Powertrain, generic · Fuel and air metering

P01F7 O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 4

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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. P01F7 means the sensor stays rich: when the module leans the mixture or cuts fuel on overrun, the signal does not drop into the lean range. CARB names exactly this rich-to-lean transition during fuel cut-off as the minimum check for downstream sensors; GM tests sensor 2 this way as a two-trip fault. Usual causes are a sooted or oil-fouled sensor or a signal wire shorted to the heater supply.

Likely causes

Sensor sooted, oil-fouled or aged
Signal wire shorted to voltage (e.g. heater supply)
Mixture genuinely rich (leaking injector, coolant or oil burning)

Symptoms

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

Repair estimate

DifficultyEasyDIY possible
Parts and labour€60–300
Time0.5–1.5 h

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

Parts involved

oxygen sensor bank1 sensor4oxygen sensor wiringcatalytic converter

Related codes

P01F6P01F5P2271P2273P0420

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