What does P0042 fault code mean?
P0042 fault code, applicable to all car manufacturers, means “HO2S Heater Control Circuit (Bank 1, Sensor 3)“.
Background Information: The oxygen sensor’s function is to measure the oxygen content in the engine exhaust to correct the fuel injection quantity, thereby achieving the optimal air-fuel ratio for the engine. In OBD fault codes, you will often see the oxygen sensor number specified. Bank 1 refers to the bank containing cylinder 1, and the remaining bank is Bank 2. Regardless of the bank, the first sensor always refers to the upstream oxygen sensor (before the catalytic converter), and the second sensor always refers to the downstream oxygen sensor (after the catalytic converter). The Electronic Control Unit (ECU) maintains the oxygen sensor temperature at 780°C by controlling the on/off state of the oxygen sensor heater. If the oxygen sensor fails to reach the required temperature within the set time, or if the ECU cannot maintain the set temperature, this fault code will appear.
Symptoms of P0042 Error Code:
- Engine malfunction light illuminates
- Increased fuel consumption
- Poor cold start
- Unstable engine idle
- Increased exhaust emissions
Important! While the vehicle may continue to run, delaying repairs can lead to increased fuel consumption and damage to the catalytic converter.
The main causes of the P0042 error code:
- Damaged or corroded sensor wiring
- Oxygen sensor heater malfunction
- Burned heater circuit fuse
- Engine control unit problem (rare)
How to diagnose the P0042 error code?
Step 1: Use an OBD2 scanner to read the error and confirm the presence of P0042.
Step 2: Visually inspect the wiring and connectors of the No.3 oxygen sensor (Group 1).
Step 3: Check the integrity of the fuses and heating relay.
Step 4: Measure the resistance of the sensor heating element.
Step 5: Check the signal on the control line with a multimeter.
Tools needed: OBD2 scanner, multimeter, wrench and screwdriver set, contact cleaner, and electrical tape.
How to resolve the P0042 error code? (Solutions to the Problem)
Simple Troubleshooting
- Clean the sensor and connector contacts.
- Replace the blown fuse.
- Restart after fixing the error and check if the code reappears.
In-depth Diagnosis and Repair
- Replace Oxygen Sensor No. 3
- Repair or replace damaged wiring
- Check and replace the heater relay
- Test ECM output (as a last resort)
| Symptoms | Possible Solutions |
|---|---|
| Check engine stability | Check and replace the oxygen sensor |
| High fuel consumption | Diagnose and replace the HO2S heater |
| Poor cold start | Check the heating element and wiring |
P0042 Error Code FAQ:
Do you drive with error code P0042?
Yes, but not recommended. Error P0042 can affect engine performance and increase fuel consumption, and damage the catalytic converter over time.
How serious is the P0042 error?
This error is considered moderately serious. While it won’t immediately cause engine failure, ignoring it can lead to decreased environmental performance and fuel efficiency.
Can you reset error P0042 without fixing the problem?
Yes, it can be reset with an OBD2 scanner or by temporarily disabling the battery. However, if the cause of the malfunction is not resolved, the error will reappear.
Will error P0042 reappear after repair?
Yes, if the cause is not completely eliminated or low-quality spare parts were used. Repeated breakage or corrosion of the connectors is also possible.
Error Code P0042 in Different Vehicles
- Toyota’s P0042：In Toyota models, the error is often related to wear and tear on the λ sensor after more than 120,000 kilometers.
- BMW’s P0042：In BMW models, wiring breaks are common in the exhaust manifold area, especially in turbocharged models. Checking the integrity of the wire insulation is very important.
- Volkswagen’s P0042：Volkswagen’s HO2S heating element itself often fails. It is recommended to use the original sensor when replacing it.
- Ford’s P0042：Ford may have problems with fuses and relays, especially in older Focus and Escape models. Checking the circuit is necessary.