What Does P0043 Mean?
The PCM has detected that the heater circuit for the heated oxygen sensor (Bank 1, Sensor 3) is reading lower voltage or current than expected. Sensor 3 is the downstream post-catalytic converter sensor used primarily for catalyst efficiency monitoring. The driver may notice a check engine light and potentially increased emissions, though driveability is typically unaffected since this sensor is primarily for monitoring rather than fuel trim control.
Common Causes
40%
Failed O2 sensor heater element (open or high-resistance internal heater winding)
25%
Corroded, damaged, or disconnected wiring/connector at the O2 sensor
20%
Blown fuse or open relay in the O2 heater power supply circuit
15%
PCM heater driver circuit failure (low-side driver not providing proper ground)
Diagnostic Steps
1
Check freeze frame data for operating conditions when the code set — note coolant temp and engine run time to confirm the heater should have been active.
2
Locate the Bank 1 Sensor 3 O2 sensor (downstream of the catalytic converter). Disconnect the sensor and measure the heater element resistance across the heater pins — expect 3–15 ohms depending on application; infinite resistance indicates an open heater.
3
With the sensor disconnected and key on engine off (KOEO), verify battery voltage (12V+) is present at the heater power supply wire using a multimeter.
4
Check the ground side of the heater circuit for continuity back to the PCM heater driver pin — resistance should be less than 1 ohm.
5
Inspect the wiring harness for heat damage, chafing, or corrosion especially near the exhaust manifold and any routing clips.
6
If power, ground, and sensor heater resistance all test good, suspect a PCM heater driver failure — monitor the heater command with live data to confirm the PCM is attempting to activate the circuit.
Estimated Repair Cost
$100 - $350
Parts + labor, varies by vehicle and location
The PCM has detected that the heater circuit for the heated oxygen sensor (Bank 1, Sensor 3) is reading lower voltage or current than expected. Sensor 3 is the downstream post-catalytic converter sensor used primarily for catalyst efficiency monitoring. The driver may notice a check engine light and...
The most common cause of P0043 (HO2S Heater Control Circuit Low (Bank 1, Sensor 3)) is: Failed O2 sensor heater element (open or high-resistance internal heater winding)
Typical repair costs for P0043 range from $100 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to continue driving. This sensor is a monitoring sensor (post-catalyst) and does not directly affect fuel trim. The primary risk is increased tailpipe emissions and a failed emissions inspection. No immediate safety concern.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0043 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions / Exhaust
Difficulty
Type
Generic (SAE)
Recommended Tools
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