P0135: O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

written by Edmunds.com^{This story was created with generative AI and was reviewed and fact-checked by our staff of editors and experts.}
edited by Carrie Kim^{Creative Services Project Manager
Carrie Kim has been writing about cars for well over a decade. No matter if she's cruising with the family or chasing down her next breakfast burrito, she's (not so) silently judging car infotainment systems, interior color palettes, and dashboard finishes all along the way. She's a big fan of massaging seats, adaptive cruise control and wireless CarPlay. Over the years, she's particularly enjoyed helping parents find their own unique family wagons.}
11/15/2024
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Understanding P0135

The P0135 error code means "Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)." This code is triggered when the engine control module detects a problem with the heater circuit in the upstream oxygen sensor on Bank 1. This heater helps the oxygen sensor reach optimal operating temperature faster, ensuring more accurate air-fuel mixture readings in cold starts.

The importance of addressing P0135

The oxygen sensor heater malfunction affects the vehicle’s ability to regulate the air-fuel ratio accurately, especially during cold starts. Without a properly functioning oxygen sensor heater, the engine may run rich initially, which can reduce fuel efficiency, increase emissions, and eventually damage the catalytic converter. A persistent P0135 issue may lead to more severe and costly repairs.

Can I safely drive my car with this error code?

Yes, you can drive with the P0135 code, but it’s best to address this issue promptly. The malfunction may cause increased fuel consumption, higher emissions, and, if left unresolved, can lead to damage to other emission-related components.

Common cymptoms of P0135

Check engine light is on
Reduced fuel efficiency
Rough idling or poor performance, especially during cold starts
Increased exhaust emissions
Failed emissions test

Diagnosing P0135

To diagnose the P0135 code, technicians typically follow these steps:

Scan for codes: Use an OBD-II scanner to confirm the P0135 code and check for any other codes that might relate to the oxygen sensor or heater circuit.
Visual inspection: Inspect the wiring and connectors for the Bank 1, Sensor 1 oxygen sensor for damage or corrosion.
Check sensor resistance: Use a multimeter to measure the resistance of the oxygen sensor heater circuit; compare to manufacturer specifications.
Test voltage supply: Verify there's a proper voltage supply to the oxygen sensor’s heater circuit to rule out electrical issues with the engine control module or wiring.

Repairing P0135

Repairs for the P0135 code generally include the following steps:

Replace oxygen sensor: If testing reveals that the Bank 1, Sensor 1 oxygen sensor heater has failed, replace the sensor.
Repair wiring or connectors: If damaged wiring or connectors are found, repair or replace them to ensure proper circuit connectivity.
Clear code and test: Clear the code with an OBD-II scanner. Then start the vehicle and test to verify the code does not return and the heater circuit functions correctly.