C1700

What Does Code C1700 Mean?

The diagnostic trouble code C1700, typically associated with the chassis control systems, signifies an electrical malfunction within the circuit of the Left Rear Wheel Speed Sensor. The Anti-lock Braking System (ABS) control module, which may be an independent unit or integrated within the Powertrain Control Module (PCM) or Electronic Brake Control Module (EBCM), continuously monitors the electrical signals (voltage, frequency, or resistance) generated by each wheel speed sensor. These sensors provide critical rotational speed data for each wheel. When the ABS module detects an anomaly in the left rear wheel speed sensor’s circuit – such as an open circuit (disconnection), a short to ground, a short to voltage, or an implausible resistance reading – it interprets this as a circuit failure and sets the C1700 code. This circuit failure prevents the ABS module from accurately determining the rotational speed of the left rear wheel, thereby impairing the functionality of the ABS, Traction Control System (TCS), and Electronic Stability Control (ESC) systems.

Common Symptoms

• ABS Warning Light Illuminated: The most common and immediate symptom is the illumination of the ABS warning light on the instrument cluster.
• Traction Control System (TCS) Light Illuminated: Since the TCS relies on wheel speed data, its warning light will often illuminate in conjunction with the ABS light.
• Electronic Stability Control (ESC/VSC) Light Illuminated: The ESC system also depends on accurate wheel speed data; its warning light will likely activate.
• Loss of ABS Functionality: In the event of hard braking, the wheels may lock up, as the ABS system will be disabled or operate in a degraded mode.
• Erratic Speedometer Readings: While less common for a single rear wheel speed sensor, some vehicles use rear wheel speed data for speedometer input, potentially leading to inaccurate readings.
• Stiff Brake Pedal Feel: In some advanced brake-by-wire or electronic assist systems, a loss of critical sensor data can cause the brake pedal feel to change.

What Causes the Code C1700?

• Faulty Left Rear Wheel Speed Sensor: Internal electrical failure of the sensor’s magnetic pickup or Hall effect component, leading to an open circuit or incorrect signal output.
• Damaged Wiring Harness: Frayed, cut, chafed, or corroded wires within the left rear wheel speed sensor circuit. This can result from road debris, rodent damage, or exposure to environmental elements like water and road salt, leading to an open circuit, short to ground, or short to voltage.
• Corroded or Loose Electrical Connector: Poor connection at either the left rear wheel speed sensor itself or at the ABS control module, often caused by corrosion, bent pins, or inadequate terminal tension.
• Damaged Wheel Bearing Assembly (with Integrated Sensor): In many modern vehicles, the wheel speed sensor or its tone ring is integrated into the wheel bearing assembly. Excessive wear or damage to the bearing can compromise the sensor or its magnetic reluctor ring.
• Damaged Tone Ring/Reluctor Ring: A cracked, corroded, or missing tooth on the magnetic tone ring that the sensor reads can cause an intermittent or absent signal. While often resulting in an “implausible signal” code, severe damage can manifest as a circuit failure.
• Faulty ABS Control Module: Although less common, an internal failure within the ABS module’s circuitry responsible for processing the left rear wheel speed sensor input can also trigger C1700.

How to Diagnose and Troubleshoot

Diagnosis of C1700 requires a systematic approach, often involving a professional-grade OBD-II scanner and a digital multimeter (DMM).

1. Initial Scan and Data Review:
   • Connect an OBD-II scanner capable of reading ABS/chassis codes. Confirm C1700 is present and check for any related or accompanying codes.
   • Review freeze frame data for C1700, noting conditions (vehicle speed, engine RPM, etc.) when the code was set.
   • If the scanner supports live data for ABS wheel speeds, monitor the left rear wheel speed while driving slowly or spinning the wheel by hand (vehicle safely jacked). An erratic or zero reading confirms a signal issue.
2. Visual Inspection:
   • Safely raise and support the vehicle. Remove the left rear wheel.
   • Thoroughly inspect the left rear wheel speed sensor and its wiring harness from the sensor connection point at the hub back into the main vehicle harness. Look for visible damage such as cuts, chafing, corrosion, or signs of rodent activity.
   • Check the sensor’s electrical connector for security, corrosion, bent pins, or signs of water intrusion.
   • Inspect the tone ring (if visible and separate from the bearing) for cracks, missing teeth, or excessive debris.
   • Trace the wiring as far as possible towards the ABS control module, looking for any pinch points or areas of strain.
3. Electrical Testing with a Digital Multimeter (DMM):
   • Disconnect the vehicle battery before disconnecting any ABS module connectors to prevent damage to sensitive electronics.
   • Sensor Resistance Test (Passive Sensors): Disconnect the left rear wheel speed sensor connector. Using a DMM set to ohms, measure the resistance across the sensor’s terminals. Compare the reading to manufacturer specifications (typically 800-2500 ohms for passive sensors). An “OL” (open circuit) or a reading significantly outside the specified range indicates a faulty sensor. Active (Hall effect) sensors may not show a simple resistance reading; consult specific service information.
   • Wiring Continuity Test: Disconnect both ends of the left rear wheel speed sensor circuit – at the sensor and at the ABS module connector. Use the DMM in continuity mode to check each wire from one end to the other. There should be continuity (very low resistance, typically < 1 ohm). An "OL" indicates an open circuit (broken wire).
   • Short to Ground/Voltage Test: With both ends of the sensor wiring disconnected, check each wire for continuity to chassis ground. There should be no continuity (“OL”). Also, check for short to voltage by measuring voltage on each wire with the key ON (ABS module connected, but sensor disconnected). There should be no voltage present unless it’s a dedicated power supply line for an active sensor.
   • Voltage Supply Test (Active Sensors): If it’s an active sensor, reconnect the ABS module (and battery). With the sensor disconnected, turn the ignition ON and measure the voltage at the sensor’s harness connector. Active sensors typically receive a 5V or 12V reference voltage from the ABS module. Lack of this voltage suggests an issue with the ABS module’s output or a wiring fault in the power supply line.
4. ABS Module Test: If the sensor and all wiring tests confirm good functionality and integrity, the issue may lie within the ABS control module itself. This is often confirmed by specialized diagnostic tools or professional repair facilities.

Recommended Repairs and Solutions

Once the root cause of C1700 has been precisely identified through thorough diagnosis, the appropriate repair can be performed.

• Replace Left Rear Wheel Speed Sensor: If the sensor tests faulty (e.g., open circuit, incorrect resistance, no output signal), replacement is the primary solution. Ensure the correct sensor for your specific make, model, and trim is used, as there can be variations.
• Repair or Replace Damaged Wiring Harness: If the wiring is found to be cut, chafed, or corroded, carefully repair the damaged section using appropriate gauge wire, soldering connections, and protecting the repair with heat-shrink tubing and electrical tape or loom. For extensive damage, replacement of the entire harness section may be necessary.
• Clean or Repair Corroded/Loose Connectors: If corrosion or loose terminals are found, use electrical contact cleaner and a small pick or terminal tool to clean and restore proper connection. Apply dielectric grease to the terminals before reassembly to prevent future corrosion. Replace the connector if it is severely damaged.
• Replace Wheel Bearing Assembly: If the wheel speed sensor or its tone ring is integrated into the wheel bearing, and the bearing is worn or the tone ring is damaged, the entire wheel bearing assembly will need replacement. This is a common repair for rear wheel speed sensor issues.
• ABS Module Replacement/Repair: As a last resort, if all other components (sensor, wiring, connectors) have been thoroughly tested and confirmed to be in good working order, the ABS control module may require replacement or repair. This is typically the most expensive repair and may necessitate programming or coding by a professional after installation.

Important Mechanic’s Tips:

• Always disconnect the battery before working on electrical components of the ABS system.
• After completing any repairs, clear the diagnostic trouble codes using an OBD-II scanner.
• Perform a thorough road test to confirm the ABS, TCS, and ESC warning lights remain off and that the systems function correctly.
• Some vehicles may require an ABS system bleed or a sensor calibration procedure after sensor or module replacement; refer to the vehicle’s specific service manual.
• Consider inspecting the right rear wheel speed sensor and wiring as well, especially on vehicles operating in harsh environments, as similar issues can sometimes manifest symmetrically over time.