P0143 The bank 1 sensor 3 oxygen sensor is reporting a voltage that is too low

O2 sensor circuit low voltage, bank 1 sensor 3

Severity not verified — if the car runs badly, have it inspected

The sources read for this code do not rate its urgency, so no severity is claimed. TroubleCodes.net describes the usual symptom as a check engine light, sometimes with poorer fuel economy or running; have it diagnosed rather than ignoring it.

Source: how we rate severity

P0143 in short

P0143 means the heated oxygen sensor circuit on bank 1, sensor 3 is reading low voltage. TroubleCodes.net names the sensor as the most common cause, followed by damaged wiring or connectors and exhaust leaks. It usually only lights the check engine light.

The Delaware DMV list and TroubleCodes.net both title P0143 as an O2 sensor circuit low voltage on bank 1 sensor 3. TroubleCodes.net says the sensor monitors exhaust oxygen downstream of the catalytic converter.

TroubleCodes.net says drivers typically notice only the warning light, because this is an emissions-control function rather than an engine-critical one.

Listed causes are a faulty sensor, damaged wiring or connectors from debris or corrosion, exhaust leaks between the converter and sensor, and computer circuit issues.

Most likely causes

These are general causes for this code across vehicles. None is specific to one make or model.

  1. Faulty or contaminated bank 1 sensor 3

    Common general cause
    Why it ranks here
    TroubleCodes.net lists the oxygen sensor itself as a leading cause, with a typical life under five years on some of its pages.
    What would change this
    Rises if the sensor's resistance is out of specification or its live data is stuck. Falls if the sensor tests within spec and the wiring is faulty.
    How to test the oxygen (o2) sensor

  2. Damaged, burned, corroded or disconnected wiring, connector or fuse

    Common general cause
    Why it ranks here
    The page lists wiring, connector and fuse faults caused by heat, road debris or corrosion.
    What would change this
    Rises if the harness is damaged or the connector is corroded or loose, or continuity fails. Falls if all circuit tests pass.

  3. Exhaust leak between the converter and the sensor

    Possible — needs testing
    Why it ranks here
    The page lists exhaust leaks between the converter and the sensor, which let outside air reach it.
    What would change this
    Rises if a leak or soot track is found near the sensor. Falls if the exhaust is tight.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all codes and freeze-frame data with a scan tool and record them before clearing.

    Low riskTool: OBD-II scan tool

    • IfOther oxygen sensor codes are stored

      It meansCheck shared wiring and fuses first.

      Go to step 2

    • IfP0143 is the only code

      It meansInspect the sensor wiring and look for exhaust leaks.

      Go to step 2

  2. With the exhaust cold, inspect the fuses, harness, connector and sensor for damage or corrosion and check the exhaust for leaks near the sensor.

    Use cautionTool: flashlight; fuse tester

    Warning:Exhaust parts and the sensor stay hot long after the engine is off and can cause serious burns. Work only on a cold exhaust and never under a car held up only by a jack.

  3. Use a multimeter to check circuit continuity (about 1 ohm or less end to end, and over 10 kilo-ohms to ground) and the sensor's internal resistance, then compare live sensor data.

    Use cautionTool: digital multimeter; scan tool

    Warning:Disconnect the sensor before testing resistance and keep the probes off live circuits. Use the figures for your own vehicle where the manual gives them; TroubleCodes.net's values are general.

Symptoms

  • Check engine light, often with no other change in how the car drives

How to fix

  1. With the exhaust fully cold, inspect the sensor wiring, connector and fuses for damage or corrosion.

  2. Check the exhaust between the converter and the sensor for leaks.

Parts and cost context

  • Oxygen (O2) sensor:Replace the sensor only after wiring, fuses and exhaust leaks are checked. Use the part made for that bank and position. Labour varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

We don't have reviewed vehicle-specific evidence for P0143 yet. The causes and tests above apply across vehicles.

  • P0144The bank 1 sensor 3 oxygen sensor is reporting a voltage that is too high

    Same system Possible — needs testing

    P0144 is the high-voltage code for the same bank 1 sensor 3 circuit; the sensor and wiring checks are the same.

  • P0142The bank 1 sensor 3 oxygen sensor circuit is giving the computer a signal outside what it expects

    Same system Possible — needs testing

    P0142 is the general circuit malfunction code for the same sensor.

All Oxygen sensors codes

P0143 questions

What does bank 1 sensor 3 mean?

Bank 1 is the side of the engine with cylinder 1. Sensor 3 is a third oxygen sensor on that bank; TroubleCodes.net describes it as monitoring exhaust oxygen downstream of the catalytic converter, so look at your vehicle's wiring diagram for its exact position.

Sources and review

  1. P0143 trouble code page — TroubleCodes.net
  2. On-Board Diagnostic Trouble Codes (generic code title list) — Delaware Division of Motor Vehicles
Last reviewed
Written by
Saurabh K.
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