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.

Likely causes

Symptoms

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

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, en.wikipedia.org, gsi.ext.gm.com.