C1701

What Does Code C1701 Mean?

Diagnostic Trouble Code C1701 indicates a circuit fault within the Left Rear Wheel Speed Sensor (WSS) system, as detected by the Anti-lock Braking System (ABS) control module, or a combined Vehicle Stability Control (VSC)/Traction Control System (TCS) module. This code signifies that the control module is not receiving the expected electrical signal from the left rear wheel speed sensor, or the signal it receives is outside of the pre-programmed operational parameters. The module continuously monitors the resistance, voltage, and frequency/pattern of the signal generated by each WSS to calculate individual wheel rotational speed. A “circuit fault” implies an electrical anomaly such as an open circuit (no signal), a short circuit (signal pegged high or low), or an out-of-range resistance value preventing accurate data transmission. Consequently, the ABS, Traction Control, and Electronic Stability Control subsystems are compromised or rendered inoperative, as they rely critically on precise wheel speed data for their core functions.

Common Symptoms

• Illumination of the ABS Warning Light: The primary indicator that the Anti-lock Braking System has detected a fault.
• Illumination of the Traction Control (TCS) or Vehicle Stability Control (VSC/ESC) Warning Light: These systems share wheel speed data with the ABS and will often illuminate simultaneously.
• Loss of ABS Functionality: During hard braking, the wheels may lock up, indicating the ABS is not modulating brake pressure effectively.
• Degraded or Inoperative Traction Control: The vehicle may experience increased wheel spin during acceleration, especially on slippery surfaces.
• Compromised Stability Control Performance: The vehicle’s ability to correct oversteer or understeer during dynamic maneuvers may be reduced.
• Intermittent Harsh Braking or False ABS Activation: In rare cases, if the sensor provides an erratic or intermittent signal, the ABS system might misinterpret inputs and engage prematurely or harshly.

What Causes the Code C1701?

• Faulty Left Rear Wheel Speed Sensor: The sensor itself may have failed internally due to wear, exposure to elements, physical impact, or manufacturing defects, leading to an open circuit, short circuit, or inability to generate a coherent signal.
• Damaged Wiring Harness: The electrical wiring connecting the left rear WSS to the ABS control module can become chafed, cut, corroded, or develop an internal open or short circuit, particularly where it routes near moving suspension components or through wheel wells.
• Corroded Electrical Connector: Moisture, road salt, and debris can ingress into the multi-pin connector for the left rear WSS, causing corrosion on the terminals. This significantly increases electrical resistance or creates an open circuit, disrupting signal integrity.
• Damaged or Contaminated ABS Tone Ring: While technically a mechanical issue, severe damage (cracks, bent teeth, missing teeth) or excessive contamination (heavy rust, debris) on the tone ring (also known as a reluctor ring or exciter ring) can prevent the WSS from generating a consistent and accurate signal, which the ABS module may interpret as an electrical circuit fault.
• Faulty ABS Control Module: Although less common, an internal failure within the ABS control module itself can prevent it from correctly processing or receiving the signal from the left rear WSS, leading to the C1701 code. This is typically a last resort diagnosis.

How to Diagnose and Troubleshoot

A systematic diagnostic approach is crucial for accurately resolving C1701:

1. Perform a Thorough Visual Inspection: Begin by visually inspecting the left rear wheel speed sensor, its mounting, and the entire wiring harness leading from the sensor to the main body harness. Look for obvious signs of physical damage, chafing, cuts, stretched wires, or corrosion at the sensor and harness connectors. Pay particular attention to areas where the wiring passes through wheel wells or near suspension and exhaust components. Also, inspect the ABS tone ring through the wheel or by removing the wheel for any visible damage, cracks, or excessive accumulation of debris or rust.
2. Scan for All Relevant Codes and Live Data: Use an advanced OBD-II scanner capable of communicating with the ABS/VSC/TCS module. Confirm the presence of C1701 and check for any additional related codes that might indicate a broader system issue. Access the live data stream for all four wheel speed sensors. Drive the vehicle slowly (e.g., 5-15 mph) on a level surface while monitoring the wheel speed readings. The left rear sensor reading will likely be 0 MPH or display erratic, implausible values compared to the other three sensors if C1701 is active.
3. Test Sensor Resistance (for Passive Sensors): Disconnect the electrical connector at the left rear WSS. Using a Digital Multimeter (DMM) set to the ohms (Ω) scale, measure the resistance across the two terminals of the sensor itself. Consult the vehicle’s factory service manual for the specified resistance range (typically 1kΩ to 3kΩ for inductive/passive sensors). An “open loop” (OL) or infinite resistance, or a resistance value near 0Ω (short circuit), indicates an internal sensor fault. Active (Hall-effect or magnetoresistive) sensors cannot be tested this way, as they require power to operate.
4. Test Wiring Harness for Continuity and Shorts: With the left rear WSS disconnected and the ABS control module connector disconnected (if accessible), use the DMM to check for continuity between the corresponding terminals at the WSS connector and the ABS module connector. A reading of “OL” or high resistance indicates an open circuit in the wire. Next, check for shorts to ground by placing one DMM lead on each wire terminal and the other lead on a known good chassis ground. Then, check for shorts to power by checking for continuity between wires in the harness. Any continuity to ground or power, or between two wires, indicates a wiring fault.
5. Test Sensor Signal (for Active Sensors): For vehicles equipped with active wheel speed sensors, a DMM may not provide sufficient diagnostic information. These sensors typically require a 5V or 12V power supply. Use the DMM to verify power and ground supply at the sensor connector (with the ignition on). To properly test the signal, an oscilloscope is recommended. With the sensor powered and the wheel rotating, observe the waveform generated by the sensor. A missing, distorted, or inconsistent square wave pattern indicates a sensor or tone ring issue.
6. Inspect and Verify Tone Ring Condition: If the sensor and wiring tests prove inconclusive, carefully inspect the ABS tone ring. This often requires removing the wheel, brake caliper, and rotor for a clear view. Look for cracks, bent teeth, missing teeth, or excessive buildup of rust, dirt, or metallic debris that could interfere with the sensor’s ability to accurately count rotations.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are commonly indicated for C1701:

• Replace the Left Rear Wheel Speed Sensor: If diagnostic tests confirm an internal fault within the sensor (e.g., incorrect resistance, no signal output, or a distorted waveform), replacement is the most frequent solution. Always use a high-quality OEM or equivalent aftermarket part to ensure compatibility and longevity. Ensure the sensor is properly seated and torqued to specifications.
• Repair or Replace Damaged Wiring Harness: If the wiring is found to be chafed, cut, or corroded, the damaged section must be professionally repaired. This involves soldering new wire segments, using appropriate gauge wiring, and protecting the repair with heat-shrink tubing and conduit. If the damage is extensive or involves multiple conductors, replacing the entire sub-harness or pigtail connector assembly is recommended.
• Clean or Replace Corroded Electrical Connectors: For connectors exhibiting corrosion, use an electrical contact cleaner and a small, non-abrasive brush to thoroughly clean the terminals. If the corrosion is severe and has compromised the terminal’s integrity or spring tension, the connector pigtail should be replaced. Apply dielectric grease upon reassembly to prevent future corrosion and enhance electrical contact.
• Clean or Replace Damaged ABS Tone Ring: If the tone ring is fouled with debris, carefully clean it using a suitable solvent and brush. If the tone ring is visibly damaged (cracked, bent, or missing teeth), it requires replacement. Depending on the vehicle’s design, this may involve replacing the entire axle shaft, wheel hub assembly, or in some cases, the tone ring itself can be pressed on.
• ABS Control Module Replacement: This should be considered only as a last resort, after all other potential causes (sensor, wiring, tone ring) have been meticulously ruled out. ABS control module replacement is often expensive and typically requires programming or calibration using specialized diagnostic equipment after installation.
• Post-Repair Procedures: After performing any repair, clear all stored DTCs using an OBD-II scanner. Perform a road test of the vehicle under varying conditions (including light to moderate braking) to allow the ABS module to complete its self-tests and confirm the repair. Monitor live data during the road test to ensure all wheel speed sensors are providing consistent and accurate readings.