O2 Sensor Heater Circuit (Bank 1 Sensor 1)

What it means

The upstream oxygen sensor has a built-in electric heater that brings it to working temperature quickly after start-up. The engine computer has found the heater current or warm-up time on bank 1 to be abnormal, so the sensor starts working late after a cold start and the computer relies on estimated fuel control for longer.

Related codes: P0030P0031P0032P0134P0141

Symptoms4

• Check engine light on.
• Slightly higher fuel use, especially on short trips.
• Higher emissions after a cold start.
• A sensor no-activity code such as P0134 may appear with it.

Possible causes5

• Burned-out heater element inside the sensor (most common).
• Blown fuse feeding the heater.
• Wiring or connector damaged by exhaust heat.
• Corroded connector terminals.
• Fault in the heater control circuit inside the engine computer (rare).

How to diagnose5

1. Check the oxygen sensor heater fuse per the owner's manual.
2. Unplug the sensor and measure heater resistance across its terminals, comparing it with the manufacturer specification; an open reading means a burned-out heater.
3. Confirm supply voltage reaches the connector with the ignition on.
4. Check the control wire from the computer for an open or short.
5. Inspect the connector and wiring near the exhaust for melting.

How to fix4

1. Replace the fuse if blown, and find why it blew before finishing the job.
2. Repair the damaged wiring or connector.
3. Replace the upstream oxygen sensor if the heater is open; the heater is not sold separately.
4. Clear the codes, then start the engine from cold and confirm the code does not return.

A fuse or wiring repair keeps the cost low, while a burned-out heater means replacing the whole sensor, which takes the cost to the upper end.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions