C1704

What Does Code C1704 Mean?

DTC C1704 indicates a detected electrical fault within the circuit of the Right Rear Wheel Speed Sensor. As a “C” code (Chassis code), it primarily pertains to components of the Anti-lock Brake System (ABS), Traction Control System (TCS), and Vehicle Stability Assist/Control (VSA/VSC). The ABS Control Module (also known as the Electronic Brake Control Module or EBCM), which typically monitors the wheel speed sensors, has identified an anomaly in the electrical signal or continuity of the circuit for the right rear wheel speed sensor. This typically means the module is not receiving a plausible signal, or any signal at all, from the sensor, suggesting an open circuit, short circuit, or an internal sensor failure. When this fault is detected, the ABS/TCS/VSA systems are usually disabled, illuminating corresponding warning indicators on the instrument cluster.

Common Symptoms

• ABS Warning Light: The Anti-lock Brake System warning indicator will be illuminated on the dashboard.
• Traction Control/Stability Control Warning Light: The TCS and/or VSA/VSC warning indicators will likely be illuminated, indicating these systems are inoperative.
• Loss of ABS/TCS/VSA Functionality: In an emergency braking situation or during loss of traction, the systems designed to prevent wheel lock-up or excessive wheel spin will not activate.
• Cruise Control Malfunction: Some vehicle systems rely on wheel speed sensor inputs for cruise control operation; thus, it may be disabled.
• Erratic Speedometer Readings: While less common for a single rear wheel speed sensor, some systems may experience intermittent or incorrect speedometer readings if this sensor contributes to vehicle speed calculation.

What Causes the Code C1704?

• Faulty Right Rear Wheel Speed Sensor: The sensor itself may have an internal electrical failure, such as an open circuit in its winding or a damaged semiconductor within active sensors.
• Damaged Wiring Harness: An open circuit (broken wire), short to ground, or short to voltage in the wiring harness connecting the right rear wheel speed sensor to the ABS control module. This can be caused by physical damage, corrosion, or pinching.
• Corroded or Loose Electrical Connector: Poor electrical contact at the sensor connector or at the ABS module connector due to corrosion, dirt, or improper seating.
• Damaged Tone Ring/Reluctor Wheel: Although often leading to a “plausibility” or “signal input” code, severe damage to the tone ring (missing teeth, cracks, excessive runout) can result in the ABS module interpreting the lack of a proper signal as a circuit fault.
• Excessive Wheel Bearing Play: Significant play in the right rear wheel bearing can cause the tone ring to move too far from the sensor, leading to an inconsistent or absent signal, which might be interpreted as a circuit fault.
• Faulty ABS Control Module: While less common, an internal failure within the ABS control module’s input circuit for the right rear wheel speed sensor can trigger this code.

How to Diagnose and Troubleshoot

Diagnosis of C1704 requires a methodical approach, utilizing an OBD-II scan tool and a digital multimeter (DMM).

1. Visual Inspection: Begin with a thorough visual inspection of the right rear wheel speed sensor, its mounting, and the entire wiring harness leading from the sensor to the nearest junction or directly to the ABS module. Look for signs of physical damage, cuts, chafing, corrosion, or loose/damaged connectors. Inspect the tone ring (if visible) for damage or debris.
2. Scan Tool Data Analysis:
   • Connect an advanced OBD-II scan tool capable of accessing ABS system live data.
   • Clear the C1704 DTC and test drive the vehicle. Observe if the code immediately returns.
   • Monitor the live data stream for all four wheel speed sensors while driving at various speeds (e.g., 5-20 mph). Compare the right rear sensor’s reading to the other three. A faulty circuit will likely show 0 mph, an erratic/intermittent reading, or an implausible value compared to the other wheels.
   • Check freeze frame data associated with the C1704 code to understand the operating conditions (vehicle speed, engine load, etc.) when the fault was first detected.
3. Digital Multimeter (DMM) Testing:
   • Sensor Resistance Test (Passive Sensors): Disconnect the right rear wheel speed sensor. Using a DMM, measure the resistance across the two signal pins of the sensor. Compare this reading to manufacturer specifications (typically a few hundred ohms to several kOhms). An open circuit (DMM reads OL or infinite resistance) or a short circuit (very low resistance, near 0 ohms) indicates an internal sensor failure. Note: Active (hall effect or magnetoresistive) sensors cannot be reliably tested for resistance alone as they require voltage to operate.
   • Sensor Voltage/Signal Test (Active Sensors): For active sensors, reconnect the sensor and backprobe the signal wire while the ignition is on (if powered by ignition) or the engine is running. With the right rear wheel safely lifted and spun by hand or slowly by the vehicle, use an oscilloscope to observe the AC voltage signal (for AC type sensors) or a square wave pulse (for active sensors). A DMM can sometimes catch changes in voltage for active sensors if set to AC voltage, but an oscilloscope provides a clearer picture of signal integrity.
   • Wiring Harness Continuity Test: Disconnect both the sensor and the ABS module connector. Use the DMM to test for continuity between the corresponding pins of the right rear wheel speed sensor circuit at both ends of the harness. Look for open circuits. Test for resistance between each wire of the sensor circuit and vehicle ground, and between each wire and battery positive. There should be infinite resistance (OL) in both cases, indicating no shorts.
   • Power and Ground Supply Test (Active Sensors): With the ABS module connected (and power to the module), check for proper voltage supply and ground at the right rear wheel speed sensor connector (with the sensor disconnected). Refer to wiring diagrams for specific pinouts.
4. Wheel Bearing and Tone Ring Inspection: If the sensor and wiring test positive, thoroughly inspect the right rear wheel bearing for excessive play (rocking the wheel top-to-bottom and side-to-side while lifted). Inspect the tone ring for any signs of damage, cracks, or debris lodged between the tone ring and the sensor.

Recommended Repairs and Solutions

Based on diagnostic findings, the following repairs are typically performed to resolve DTC C1704:

• Replace Right Rear Wheel Speed Sensor: This is the most common resolution if the sensor itself fails electrical tests or shows no plausible signal during live data monitoring. Ensure the replacement sensor is an OEM equivalent or meets manufacturer specifications for proper operation.
• Repair or Replace Wiring Harness: If the wiring harness is found to be damaged (open, shorted, or chafed), repair the damaged section using appropriate automotive-grade wire, solder, heat shrink, and protective loom. If damage is extensive, replace the entire segment of the harness. Ensure connections are secure and weatherproof.
• Clean and Secure Electrical Connectors: If corrosion or poor contact is identified, clean the terminals of both the sensor and harness connectors using electrical contact cleaner and a small brush. Apply dielectric grease to prevent future corrosion and ensure the connectors are fully seated and locked.
• Replace Damaged Tone Ring or Wheel Bearing: If the tone ring is cracked, bent, or has missing teeth, or if there is excessive wheel bearing play causing sensor signal issues, these components must be replaced. This often involves replacing the entire wheel hub assembly, depending on the vehicle design.
• Replace ABS Control Module: Only consider replacing the ABS control module after thoroughly ruling out the sensor, wiring, and tone ring/wheel bearing as the culprits. ABS module replacement often requires programming or calibration with a factory-level scan tool.
• Clear Codes and Test Drive: After any repair, clear the DTC C1704 and perform an extended test drive under varying conditions, including moderate braking, to confirm the repair and ensure the ABS, TCS, and VSA/VSC warning lights remain off.