C1701

Left Rear Sensor Circuit Fault

Chassis Chassis/Safety ABS Wheel Speed Sensor 🔴 Serious — Stop or limit driving 🚫 Do Not Drive
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What This Actually Means

In plain language — no jargon

Your left rear wheel speed sensor isn't sending proper signals to the ABS/stability system. Think of it like a speedometer that's broken—the system can't tell how fast that wheel is spinning.

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Symptoms You May Notice

3 known symptoms for this code
ABS warning light illuminated on dashboard
Stability control or traction control disabled or warning active
Possible loss of ABS braking during emergency stops
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors voltage and signal frequency from the left rear wheel speed sensor to detect wheel slip and control anti-lock braking. The sensor generates an AC signal proportional to wheel rotation speed. A fault is detected when signal voltage, frequency, or waveform falls outside expected parameters.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Sensor voltage signal 0.2–5V AC, proportional to wheel speed No signal, erratic voltage, or constant high/low state
Signal frequency consistency Increases with wheel speed, smooth transitions Missing pulses, dropouts, or noise above threshold
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Left rear wheel speed sensor connector
Inspect and reseat the connector at the sensor; corrosion or loose pins often cause circuit faults.
2
Wheel speed sensor wiring harness
Check the wiring for cuts, abrasions, or moisture damage between sensor and ABS module.
3
Left rear wheel speed sensor
Replace the sensor if connector and wiring are sound; sensor internal failure is common.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code C1701 is classified as a serious fault. If your check engine light is flashing — not just steady — pull over safely and do not continue driving. A flashing CEL indicates an active misfire or critical failure that can cause catalytic converter damage within minutes or permanent engine harm within miles. Contact a certified mechanic immediately. Do not attempt roadside repairs on high-severity codes unless you are trained to do so.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code C1701

What happens after you fix the fault

Once the fault is repaired, C1701 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.