P0030 — HO2S Heater Control Circuit (Bank 1 Sensor 1)
P0030 means the heater circuit in the front oxygen sensor is not working. The sensor itself may be fine, but without the heater it cannot reach operating temperature quickly, which causes cold-start emissions problems.
The engine runs normally once warm, but cold starts may have rough idle, poor fuel economy, and increased emissions until the sensor heats up from exhaust gas alone.
What P0030 means
Modern oxygen sensors contain an internal heater element that brings the sensor to operating temperature within seconds of starting. The module controls this heater and monitors the current draw. P0030 sets when the current is outside the expected range — either open circuit, shorted to ground, or shorted to power. Without the heater, the sensor relies on exhaust heat alone, which means the engine runs in open-loop fuel control for much longer after a cold start.
| System | Emission control |
|---|
Symptoms you may notice
What causes P0030
Oxygen sensor heater element has failed
The internal heater wire breaks or burns out, which is the most common cause on sensors past 100,000 km.
Wiring or connector to the sensor is damaged
Chafed wires or corroded connector pins can interrupt power to the heater element. The harness near the exhaust manifold is a common failure point.
Blown fuse for the oxygen sensor heater circuit
A blown fuse interrupts power to the heater. Check the fuse before replacing the sensor — a shorted sensor may have caused the fuse to blow, and a new sensor with the same fault will blow it again.
How to diagnose it
Check the oxygen sensor heater fuse
Locate and inspect the fuse for the oxygen sensor heater circuit. If blown, check the sensor and wiring for a short before replacing the fuse.
Measure heater resistance at the sensor connector
Disconnect the sensor and measure resistance across the heater terminals. Typical specification is 4-40 ohms depending on the sensor.
Check for power at the connector
With the ignition on, check for battery voltage at the heater power feed wire at the sensor connector.
Related codes
Common questions
Can I drive with P0030?
Yes, the engine will run normally once warm. You will notice slightly worse fuel economy on cold starts and it will fail an emissions test in most jurisdictions.
Do I need to replace the whole sensor?
Usually yes — the heater is built into the sensor and cannot be replaced separately. However, check the fuse and wiring first, as a wiring fault can mimic a failed heater.
Last verified 2026-07-27 · Sources: SAE J2012 — Diagnostic Trouble Code Definitions and Failure Type Byte (SAE International)
This information is for general guidance and is not a substitute for professional diagnosis. Cost figures are estimates, not quotes.