P01F4: O2 Sensor Circuit Slow Response Bank 1 Sensor 4

Sensor 4 on bank 1 is a fourth oxygen sensor, behind a third converter or converter brick. The OBD standard provides for up to four sensors per bank, and the code standard defines sensor 4 for bank 1 only. No manufacturer or vehicle using these codes could be identified; the description rests on CARB's requirements for downstream oxygen sensors and the logic of sensors 2 and 3. A switching sensor delivers about 0.1–0.9 V. P01F4 means the sensor reacts too slowly to mixture changes; CARB requires at least a rich-to-lean response test of downstream sensors during fuel cut-off. Behind several converters the oxygen storage buffers the change, so limits are wide.

Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.

Symptoms

• Check engine light on (usually after two drive cycles)
• Catalyst monitor readiness possibly not set
• Usually no change in driving

Most likely causes

• Sensor aged or contaminated
• Exhaust leak ahead of the sensor
• Sensor heater weak

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the wiring and connector of the sensor indicated
2. Look for exhaust leaks
3. Check the signal in live data with the engine warm
4. Check the fuse and the heater resistance if the code mentions it
5. Replace the sensor if it has power and does not respond

Good to know

• Repair difficulty: easy
• It affects emissions.

What each character of P01F4 means

• P: Powertrain: engine and transmission
• 0: Generic code: same on every make
• 1: Air and fuel
• F4: Specific fault in that system

Frequently asked questions

Can I keep driving with code P01F4?

Yes, you can normally drive in moderation, but get it repaired soon: you will use more fuel and the catalytic converter can be damaged over time.

What causes code P01F4?

The most common causes are: sensor aged or contaminated; exhaust leak ahead of the sensor; sensor heater weak.

Related codes

• P01F1O2 Sensor Circuit Bank 1 Sensor 4
• P01F2O2 Sensor Circuit Low Voltage Bank 1 Sensor 4
• P01F3O2 Sensor Circuit High Voltage Bank 1 Sensor 4
• P0145O2 Sensor Circuit Slow Response Bank 1 Sensor 3
• P0139O2 Sensor Circuit Slow Response Bank 1 Sensor 2

Sources

• law.cornell.edu: 13 CCR 1968.2
• en.wikipedia.org: Oxygen sensor
• gsi.ext.gm.com: 18OBDG03A Engine Diagnostics

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.