O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
The P0135 code indicates a malfunction in the heater circuit of the oxygen sensor located before the catalytic converter on Bank 1 (engine side with cylinder #1). The heater element is essential for the sensor to reach operating temperature quickly, especially during cold starts. When the powertrain control module (PCM) detects an open, short, or excessive resistance in the heater circuit, it triggers this code. Common causes include a blown fuse, damaged wiring, or a faulty oxygen sensor.
1. Most Common Causes
- Failed internal heating element in the oxygen sensor (Bank 1, Sensor 1)
- Short to ground in the heater circuit wiring
- Short to battery voltage in the heater circuit wiring
- Open circuit or high resistance in the sensor wiring or connectors
- Blown heater circuit fuse (depending on vehicle design)
- Corroded, oxidized, or bent/disconnected pins at the sensor connector
- Failed heater driver or control circuit inside the PCM
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Increased fuel consumption
- Failed emissions test
- Rough idle or hesitation during cold start
- Possible black smoke from exhaust (rich condition)
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0135 and check for other codes.
Step 2: Visually inspect the O2 sensor wiring and connector for damage, corrosion, or loose connections.
Step 3: Check the O2 sensor heater fuse with a multimeter; replace if blown.
Step 4: Measure resistance across the heater circuit pins of the sensor; compare to manufacturer specs (typically 2-10 ohms).
Step 5: If resistance is out of range, replace the oxygen sensor.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but it may cause poor fuel economy and increased emissions. Prolonged driving can damage the catalytic converter.
How much does it cost to fix?▼
Typically $50-$150 for a DIY replacement of the oxygen sensor. Professional repair including diagnosis and labor may cost $150-$300.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.