C1702

What Does Code C1702 Mean?

The diagnostic trouble code C1702, “Right Rear Sensor Circuit Short to Vbat,” indicates that the Anti-lock Braking System (ABS) control module, often integrated with the Brake Control Module (BCM) or Powertrain Control Module (PCM), has detected an electrical fault within the circuit for the right rear wheel speed sensor. Specifically, the module monitors the voltage on the sensor’s signal or power supply circuit and determines that it is receiving voltage consistent with the vehicle’s battery voltage (Vbat, typically 12-14 volts) when it should not be. This implies a direct short circuit from the sensor’s wiring or internal components to a constant positive voltage source, preventing the ABS module from accurately receiving or transmitting wheel speed data. This condition directly compromises the functionality of the ABS, Traction Control System (TCS), and Vehicle Stability Control (VSC) systems, as precise wheel speed information is critical for their operation.

Common Symptoms

• ABS Warning Light: The most common symptom is the illumination of the Anti-lock Braking System (ABS) warning light on the instrument cluster.
• Traction Control/Stability Control Light: The Traction Control System (TCS) and/or Vehicle Stability Control (VSC) warning lights may also illuminate, as these systems rely on wheel speed sensor data.
• Loss of ABS/TCS/VSC Functionality: The primary functional symptom is the disablement of ABS, TCS, and VSC features, potentially leading to conventional braking behavior without anti-lock protection during hard braking.
• Erratic Speedometer Reading: In some vehicles, particularly if the right rear sensor heavily contributes to overall vehicle speed calculation or is shared by other modules, an intermittent or erratic speedometer reading might occur, though this is less common for a hard short to Vbat.
• Transmission Shifting Issues: Less frequently, some vehicle transmissions may use wheel speed data for shift logic, and a compromised signal could potentially affect transmission performance.

What Causes the Code C1702?

• Damaged Wiring Harness: The most frequent cause is physical damage to the wiring harness leading to the right rear wheel speed sensor. This can include chafing, pinching, or melting of the insulation, causing the sensor signal wire or power wire to short directly to another power wire or a constant battery voltage source.
• Faulty Right Rear Wheel Speed Sensor: An internal short circuit within the wheel speed sensor itself can cause the signal or power output to be stuck at Vbat. This is more common with active sensors that receive a constant power supply.
• Corroded or Damaged Connector: Corrosion within the electrical connector for the right rear wheel speed sensor or at the ABS module connector can create a conductive bridge between the sensor circuit and a positive voltage pin, leading to a short to Vbat.
• Internal ABS/BCM Module Failure: In rare instances, the ABS control module (or BCM) itself may have an internal electronic fault that erroneously applies Vbat to the right rear wheel speed sensor circuit. This is typically a last resort diagnosis after ruling out external wiring and sensor issues.
• Improper Installation or Aftermarket Components: Recent repairs or the installation of aftermarket components that interfere with or incorrectly route the wheel speed sensor wiring can lead to a short.

How to Diagnose and Troubleshoot

Diagnosis of C1702 requires a methodical approach using a digital multimeter (DMM) and an advanced OBD-II scanner capable of accessing ABS module data.

1. Retrieve and Analyze DTCs: Connect an OBD-II scanner and confirm the presence of C1702. Check for any related codes that might point to a broader electrical issue. Access live data from the ABS module to observe the right rear wheel speed sensor’s voltage reading. A short to Vbat will often show a consistently high voltage (e.g., 12-14V) when the wheel is stationary or rotating slowly.
2. Perform a Thorough Visual Inspection:
   • Disconnect the vehicle’s battery for safety.
   • Visually inspect the entire wiring harness from the right rear wheel speed sensor connector to the ABS control module. Pay close attention to areas where the harness passes near suspension components, exhaust pipes, sharp edges, or through grommets. Look for signs of chafing, pinching, melting, or cuts in the insulation.
   • Inspect both the wheel speed sensor connector and the ABS module connector for bent pins, corrosion, water intrusion, or loose terminals.
3. Isolate and Test the Circuit (DMM):
   • Disconnect the right rear wheel speed sensor from its harness connector.
   • Using the vehicle’s wiring diagram, identify the power supply, ground, and signal wires for the right rear wheel speed sensor.
   • With the ignition OFF, measure the resistance between the suspected signal or power wire terminal in the harness side connector and a known vehicle chassis ground. A very low resistance reading (e.g., <5 ohms) could indicate a short to ground, which is not C1702, but important to rule out.
   • Reconnect the vehicle battery (carefully, ensuring no other circuits are shorted) and turn the ignition to the ON position (engine off). Measure the voltage between the suspected signal wire terminal in the harness side connector and a known good ground. If you measure battery voltage (Vbat) on the signal wire when it should be a lower reference voltage or fluctuate, this confirms the short to Vbat is within the harness or upstream module.
   • If no Vbat is found on the harness side signal wire, then the issue likely lies within the sensor itself. Proceed to sensor testing.
4. Test the Wheel Speed Sensor:
   • With the sensor disconnected from the harness, measure the internal resistance of the sensor (for passive sensors). Consult service information for expected resistance values. An open circuit or a dead short within the sensor indicates internal failure.
   • For active sensors (typically 3-wire: power, ground, signal), it’s more challenging to test static. You would ideally need to supply power and ground to the sensor and then monitor its signal output with an oscilloscope while manually rotating the wheel. However, given a “short to Vbat” symptom, an internal short might present itself as Vbat on the signal output even when stationary, or a very high current draw if power is supplied.
5. Wiggle Test: If intermittent, with the DMM connected for voltage monitoring (back-probing the suspected shorted wire), gently wiggle the wiring harness, connectors, and sensor itself while observing the DMM readings. A fluctuation or momentary return to normal voltage can pinpoint the location of an intermittent short.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs and solutions are recommended:

1. Repair or Replace Damaged Wiring Harness: If the visual inspection or DMM tests reveal a shorted wire in the harness, the most effective solution is to repair the damaged section. Use appropriate gauge wire, solder connections, and insulate with marine-grade heat shrink tubing to ensure durability. For extensive or inaccessible damage, replacing the entire wheel speed sensor harness segment may be necessary. Ensure proper routing and securement of the new wiring to prevent future damage.
2. Replace Faulty Right Rear Wheel Speed Sensor: If diagnostic testing confirms an internal short within the wheel speed sensor, replace the sensor with a new, OEM-quality unit. Ensure the mounting surface is clean and free of rust or debris to ensure proper sensor gap.
3. Clean or Replace Corroded Connectors: If corrosion is found at the sensor or ABS module connector, use a specialized electrical contact cleaner and a small brush to thoroughly clean the terminals. If the corrosion is severe, or pins are bent/damaged, replace the affected connector or the entire pigtail section of the harness. Apply dielectric grease to the terminals upon reassembly to prevent future corrosion.
4. Replace ABS/BCM Control Module: Only if all other components (wiring, sensor, connectors) have been thoroughly tested and confirmed to be in good working order, and the short to Vbat persists from the module’s output, should the ABS/BCM module be considered faulty. Module replacement is often an expensive repair and may require programming or calibration specific to the vehicle after installation.
5. Clear DTCs and Test Drive: After performing any repairs, clear the diagnostic trouble code using an OBD-II scanner. Conduct a thorough road test of the vehicle, including varied braking scenarios, to confirm that the code does not return and that the ABS, TCS, and VSC warning lights remain off.