P0135
Low SeverityO2 Sensor Heater Circuit (Bank 1, Sensor 1)
Emissions System
P0135 — Instant Answer
O2 Sensor Heater Circuit (Bank 1, Sensor 1)
Severity: LOW SEVERITY
Meaning: The heater in the upstream O2 sensor on bank 1 is not working properly. The heater brings the sensor to operating temperature quickly.
Safe to drive? Usually yes with caution, but confirm root cause before long trips.
Estimated repair cost: $30 - $100
Most common causes:
- 1. Failed O2 sensor heater (35-45% of cases)
- 2. Blown O2 heater fuse (10-25% of cases)
- 3. Wiring issue (10-25% of cases)
- 4. Corroded connector (10-25% of cases)
Symptoms
- ⚠️Check engine light
- ⚠️Slow warm-up fuel trim
- ⚠️Slightly increased emissions
- ⚠️Failed emissions test
Related Symptoms
Common Causes
How to Diagnose P0135
- 1Check O2 heater fuse
- 2Measure heater resistance (2-30 ohms normal)
- 3Check power and ground at sensor
- 4Replace sensor if heater open
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Related Symptoms
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Related Codes
The oxygen sensor heater circuit on the upstream (pre-cat) sensor of bank 1 has a fault. The heater gets the O2 sensor to operating temperature quickly for proper fuel trim.
The heater in the downstream O2 sensor on bank 1 has failed.
Heater failure in the upstream O2 sensor on bank 2.
Frequently Asked Questions
- Can a heater fault affect the O2 sensor reading?
- Not directly, but the sensor will take longer to warm up. In cold weather, fuel economy suffers during warm-up.
- Do all O2 sensors have heaters?
- All modern vehicles (1996+) have heated O2 sensors. The heater ensures accurate readings from cold start.
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Author & Review
Written by AllOEMManuals Editorial Team. Reviewed by ASE-certified technicians and updated with factory-reference checks for fitment-sensitive steps.
This guide was drafted with AI assistance and reviewed for accuracy by a human editor.
Last updated: 2026-05-07