Powertrain, generic · Fuel and air metering

P015B O2 Sensor Delayed Response - Lean to Rich Bank 1 Sensor 1

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

The upstream oxygen sensor (sensor 1, before the catalytic converter) is the main control sensor for the air-fuel mixture. 'Delayed response' means the sensor starts reacting too late, or does not reach the target level at all, after the mixture has changed. This code covers the lean-to-rich direction, tested when fuel returns or the control module briefly enriches the mixture. GM measures the upstream switching sensor's delay while the mixture is enriched for the downstream tests and fails a filtered delay above about 0.58 s (fallback 1.9 s) after one trip; the test needs the rich-to-lean counterpart P015A completed first. CARB requires separate detection of slow and delayed faults in each direction (phased in from 2009 for downstream and 2011 for upstream sensors).

Likely causes

Upstream oxygen sensor aged or poisoned (silicone, oil, coolant, soot)
Exhaust leak ahead of the sensor (manifold, flange)
Mixture fault: intake air leak, injectors, fuel pressure, air flow sensor
Sensor heater weak, sensor too cold
Connector, wiring or control module software

Symptoms

  • Check engine light on
  • Slightly higher consumption or rough idle possible
  • Higher emissions, possible emissions test failure
  • Often no noticeable symptoms

Repair estimate

DifficultyEasyDIY possible
Parts and labour€80–300
Time0.5–1.5 h

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

Parts involved

oxygen sensor bank1 sensor1exhaust systemoxygen sensor wiring

Related codes

P015AP014DP015DP0133P2A00P0131

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