P0042: HO2S Heater Control Circuit Bank 1 Sensor 3
Generic electrical fault in the heater control of the bank 1, sensor 3 oxygen sensor (typically a third sensor downstream of multi-stage cat or NOx trap).
What P0042 means
P0042 is a generic OBD-II powertrain code in the fuel & air group. In plain English: the computer found an electrical fault in that circuit: an open, short or bad connection, or a failed component. Bank 1 is the side of the engine with cylinder 1 (inline engines only have bank 1).
- Check engine light
- Usually on
- Emissions-related
- Yes — can fail inspection
- Limp mode possible
- Not typical
- Drive cycle to clear
- Required
Get it fixed
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Common causes
- 01Heater element openMost likely
- 02Heater wiring or connector faultPossible
Can I drive with P0042?
Usually yes, for a short time.
The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
Why we rate it moderate
- Turns on the check engine light
- Emissions-related: will usually fail an OBD inspection
- Needs a drive cycle to confirm a repair
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose P0042
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just P0042. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Check for related codes first
Look for P0062. Related codes often share a cause; a circuit or sensor code usually needs fixing before a performance code like this one.
- 3
Test the circuit
Inspect the wiring and connector at the oxygen sensor (bank 1, sensor 3) heater and heater wiring for damage, corrosion or chafing. With a multimeter, check supply voltage, ground and signal against the specifications in the service manual for your vehicle.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Heater element open; heater wiring or connector fault. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and complete a full drive cycle (cold start, idle, steady highway cruise, deceleration). The code is fixed when the related readiness monitor completes without it returning.
P0042 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Moderate
- Good DIY job?
- Yes, with a scan tool
Needs a scan tool and some experience with testing.
Parts and systems involved
- Oxygen sensor (Bank 1, sensor 3) heater
- Heater wiring
P0042 FAQ
What does P0042 mean?
P0042 means “HO2S Heater Control Circuit Bank 1 Sensor 3”. Generic electrical fault in the heater control of the bank 1, sensor 3 oxygen sensor (typically a third sensor downstream of multi-stage cat or NOx trap).
Is P0042 serious? Can I keep driving?
We rate P0042 as moderate severity. Usually yes, for a short time. The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
What causes P0042?
The most common causes, from most to least likely: Heater element open; Heater wiring or connector fault. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix P0042?
Typical labor is about $65–$250 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix P0042 myself?
DIY difficulty is moderate. Many owners can handle it with a scan tool, a multimeter and basic hand tools. Always confirm the cause before buying parts.
Will P0042 clear itself?
Once the fault is fixed, the check engine light usually goes off by itself after the system passes its self-test over several drive cycles. Clearing the code with a scan tool resets readiness monitors, so an inspection station may turn you away until a full drive cycle is completed.