P0042 Code: Meaning, Symptoms, Causes & Fix

Overview

Symptoms

• increased fuel use
• reduced performance
• rough operation in certain conditions

Common causes

• Disconnected or loose connector affecting ho2s heater control circuit (bank 1, sensor 3)
• Broken terminal inside harness
• Connector pin damage/corrosion or harness stress near related components

How to diagnose P0042

1. Confirm P0042 and capture freeze-frame data with a professional scan tool.
2. Inspect wiring, connectors, and grounds related to ho2s heater control circuit (bank 1, sensor 3) for obvious defects.
3. Use a continuity test from module pin to component to identify opens/high resistance.
4. Check for related DTCs to identify the root-cause chain before replacing parts.
5. After repair, clear codes and confirm readiness monitors complete without recurrence.

Severity of code P0042

Moderate: This code is moderate severity: the vehicle may still operate, but fault progression can increase repair cost over time.

Can you drive with P0042?

Most vehicles can be driven short-term with P0042, but postpone heavy load/highway driving until repaired.

If the warning lamp is flashing or drivability/safety is affected, avoid driving and diagnose immediately.

How to fix it (step-by-step)

1. Repair obvious wiring/connector faults first to prevent repeat parts replacement.
2. Address the root fault mode (open) in the ho2s heater control circuit (bank 1, sensor 3) circuit/system.
3. Apply the required relearn/adaptation procedure if specified by service information.
4. Road-test and verify P0042 remains cleared under the conditions that originally set the code.

Fix options

• Restore continuity and verify pin tension.
• Repair open circuit and secure connector lock.
• Clear DTCs and verify with live data and completed drive cycle.

Typical repair cost

$200-$900

Common mistakes when diagnosing P0042

• Replacing parts without verifying voltage, ground, and signal integrity first.
• Ignoring related stored/pending codes that indicate upstream faults.
• Skipping post-repair verification drive cycle and readiness checks.

P0042 in common vehicles

P0042 appears across makes such as Mazda, Subaru, Lexus, Jeep. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes P0042?

P0042 is commonly set by open faults affecting ho2s heater control circuit (bank 1, sensor 3).

How much does it cost to fix P0042?

For P0042, repair costs are typically $200-$900 depending on exact root cause, labor rates, and part quality.

Can I clear P0042 without repair?

You can clear P0042 temporarily, but the code usually returns until the underlying fault is corrected.

Helpful tools

• Estimate repair cost
• Decode your VIN
• Calculate fuel cost