P0143 is a generic OBD-II trouble code indicating that the ECM/PCM has detected a low voltage condition in the Bank 1 Sensor 3 oxygen sensor circuit. The exact sensor location and circuit configuration vary by vehicle.
P0143 Fault Code Description
P0143 means the oxygen sensor signal from Bank 1 Sensor 3 is lower than the expected range under the operating conditions being monitored by the engine control module.
Code: P0143
System: Powertrain / Emissions
Sensor: Bank 1 Sensor 3
Condition: Low Voltage
P0143 Vehicles Affected
P0143 can occur on vehicles equipped with a Bank 1 Sensor 3 oxygen sensor. Sensor numbering and exhaust-system configuration vary by engine, model year, emissions system, and manufacturer.
- Some Toyota and Lexus vehicles
- Some Nissan and Infiniti vehicles
- Some Honda and Acura vehicles
- Some Ford and Lincoln vehicles
- Some Chevrolet and GMC vehicles
- Some Dodge, Chrysler, and Jeep vehicles
- Other vehicles equipped with multiple oxygen sensors
Always verify the exact B1S3 location and wiring configuration using vehicle-specific service information.
P0143 Symptoms
- Check Engine Light
- Reduced fuel economy may occur
- Increased exhaust emissions
- Possible emissions-test failure
- Possible changes in fuel-trim behavior
- Usually limited drivability symptoms
P0143 Common Causes
- Faulty Bank 1 Sensor 3 oxygen sensor
- Signal wire shorted to ground
- Damaged or corroded sensor connector
- Open or damaged signal circuit
- Sensor wiring damaged by exhaust heat
- Poor sensor ground
- Exhaust leak affecting sensor operation
- Electrical circuit problem
- Rare ECM/PCM fault
A low oxygen-sensor signal does not automatically mean the sensor itself has failed. The circuit and exhaust system should be tested before replacement.
P0143 Severity
Low to Moderate. P0143 usually does not cause an immediate loss of vehicle control, but it can affect emissions and engine-management calculations. The fault should be diagnosed rather than ignored for an extended period.
P0143 Average Repair Cost
A typical P0143 repair may cost approximately $100–$400. A wiring or connector repair can cost less, while an oxygen sensor replacement can cost more depending on the vehicle.
Actual cost varies by vehicle, parts availability, labor rate, and the cause of the fault. This is a general estimate, not a vehicle-specific quote.
P0143 Diagnosis
P0143 Visual Inspection
Inspect the Bank 1 Sensor 3 connector and wiring. Look for corrosion, loose terminals, broken wires, melted insulation, or wiring contacting hot exhaust components.
P0143 Scan Tool and Live Data
Monitor B1S3 oxygen-sensor data after the engine reaches the required operating temperature. Compare the sensor behavior with related sensor and fuel-trim data according to the manufacturer's specifications.
P0143 Signal Circuit Test
Use the vehicle-specific wiring diagram to identify the sensor signal and ground circuits. Check for an unwanted connection to ground and verify circuit continuity where applicable.
P0143 Exhaust Inspection
Inspect the exhaust system around the sensor for leaks, damaged components, or conditions that could affect oxygen-sensor readings.
P0143 Wiring Diagram
O2 Signal ━━━━━━━━━━━━► ECM
Sensor Ground ━━━━━━━━━━━━► ECM Ground
Simplified circuit illustration. Actual wiring varies by vehicle.
P0143 Pinout
Signal ━━━━━━ ECM Signal Input
Ground ━━━━━━ Sensor Ground
Heater Power ━━━━━━ Heater Circuit
Pin numbers and wire colors vary by vehicle. Do not use a generic pinout as a substitute for the vehicle-specific wiring diagram.
P0143 Signal Circuit Voltage Test
When the B1S3 oxygen sensor signal is abnormally low, disconnect the sensor from the wiring harness and check the signal circuit according to the vehicle manufacturer's specifications.
With the sensor disconnected, a low signal may indicate a short to ground, damaged wiring, connector contamination, or another circuit fault.
If the signal returns to normal after disconnecting the sensor, the sensor may be pulling the signal low and should be tested according to the manufacturer's specifications.
Check the sensor ground, connector terminals, exhaust condition, and sensor operation before replacing the sensor.
P0143 Oscilloscope – Normal Signal
Illustrative waveform only. Actual signal characteristics depend on the sensor and vehicle.
P0143 Oscilloscope – Low Signal
Illustrative low-level signal pattern.
P0143 Oscilloscope – No Signal
A flat signal can indicate a sensor, circuit, or testing problem and must be verified using the manufacturer's diagnostic procedure.
P0143 Repair Verification
After the repair, clear the code and operate the vehicle under the conditions required by the manufacturer. Confirm that P0143 does not return and that the oxygen-sensor data behaves normally.
P0143 Common Repairs
- Repair damaged oxygen-sensor wiring
- Repair a shorted signal circuit
- Repair or replace a damaged connector
- Repair a sensor ground problem
- Repair an exhaust leak
- Replace the B1S3 oxygen sensor when testing confirms failure
- Repair a confirmed ECM/PCM circuit problem
P0143 Related Codes
- P0140 – O2 Sensor Circuit No Activity Detected (Bank 1, Sensor 2)
- P0141 – O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)
- P0142 – O2 Sensor Circuit Malfunction (Bank 1, Sensor 3)
- P0144 – O2 Sensor Circuit High Voltage (Bank 1, Sensor 3)
- P0145 – O2 Sensor Circuit Slow Response (Bank 1, Sensor 3)
- P0146 – O2 Sensor Circuit No Activity Detected (Bank 1, Sensor 3)
- P0147 – O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 3)
P0143 FAQ
P0143 – What does the code mean?
P0143 indicates a low voltage condition in the Bank 1 Sensor 3 oxygen sensor circuit.
P0143 – Does it mean the O2 sensor is bad?
Not necessarily. A short to ground, wiring problem, connector fault, ground problem, or exhaust issue can also cause a low sensor signal.
P0143 – Can I drive with the code?
The vehicle will often remain driveable, but the problem should be diagnosed because emissions and engine-management operation can be affected.
P0143 – Where is Bank 1 Sensor 3?
The exact location depends on the vehicle's engine and emissions configuration. Verify the B1S3 location using vehicle-specific service information.
P0143 – Should I replace the oxygen sensor?
Do not replace the sensor based on the code alone. Test the signal circuit, wiring, connector, ground, and exhaust system first.
P0143 Final Result
P0143 indicates that the ECM/PCM is detecting a low voltage condition from the Bank 1 Sensor 3 oxygen sensor circuit. Start with a visual inspection, then check live data, wiring, signal voltage, grounds, and the exhaust system before replacing the sensor. Always use the vehicle-specific wiring diagram and diagnostic specifications for the final diagnosis.
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