P0135 code: O2 sensor heater circuit (bank 1 sensor 1)

What P0135 means

P0135 is the generic SAE code for O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1). An oxygen sensor only works well when it is hot. To get it to operating temperature quickly after a cold start, the sensor has a built-in electric heater. The PCM controls or monitors that heater and checks its current or resistance.

If the heater circuit is open, shorted or out of the expected range, the PCM sets P0135. Bank 1 is the side of the engine with cylinder 1. Sensor 1 is the upstream sensor, before the catalytic converter. On many vehicles this is the sensor the PCM uses for fuel control, so its heater matters most right after a cold start.

Symptoms of P0135

Because the exhaust heats the sensor once the engine is warm, many cars with P0135 drive normally. The O2 sensor monitor may also show as not ready, which can fail an inspection. See readiness monitors explained.

• Check engine light on
• Slightly worse fuel economy, especially on short trips
• Longer time before the engine goes into closed loop fuel control
• Higher emissions after a cold start; possible failed emissions test
• Often no drivability symptoms at all

Common causes of P0135

The heater element inside the sensor wears out over time, which makes it the most common cause. Still, check the fuse and wiring first, since they cost less and a blown fuse can point to a short you need to fix.

How to diagnose P0135

You need a scan tool and a basic multimeter. Pin layouts and resistance specs vary by vehicle, so use the service information for your car.

1. 1

   Read all codes and freeze frame. Note if P0141 (downstream heater) or other O2 codes are also set. Two heater codes at once often point to a shared fuse or power supply.

2. 2

   Check the fuse for the O2 sensor heaters.

3. 3

   Locate bank 1 sensor 1, upstream of the catalytic converter. Inspect the wiring along the exhaust and the connector.

4. 4

   Unplug the sensor and measure resistance across the two heater pins on the sensor side. An open reading (infinite resistance) means the heater is burned out.

5. 5

   With the key on, check for battery voltage at the heater power pin on the harness side. Check the ground or PCM control side as the wiring diagram describes.

6. 6

   Replace the failed part, clear the code, and check that the O2 sensor monitor completes after a drive cycle.

Note.Exhaust parts get very hot. Let the engine cool before you touch the sensor. If you lift the car, use jack stands on solid ground and never work under a car held only by a jack.

Find a scanner for O2 sensor data →

How to fix P0135

If the heater tests open, replace the upstream O2 sensor with the correct part for your engine. An O2 sensor socket and penetrating oil make removal easier; sensors can be tight after years of heat. Apply anti-seize only if the new sensor does not already have it, and keep it off the sensor tip. If the fuse or wiring was the problem, repair that and confirm the heater works. Then clear the code.

Can you drive with P0135?

Yes, in most cases. P0135 rarely affects how the engine runs once it is warm. The downsides are slightly higher emissions and fuel use after cold starts, an incomplete O2 monitor for inspection, and a check engine light that could hide a new code. Fix it when convenient. If the fuse keeps blowing, find the short soon. See can you drive with the check engine light on.

Related codes

P0141 is the same heater fault on bank 1 sensor 2, the downstream sensor. P0155 is the bank 2 sensor 1 heater. P0171 and P0172 are fuel mixture codes that involve the upstream sensor reading, and P0420 involves the downstream sensor. Use the code decoder to look up others.

Frequently asked questions

Do I always need a new O2 sensor for P0135? No. A failed heater element is the most common cause, but a blown fuse or damaged wiring can set the same code. Test before you buy.

Which sensor is bank 1 sensor 1? It is the upstream oxygen sensor, before the catalytic converter, on the side of the engine with cylinder 1. On an inline engine there is only one bank.

Can I clean an O2 sensor to fix P0135? No. The heater element is inside the sensor and cannot be repaired. If the heater is open, the sensor must be replaced.

Will P0135 make me fail emissions? It can. The check engine light and an incomplete O2 sensor monitor can both cause a failed or rejected inspection in many states. A good OBD2 scanner shows monitor status before you go.