P0042
Fix within 1-2 weeksThe heater circuit for the downstream oxygen sensor on Bank 1 is not working correctly.
Code P0042 means your downstream oxygen sensor's heater circuit on Bank 1 is not working right. Common causes: Bad O2 sensor (75%), wiring damage (20%). Drivability: Yes, safe to drive. Repair cost: $50-$200 DIY, $150-$500 professional.
Can I Drive With P0042?
Yes, safe to drive
No restrictions
Stop driving immediately if: No need to stop driving for this code unless other symptoms develop.
Symptoms of P0042
- 1Check Engine Light is on
- 2Slight decrease in fuel economy (often unnoticeable)
- 3Vehicle may fail an emissions test
Common Causes of P0042
Parts most likely causing this code, ranked by probability
The heater element inside the oxygen sensor has failed, preventing it from reaching operating temperature quickly or at all.
75% of P0042 cases are fixed by replacing this part
Damaged, corroded, or open wiring to the oxygen sensor's heater circuit prevents power or ground from reaching the sensor.
20% of P0042 cases are fixed by repairing or replacing wiring
A blown fuse in the oxygen sensor heater circuit cuts off power to the sensor's heating element.
4% of P0042 cases are fixed by replacing a fuse
A faulty PCM is not providing the correct voltage or ground signal to the oxygen sensor heater circuit.
1% of P0042 cases are fixed by replacing the PCM
Check These First (Before Buying Parts)
- Visually inspect the Bank 1 Sensor 3 oxygen sensor and its wiring for any obvious damage, frayed wires, or loose connections. Look for signs of rodent activity.
- Locate the fuse box (check your owner's manual) and inspect the fuse for the oxygen sensor heater circuit. Replace it if it's blown.
How to Diagnose P0042
- 1Visually inspect the Bank 1 Sensor 3 oxygen sensor and its wiring for damage, corrosion, or loose connections.
- 2Locate and check the fuse for the oxygen sensor heater circuit; replace if blown.
- 3Disconnect the oxygen sensor and test the resistance of the heater circuit terminals on the sensor itself using a multimeter (should be a low resistance, typically 2-10 ohms).
- 4With the ignition on, check for 12V power and ground at the oxygen sensor harness connector using a multimeter.
- 5If power and ground are present and the sensor's heater resistance is out of spec, replace the oxygen sensor.
P0042 on Popular Vehicles
Toyota Camry
2007-2024Downstream O2 sensor heater circuit failures are common on these models as sensors age. Wiring damage from road debris or rodents is also a known issue.
80% fixed by replacing O2 sensor
Honda Accord
2003-2024Similar to Toyota, the downstream O2 sensor is a frequent culprit for P0042. Check the connector for corrosion, especially in areas with high road salt use.
78% fixed by replacing O2 sensor
Ford F-150
2004-2024On F-150s, the O2 sensor wiring can be exposed and vulnerable to damage from off-road driving or road debris. Always inspect the wiring thoroughly before replacing the sensor.
70% fixed by replacing O2 sensor
Frequently Asked Questions
What does P0042 mean?
P0042 indicates that the heater circuit for the Bank 1 Sensor 3 oxygen sensor has a low electrical reading, meaning it's not drawing enough current to heat up properly.
Can I drive with P0042?
Yes, you can drive safely with a P0042 code. This code primarily affects emissions monitoring and will not cause immediate engine damage or drivability issues. However, you will fail an emissions test.
Will P0042 clear itself?
No, P0042 will not clear itself. The underlying electrical fault in the heater circuit requires diagnosis and repair. The Check Engine Light will remain on until the issue is resolved.
How do I fix P0042 myself?
Start by visually inspecting the oxygen sensor and its wiring. Check the relevant fuse. If those are good, test the resistance of the sensor's heater element and check for power and ground at the sensor connector. Most often, replacing the Bank 1 Sensor 3 oxygen sensor fixes this code.
How much does it cost to fix P0042?
A DIY fix for P0042 typically costs $50-$200 for a new oxygen sensor. If you take it to a shop, expect to pay $150-$500, which includes parts and labor.
P0042 keeps coming back - why?
If P0042 keeps returning after replacing the sensor, the problem is likely in the wiring harness (damaged wires, poor connection) or a persistent fuse issue. A faulty PCM is a rare but possible cause.
Will P0042 fail emissions/smog test?
Yes, P0042 will cause your vehicle to fail an emissions or smog test. The oxygen sensor's heater circuit is crucial for proper emissions monitoring, and a fault means the system is not ready.
What's the difference between P0042 and P013A?
P0042 specifically indicates a problem with the *heater circuit* of the Bank 1 Sensor 3 oxygen sensor. P013A indicates a *slow response* from the same sensor, meaning the sensor itself is not switching voltage quickly enough, which can be caused by a failing sensor or exhaust leaks, but not necessarily a heater circuit issue.
P0042 on Toyota Camry?
On Toyota Camry models, P0042 is a common code, often indicating a failed downstream oxygen sensor (Bank 1 Sensor 3). These sensors are wear items and typically fail around 100,000-150,000 miles. Always check the wiring for rodent damage as well.
Questions to Ask Your Mechanic
Did you check the resistance of the O2 sensor's heater element?
Good answer: Yes, I measured the resistance, and it was out of specification, indicating an internal heater failure in the sensor.
What did you find when checking for power and ground at the O2 sensor connector?
Good answer: I confirmed there is 12V power and a good ground signal at the connector, so the wiring to the sensor is intact.
Repair Cost Estimate
DIY Repair
Parts only
$50-$200
Shop Repair
Parts + labor
$150-$500
Save $100-$300 by doing it yourself
Difficulty
intermediate
Time
0.5-2 hours
Intermediate - requires basic electrical testing with a multimeter and specific tools like an O2 sensor socket, but is generally manageable for someone with moderate mechanical experience.
Cost of Waiting
Ignoring P0042 will cause your vehicle to fail emissions inspections. While it won't cause immediate engine damage, the Check Engine Light will remain on, and your fuel economy might slightly decrease over time. A $50-$200 sensor replacement now prevents a failed inspection and potential fines.
While You're In There...
If you need to remove any exhaust components to access the sensor, replacing old gaskets prevents exhaust leaks and ensures a proper seal.
Applying anti-seize to the new O2 sensor threads prevents it from seizing in the exhaust pipe, making future removal much easier.
Tools You'll Need
- OBD-II scan tool
- Multimeter
- O2 sensor socket (7/8 inch or 22mm)
- Ratchet and extensions
- Wire brush (for cleaning threads)
- Anti-seize compound
P0042 is a very common code, and it's not a critical issue that will leave you stranded. Most repairs are straightforward, often just replacing the oxygen sensor, and your vehicle will be back to normal.
- Family-owned since 1957
- 990,000+ happy customers
- Fast nationwide shipping
- Easy returns
Your Next Steps
Step 1: Perform a thorough visual inspection of the Bank 1 Sensor 3 oxygen sensor and its wiring. Look for any cuts, burns, or signs of rodent damage. Check the electrical connector for corrosion or bent pins.
Step 2: Check the fuse for the O2 sensor heater circuit. Consult your vehicle's owner's manual for the exact fuse location and rating. Replace any blown fuses.
Step 3: If the fuse and wiring appear good, disconnect the sensor and use a multimeter to test the resistance of the heater element within the sensor itself. Also, check for 12V power and ground at the vehicle's wiring harness connector for the sensor. If the sensor's heater resistance is out of spec, or if power/ground is missing, you've found your problem.