P0135 means O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1). The heater inside the upstream bank 1 oxygen sensor is not working or its circuit is faulty, so the sensor takes longer to start working after a cold start. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0135 means
Oxygen sensors measure the oxygen left in the exhaust. Sensor 1 sits before the catalytic converter and is used for fuel control; sensor 2 sits after it and mainly monitors the converter. Most sensors have a heater so they start working soon after a cold start. A traditional zirconia sensor switches between about 0.1 volt (lean) and 0.9 volt (rich); many newer upstream sensors are wide-band air-fuel sensors that report differently, so check which type your engine uses.
P0135 symptoms
- Check engine light
- Slightly worse fuel economy after cold starts
- Usually no drivability change
Common causes of P0135
- Failed heater element inside the sensor (most common)
- Blown heater fuse
- Damaged wiring or connector
- Heater control fault in the engine computer
How to diagnose P0135
- Check the oxygen sensor heater fuse
- Measure heater resistance at the sensor connector
- Check for battery voltage on the heater supply wire with the key on
Can you drive with P0135?
Yes; it is not urgent, but repair it so fuel control starts promptly.
P0135 tips
Heater codes are among the most common oxygen sensor faults. Heater resistance is usually a few ohms to a few tens of ohms depending on the sensor; an open reading confirms a failed heater. Check the fuse first, because one blown fuse can set heater codes for several sensors.
Will P0135 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0135 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0141 | O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2) |
| P0134 | O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1) |
| P0133 | O2 Sensor Circuit Slow Response (Bank 1 Sensor 1) |
Guides that help
When it is more than a sensor
Oxygen sensor codes are fixed with a sensor, wiring, a fuse or an exhaust leak repair. An engine burning oil or coolant contaminates sensors quickly; if new sensors keep failing, check for blue or white exhaust smoke and a head gasket leak, and compare engines by code on our engines page if the engine is worn out.
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