What Does P015B Mean?
The O2 sensor on Bank 1, Sensor 1 (upstream, pre-catalytic converter) is exhibiting a delayed response when transitioning from a lean exhaust condition to a rich condition. The PCM has measured the specific delay time from when the exhaust goes rich to when the sensor voltage rises above the rich threshold, and it exceeds the calibrated limit. This primary fuel control sensor's delayed response affects fuel mixture accuracy during acceleration and load changes. Fuel economy may suffer.
Common Causes
40%
Degraded O2 sensor with increased response delay on the lean-to-rich transition
20%
Oil or coolant contamination on the sensor element slowing chemical reactions
20%
Exhaust leak on Bank 1 allowing air intrusion that delays the rich signal
10%
Wiring or connector degradation in the sensor signal circuit
10%
Vacuum leak on Bank 1 intake causing a lean bias that masks the rich transition
Diagnostic Steps
1
Monitor Bank 1 Sensor 1 voltage during a snap throttle enrichment — the sensor should rise above 0.7V within 100-150ms of throttle snap; a delayed sensor will take 300ms+ to register the rich condition.
2
Graph the sensor waveform alongside injector pulse width — the sensor voltage rise should closely follow the enrichment command with minimal lag.
3
Check Bank 1 STFT during a steady-state cruise and during acceleration — STFT swinging significantly positive during acceleration confirms the delayed rich response.
4
Check for vacuum leaks on Bank 1 using a smoke machine — unmetered air can cause a lean condition that delays the sensor's ability to detect enrichment.
5
Measure the O2 sensor heater resistance and verify the sensor is at full operating temperature (heater current 0.5-2.0A) — a partially heated sensor will respond more slowly.
Estimated Repair Cost
$100 - $400
Parts + labor, varies by vehicle and location
The O2 sensor on Bank 1, Sensor 1 (upstream, pre-catalytic converter) is exhibiting a delayed response when transitioning from a lean exhaust condition to a rich condition. The PCM has measured the specific delay time from when the exhaust goes rich to when the sensor voltage rises above the rich th...
The most common cause of P015B (O2 Sensor Delayed Response - Lean to Rich (Bank 1 Sensor 1)) is: Degraded O2 sensor with increased response delay on the lean-to-rich transition
Typical repair costs for P015B range from $100 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Drive with awareness. The delayed lean-to-rich response on this primary fuel control sensor means the engine may run momentarily lean during acceleration events, which can cause misfires and stress the catalytic converter. Repair in a timely manner.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P015B to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel System / Emissions
Difficulty
Type
Generic (SAE)
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