Generic fault code
P0043 — HO2S heater (bank 1, sensor 3), control circuit: signal low
The control unit stores code P0043 when it detects this fault: “HO2S heater (bank 1, sensor 3), control circuit: signal low”.
Indicative severity: MediumEmission control
Reviewed by Daniel Morales, founder of Reprorace SL, on
What does code P0043 mean?
The catalytic converter, oxygen sensors, EGR, fuel vapor system (EVAP), particulate filter and NOx reduction clean the exhaust. A fault here raises pollution and may make the car fail its inspection; left alone, some end in a bigger fault or in limp-home mode.
- System
- P · Powertrain
- Area
- Emission control · Car system: Exhaust and emissions
- Type
- Generic (SAE J2012 / ISO 15031-6): the same meaning on every make
- Indicative severity
- Medium. Diagnose soon: it may raise emissions or consumption, or trigger limp-home mode.
What usually causes code P0043?
- Short circuit to ground
- Loose or corroded connector, backed-out terminals
- Damaged, chafed or pinched wiring
The most likely causes come first. Only a check on the car confirms which one is yours.
What are the symptoms of code P0043?
- Often nothing you notice while driving
- Higher fuel use
- Higher emissions: the inspection may not go well
These are the usual symptoms of this kind of fault: not all of them always appear, and sometimes you notice nothing.
Can I keep driving with code P0043?
With care, and not for long. You can take the car to a workshop, ideally without long trips or heavy loads, and without putting it off: fuel use or emissions may rise and the car may go into limp-home mode (less power). If the light flashes, a red warning light comes on, the temperature rises or you notice a loss of power, noises or smoke, stop as soon as it is safe.
This is guidance only: only someone who checks the car can say whether it is safe to drive.
An indicative description of the code's generic meaning. Each manufacturer may give it a different meaning, conditions or tests: always follow its service information and your workshop's advice.
What you can do yourself
For this kind of fault
With the engine cold, look whether the oxygen sensor's wire and connector (under the car, by the exhaust) are damaged or loose. If the code is about the sensor's heater, the fault is usually electrical.
Read the code and keep the report: with an ECO-LITE in the OBD socket you see it on your phone or computer, with the data captured when the fault happened.
Look for anything obvious: a loose connector, a disconnected hose, a fuel cap not closed properly or a low fluid level. Do not take apart anything you do not know.
Clear the code only after writing it down or after the repair. Clearing turns the light off, but it also deletes the freeze-frame data and the readiness monitors used at the inspection.
Drive normally for a few days and read the codes again. If the code comes back, the fault is still there: book the workshop and bring the report.
Read your car's fault codes on your phone
With an ECO-LITE in the OBD socket you see the codes in your account, with the data captured when the fault happened, and your workshop can check them remotely, always with your permission.
Related codes
- P0037HO2S heater (bank 1, sensor 2), control circuit: signal low
- P0038HO2S heater (bank 1, sensor 2), control circuit: signal high
- P0040O2 sensor signals swapped (bank 1 sensor 1 / bank 2 sensor 1)
- P0041O2 sensor signals swapped (bank 1 sensor 2 / bank 2 sensor 2)
- P0042HO2S heater (bank 1, sensor 3), control circuit: malfunction
- P0044HO2S heater (bank 1, sensor 3), control circuit: signal high
P00xx codes: fuel and air metering and auxiliary emission controls
In the glossary
Read more: Remote OBD diagnostics: what it is, how it works and what it can't do