reconnect securely.
   • Inspect the ABS tone ring (reluctor wheel). This component is typically located on the axle shaft, CV joint, or inside the wheel hub bearing assembly. Look for cracks, bent or missing teeth, excessive rust buildup, or accumulated foreign debris. Jack up the rear of the vehicle safely and rotate the wheel by hand to inspect the entire circumference of the tone ring.
   • Check for excessive wheel bearing play on the rear right wheel. With the vehicle safely lifted, grasp the wheel at the 12 and 6 o’clock positions, then the 3 and 9 o’clock positions, and attempt to rock it. Any noticeable play can affect sensor-to-tone-ring spacing.
3. Live Data Analysis (OBD-II Scanner):
   • Access the live data stream for all four wheel speed sensors within the ABS module.
   • With the vehicle safely lifted and supported, manually spin each wheel and observe the corresponding speed readings. All sensors should register a consistent, plausible speed. Pay particular attention to the RR sensor.
   • If possible, perform a road test on a smooth, straight road at a steady speed (e.g., 20-30 mph). Monitor all four wheel speed sensor readings simultaneously. The RR sensor reading should closely match the other wheel speeds. A coherency fault will likely manifest as erratic fluctuations, sudden drops to zero, or a consistently deviating reading from the other wheels.
4. Electrical Testing (Digital Multimeter – DMM):
   • Sensor Resistance Check (for passive/inductive sensors): Disconnect the RR wheel speed sensor connector. Using a DMM, measure the resistance across the sensor’s two signal terminals. Consult the vehicle manufacturer’s specifications, but a typical good inductive sensor will exhibit resistance between 800-2000 ohms. An open circuit (OL on DMM) or very low resistance (near 0 ohms) indicates an internal sensor fault. (Note: This test is not applicable to active/Hall-effect sensors, which require power to operate and generate a digital signal).
   • Voltage/Frequency Testing (for active/Hall-effect sensors): These sensors typically have three wires: power, ground, and signal. With the sensor connected and ignition ON (or engine running, per service manual), back-probe the sensor connector. Check for the specified supply voltage (usually 5V or 12V) and a good ground. Then, with the wheel spinning, monitor the signal wire. An oscilloscope is ideal for visualizing the square wave signal, but a DMM in AC voltage or frequency mode might show a fluctuating reading, indicating activity.
   • Wiring Continuity and Integrity Check: Disconnect both ends of the RR wheel speed sensor harness (at the sensor and at the ABS module). Use the DMM to check for continuity on each wire from end-to-end (should read very low resistance, typically < 0.5 ohms). Then, check each wire for shorts to ground (should read Open Line - OL) and shorts to power (should also read OL). Test for inter-wire shorts as well.
5. Component Swap (if applicable): If all electrical tests are inconclusive but strong suspicion points to the sensor, and a known good, compatible RR wheel speed sensor is available, temporarily swap it and clear the code to see if the issue resolves.

Recommended Repairs and Solutions

Once the root cause of C1168 has been accurately identified through diagnosis, the appropriate repair can be undertaken:

• Replace the Rear Right Wheel Speed Sensor: This is the most frequent repair for C1168. Ensure the replacement sensor is a high-quality OEM part or a reputable aftermarket equivalent. During installation, verify proper seating and air gap (if adjustable) according to manufacturer specifications. Apply a thin coat of dielectric grease to the electrical connector terminals to prevent corrosion.
• Repair or Replace Wiring Harness and Connectors: If damaged wiring or corroded/faulty connectors are identified, repair them using proper wiring repair techniques (e.g., soldering and heat-shrink tubing for splices) or replace the entire harness section if the damage is extensive. Ensure all connections are watertight and secure.
• Clean or Replace ABS Tone Ring: If the tone ring is merely contaminated with debris or rust, carefully clean it using a non-residue brake cleaner and a wire brush (if safe for the material). If the tone ring is cracked, bent, severely corroded, or has missing teeth, it must be replaced. This often necessitates replacing the wheel hub assembly or axle shaft, depending on how the tone ring is integrated.
• Replace Wheel Bearing: If excessive wheel bearing play is confirmed as the cause, the entire wheel bearing assembly on the rear right must be replaced to restore proper sensor-to-tone-ring spacing and operation.
• ABS Module Replacement: This is a significantly more expensive repair and should only be considered after all other possibilities have been thoroughly exhausted and confirmed. ABS module replacement often requires programming or calibration with a manufacturer-specific scan tool after installation.

After any repair, always clear the DTCs using an OBD-II scanner and perform a comprehensive road test to confirm the fix and ensure that C1168, and any related ABS/TCS/ESC warning lights, do not return. Always consult the vehicle-specific service manual for detailed component locations, wiring diagrams, and testing procedures.