P0135 indicates a problem with the heated oxygen sensor’s heater circuit, typically the upstream sensor on Bank 1 (Bank 1 Sensor 1). The fix usually involves checking the sensor, wiring, fuses, and replacing the sensor if needed.
What P0135 Means
The P0135 code points to a malfunction in the O2 sensor heater circuit for the upstream oxygen sensor on Bank 1. The heater helps the sensor reach its operating temperature quickly so its readings are accurate. When the heater circuit is faulty, the engine computer may rely on colder, less accurate readings, which can trigger the Check Engine Light and affect fuel trim and emissions performance.
Causes of P0135
The following common causes can lead to a P0135 diagnostic trouble code. Inspect these areas first and proceed to testing if the visual check looks good.
- Blown fuse or relay protecting the O2 sensor heater circuit
- Faulty upstream O2 sensor (Bank 1 Sensor 1)
- Short to ground or short to power within the heater circuit
- Moisture intrusion, contamination, or corrosion in the sensor connector
- PCM or control logic issue (less common, but possible)
The list above covers the most frequent causes. If you rule out obvious wiring issues and fuses, the sensor itself is often the culprit.
Diagnosis and Repair Steps
The following steps guide you through a practical, vehicle-safe approach to diagnosing and addressing P0135. They focus on safety, verification, and targeted repairs. If you’re not comfortable performing any step, seek a professional technician.
The steps below outline a structured diagnostic flow from quick checks to definitive tests.
- Verify the fault with a scan tool and note any related codes or live data for Bank 1 Sensor 1 and the heater circuit. Check for other O2 sensor codes that might indicate a broader wiring issue.
- Inspect the O2 sensor and harness visually. Look for damaged insulation, bent pins, corroded connectors, oil or-water intrusion, and secure connections. Re-seat or replace damaged connectors as needed.
- Check the relevant fuse(s) and relays that protect the O2 sensor heater circuit. Replace a blown fuse or faulty relay with an OEM-spec part and retest.
- Test the heater circuit resistance of Bank 1 Sensor 1 with a multimeter according to the vehicle’s service manual. Compare measured resistance to the OEM specification. An open circuit (infinite resistance) or a resistance far outside spec usually means a faulty sensor.
- Inspect the wiring between the sensor and PCM for continuity and absence of shorts to ground or power. Repair or replace damaged wire runs and ensure proper insulation and routing away from heat sources or moving parts.
- If the heater circuit tests show the sensor is faulty or the heater cannot be supplied with 12V as commanded, replace the upstream O2 sensor (Bank 1 Sensor 1) with a new, quality OEM-equivalent sensor and connect all harnesses securely.
- Clear the codes with your scan tool and perform a road test or drive cycle to allow the PCM to monitor the new sensor and heater operation. Verify that P0135 does not return and that sensor readings warm up appropriately.
Note: Some vehicles require a specific drive cycle to re-learn after sensor replacement. Always consult the vehicle’s service manual for exact procedures and torque specifications for sensor installation.
If the code persists after replacing the sensor and confirming wiring and fuses are sound, a professional diagnostic may be needed to check the PCM logic or to diagnose a hidden fault in the engine management system.
Summary
P0135 signals a fault in the upstream O2 sensor heater circuit (Bank 1 Sensor 1). Start with a visual inspection, verify fuses and wiring, and test the sensor’s heater resistance. Replace the sensor if needed, then clear codes and perform a proper drive cycle to verify a permanent fix. If in doubt, consult a qualified technician to avoid misdiagnosis or improper repairs.
How do I fix the engine code 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.
How much does it cost to replace a Bank 1 O2 sensor?
The average cost for an O2 sensor replacement is between $362 and $412. This figure includes labor expenses between $63 and $79, while parts range from $300 to $333.
How much does it cost to fix P0135?
Fixing P0135 is usually an inexpensive repair. Depending on your vehicle, a new oxygen sensor costs between $20 and $200. Labor can add another $50 to $200 if you go to a mechanic.
Where is the O2 sensor heater circuit bank 1 sensor 1?
The 1st sensor is located closest to the engine and the last is located at the rear of the exhaust system. Some Diesel engines have a lot of exhaust temperature sensors and it can use Sensor 1 – 2 – 3 – 4 etc. In these cases = Sensor 1 is located nearest the engine and the last sensor in the read of the exhaust system.