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OBD-II Code

P0043

Severity

Not yet reviewed

Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.

Can you drive it

We cannot say

Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.

Indicative cost (USD)

$50–$350

From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.

P0043 sets when the ECU detects a 'circuit low' fault on the bank-1 sensor-3 (the second downstream O2 sensor on vehicles with three O2 sensors per bank, such as some Toyota, Lexus, and certain heavy-duty applications) heater control circuit - the heater driver is reading a stuck-low control voltage or unable to verify heater current draw.

How a shop works this

Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.

  1. Note every code that is set, not just this one.

    Codes that appear together usually narrow the cause faster than any one of them read alone.

  2. Read the freeze frame — the conditions the fault was recorded under.

    Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.

  3. Confirm the fault is current rather than history.

    Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.

  4. Then follow the diagnostic notes further down this page, in the order they are written.

    They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.

If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.

Common symptoms

  • Check engine light
Read the full diagnostic procedureP0043 sets when the ECU detects a 'circuit low' fault on the bank-1 sensor-3 (the second downstream O2 sensor on vehicles with three O2 sensors per b…

P0043 sets when the ECU detects a 'circuit low' fault on the bank-1 sensor-3 (the second downstream O2 sensor on vehicles with three O2 sensors per bank, such as some Toyota, Lexus, and certain heavy-duty applications) heater control circuit - the heater driver is reading a stuck-low control voltage or unable to verify heater current draw. Sensor 3 is rare in light-duty service but appears on vehicles with multiple catalysts in series (close-coupled + underbody) where additional monitoring is needed for emissions compliance.

Cheapest-first ladder

  1. Confirm the vehicle actually has a sensor 3 (not all platforms wire one even if the connector is provisioned) and locate it - usually the rearmost O2 sensor in the exhaust path.
  2. Check the heater fuse and the connector at the sensor for melt damage from heat shield loss.
  3. DMM the heater resistance pin-to-pin - typical 3-15 ohms; OL means the heater element is dead.
  4. DMM the harness control wire for short-to-ground with the sensor unplugged. Expensive-misdiagnosis trap: replacing the closer downstream O2 sensor (sensor 2) thinking the numbering follows the dash-display convention - sensor 3 is its own physical component.
Vehicle-specific patterns2007-2013 Toyota Tundra / Sequoia 5.7L 3UR-FE throws P0043 from a melted bank-1 third-O2 sensor connector aft of the underbody cat.
  • 2007-2013Toyota Tundra / Sequoia 5.7L 3UR-FE throws P0043 from a melted bank-1 third-O2 sensor connector aft of the underbody cat.
  • 2008-2014Lexus LX570 with the 5.7L throws P0043 from genuine heater element failure on the rearmost bank-1 sensor after long service.
  • 2010-2016Toyota Sienna 3.5L 2GR-FE throws P0043 from chafed wiring at a body-mount clip.
  • 2011-2017Toyota Camry / Highlander with the 2GR-FE V6 (when equipped with the 3-sensor configuration for CARB markets) throws P0043 after exhaust work where the rear sensor harness gets dragged.

Estimated repair$50 to $350

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