C1700 — Left Rear Sensor Circuit Failure

What are the symptoms of C1700?

Drivers most often notice: increased fuel consumption in some cases, possible limp mode depending on the affected component, Check Engine Light on, the affected system operates intermittently or not at all.

How do I diagnose C1700 myself?

Start with a scan: confirm C1700, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the left rear sensor circuit, and verify the suspect component against live data before buying parts.

What is the most common cause of C1700?

The most common causes are: faulty sensor or actuator of the affected circuit, open or shorted wiring in the circuit, control module driver fault.

Will C1700 clear itself?

Sometimes C1700 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How much does it cost to fix C1700?

Repair wiring or connectors — $80–$250; Replace the faulty sensor or actuator — $150–$500; Control module repair — $300–$1,000. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

When your scan tool pulls code C1700, it means the vehicle's control unit has detected a problem with the left rear sensor circuit. Specifically, the module sees one or more of the sensors or actuators in that circuit operating outside the factory-calibrated voltage or resistance range. Technically described as "Left Rear Sensor Circuit Failure," this code falls under the chassis systems category, which covers brakes, steering, and suspension components rather than the engine itself.

The affected system varies by vehicle make and model — it could be a wheel speed sensor, a suspension position sensor, a brake pressure transducer, or another chassis-related device mounted at the left rear corner. Regardless of the specific component, the ECU monitors that circuit constantly while you drive. When the signal strays outside acceptable parameters, the module logs the fault and, if the condition persists across multiple ignition cycles, illuminates the check engine light.

It's important to understand that C1700 rarely sets on a single bad reading. The control unit requires the fault to appear repeatedly under specific driving conditions before it triggers the warning lamp. That's why the freeze frame data stored alongside C1700 is so valuable — it captures engine load, RPM, vehicle speed, and temperature at the exact moment the problem occurred. Replicating those conditions during diagnosis helps you catch an intermittent fault that might otherwise vanish when the car sits in the shop.

Symptoms of C1700

When C1700 is active, you may notice one or more of the following:

• Check Engine Light or dedicated warning lamp illuminated on the dashboard
• The specific system tied to the left rear sensor operates intermittently or stops working entirely
• Reduced vehicle performance or limp-mode operation in severe cases
• Minor increase in fuel consumption if the ECU alters engine or transmission behavior in response
• Unusual behavior from related safety systems, depending on which sensor or circuit is affected

Common Causes

The root cause of C1700 typically falls into one of these categories, listed from most to least frequent:

• Wiring damage — chafing, melting, or broken wires in the left rear sensor circuit
• Connector problems — corrosion, bent pins, loose terminals, or moisture intrusion at the sensor or ECU connection
• Failed sensor or actuator — the component itself has stopped functioning correctly
• Blown fuse — a failed fuse interrupts power or ground to the affected circuit
• Poor ground connection — inadequate grounding causes signal abnormalities
• Control module issue — the driver inside the ECU that handles that circuit has failed

Diagnosing C1700

Follow these steps to pinpoint the fault without replacing parts unnecessarily:

1. Connect an OBD2 scanner, confirm C1700 is stored in the module's memory, and record all freeze frame data. This snapshot tells you the vehicle speed, engine load, and conditions present when the failure occurred.
2. Pull any related trouble codes. Additional C0xxx codes in the same module often point to shared power supplies, grounds, or communication lines. Also search for TSBs (Technical Service Bulletins) specific to your make, model, and year — many sensor circuit issues have documented factory fixes or software updates.
3. Perform a thorough visual inspection of the wiring harness and connectors for the left rear sensor circuit. Look for damaged insulation, corrosion buildup, broken wires, and any signs of prior repairs that may have been done poorly.
4. At the component connector, measure reference voltage, ground resistance, and signal continuity with a multimeter. Compare your readings against the specifications in the vehicle service manual.
5. While monitoring live data on the scanner, wiggle and flex the harness. If the signal drops out or fluctuates, you've identified a broken wire or intermittent connector.
6. Clear the code, then drive the vehicle through a complete drive cycle — especially replicating the conditions from the freeze frame — and verify C1700 does not return.

Repair Options and Costs

Once you've isolated the faulty component, here are typical repair scenarios with price ranges based on independent shop labor rates in the United States:

• Wiring or connector repair: Repairing damaged wires or cleaning/replacing corroded connectors typically runs $80 to $250, depending on whether you do the work yourself or pay a technician for an hour or two of labor.
• Sensor or actuator replacement: If the component itself has failed, expect to pay $150 to $500 for the part plus installation labor. Some sensors are simple plug-and-play units; others require wheel well or suspension disassembly.
• Control module repair or replacement: When the ECU's driver circuit for the left rear sensor has failed, module-level repair or replacement ranges from $300 to $1,000, including programming if needed.

Total Cost to Fix C1700

Taking all repair scenarios into account, fixing C1700 generally costs between $80 and $1,000 depending on what actually failed. The vast majority of cases involve wiring or connector issues on the lower end of that range. Spending time on a careful diagnosis before buying parts almost always saves money — the control module replacement scenario is the least common and should only be considered after you've ruled out every external cause.

Can You Drive with C1700?

In most situations, the vehicle remains driveable with C1700 stored. You may experience reduced performance, an illuminated warning light, or a disabled auxiliary system, but the car will typically continue operating. However, if the fault causes stalling, no-start conditions, or affects brake or steering-related sensors, treat it as urgent and have it diagnosed immediately. Don't ignore the code indefinitely — an unresolved sensor failure can compromise safety systems that depend on accurate data.

Related OBD2 codes

• C1701: Left Rear Sensor Circuit Fault
• C1702: RightRear Sensor Circuit Short to Vbat
• C1703: Right Rear Sensor Circuit Failure
• C1704: Right Rear Sensor Circuit Fault
• C1705: Left Rear Center Sensor Circuit Short to Vbat
• C1706: Left Rear Center Sensor Circuit Failure