P01F5 O2 Sensor Circuit No Activity Detected Bank 1 Sensor 4

Sensor 4 on bank 1 is a fourth oxygen sensor, downstream of a further converter. No manufacturer or vehicle using sensor 4 codes could be identified (GM and Ford documents stop at sensor 3); the description follows CARB's requirements for downstream sensors and GM's checks on sensor 2. P01F5 means that with a warm engine and heated sensor the signal does not switch between rich and lean but stays in the middle or at the bias voltage the module applies. For sensor 2, GM detects this when the signal stays above 1.7 V of a 1.9 V bias, a two-trip fault. Usual causes are an open signal or ground wire or a dead sensor.

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, gsi.ext.gm.com, en.wikipedia.org.