P0147 Code: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 3)

What the P0147 code means

The bank 1 sensor 3 oxygen sensor is the O2 sensor on bank 1 (the side of the engine that has cylinder 1), downstream, behind the second catalytic converter (sensor 3). The computer uses it to watch the second converter on vehicles that have two in series.

O2 sensors have a heater element so they reach their working temperature quickly, which is more than 300 °C (about 570 °F). The computer controls that heater and watches its current. The P0147 code means the heater circuit is open, shorted, or drawing current outside the expected range. Without the heater, the sensor takes a long time to start working and the vehicle puts out more emissions after startup.

Because this is a sensor behind the converter, a failure does not usually affect how the car drives. It does stop the computer from monitoring the converter, and you will not pass an emissions test until it is fixed. The diagnosis section below shows how to test the circuit.

P0147 code symptoms

• Check engine light on.
• Normally no driveability symptoms.
• Oxygen sensor or catalyst monitors stay incomplete, so the vehicle fails an emissions test.
• More emissions and higher fuel use during the first minutes after a cold start.
• Other codes for the same sensor or for catalytic converter efficiency may show up too.

Likely causes of the P0147 code

1. Open heater resistance. The most frequent cause.
2. Blown heater fuse, which often feeds several sensors at once.
3. Burned connector or wire from the heat of the exhaust.
4. Heater relay (on some vehicles).
5. Control circuit in the computer. Uncommon.

How to diagnose the P0147 code step by step

1. Read the sensor live data with the engine warm. A healthy upstream sensor swings between 0.1 and 0.9 V several times a second. A healthy downstream sensor stays nearly steady between 0.5 and 0.8 V.
2. Look for exhaust leaks between the engine and the sensor. With the engine cold, listen for puffing or ticking, and hold a hand near the joints and gaskets (without touching them).
3. Inspect the wiring near the exhaust and the connector for oil, melted insulation or corroded pins.
4. Measure the heater resistance across the two wires of the same color (usually white or black). A rough guide is 2 to 20 ohms depending on the sensor type. Infinite resistance means an open heater.
5. Check for 12 V at the heater supply with the key on, and check the fuse.
6. Check continuity of the signal and ground wires all the way to the computer.

How to fix the P0147 code

• Repair exhaust leaks before you replace the sensor.
• Repair burned wiring and secure it away from the exhaust.
• If the sensor is contaminated, find and fix the source (oil, coolant, rich mixture) before you install a new one.
• Replace the sensor with one of the correct specification (type, number of wires and wire length). Since the heater is built into the sensor, you replace the whole sensor if the heater resistance is open.
• Use anti-seize on the threads only, never on the tip of the sensor.
• Clear the codes, drive a full cycle and confirm the sensor monitor reaches ready status. If the P0147 code returns, retest the heater circuit before you buy another part.

Technical reference data

• Conventional zirconia sensor: 0.1 V (lean) to 0.9 V (rich).
• Bias voltage with no activity: about 0.45 V.
• Typical heater resistance: 2 to 20 ohms.
• Operating temperature: more than 300 °C (about 570 °F).
• Common thread: M18 x 1.5; typical torque 40 to 50 N·m (about 30 to 37 lb-ft).
• These are reference values only. Check the specifications for your engine.

Brand-specific notes

On four-cylinder inline engines there is only bank 1, so bank 2 codes should never show up. The P0147 code is a bank 1 code and can appear on any engine that has a third oxygen sensor.

P0147 on Toyota and Lexus

On Toyota and Lexus the sensor 1 position is usually a wide-band (air-fuel ratio) sensor, and its equivalent codes are P2195 to P2199 and P2238 to P2243.

P0147 on GM, Toyota and Volkswagen

Sensor 3 positions are common on some GM, Toyota and Volkswagen vehicles that have two catalytic converters in series.

Frequently asked questions about P0147