What causes fault code P015A?

• Most likely: Faulty or fouled Oxygen sensor (O2 sensor) • Likely: Exhaust leak upstream of or near the sensor • Possible: Damaged wiring or corrosion in the connector • Rare: Defective fuel pressure regulator causing unstable pressure

Powertrain (Engine & Gearbox)Standard EOBD

P015A - O2 Sensor Delayed Response - Lean to Rich (Bank 1 Sensor 1)

Q: What are the symptoms of fault code P015A?

• Check Engine Light (MIL) illuminated • Increased fuel consumption • Rough idling or hesitation during acceleration • Failed emissions test • Reduced engine performance

Q: How do you fix fault code P015A?

STEP 1: Visually inspect the exhaust system for leaks (cracks in manifold or loose bolts) as air intake mimics a lean condition. Inspect wiring and connectors for damage. STEP 2: Use a scan tool to monitor Live Data. Observe 'O2 Voltage Bank 1 Sensor 1'. During acceleration, voltage should rapidly transition from approx 0.1V to 0.9V. A slow 'lazy' transition confirms a faulty sensor. STEP 3: Check the heater circuit resistance. It should typically be between 2-20 Ohms. Verify the 5V reference voltage and ground integrity. STEP 4: Replace the Oxygen sensor on Bank 1, Sensor 1. Always use OEM-quality sensors as universal versions often lack the required response speed.

Last updated:1 February 2026

Related:O2-sensor (Bank 1, Sensor 1), Exhaust Manifold, ECU / Motorstyreenhet, Maf-sensor (Mass Air Flow)

System

Powertrain (Engine & Gearbox)

Related Fault Codes

P0100

Mass or Volume Air Flow A Circuit Malfunction

P0101

Mass or Volume Air Flow Circuit Range/Performance Problem

P0102

Mass Air Flow (MAF) Circuit Low Input

P0103

Mass or Volume Air Flow Circuit High Input

Technical Description

P015A indicates that the Engine Control Unit (ECU) has detected an abnormally slow response time from the upstream Oxygen (O2) sensor on Bank 1 during a transition from a lean to a rich air-fuel mixture. The ECU monitors the cycle rate of the sensor's voltage output. If the response time to switch from low voltage (lean) to high voltage (rich) exceeds the calibrated threshold (typically >100ms for specific voltage increments), the code is stored. This failure disrupts closed-loop fuel control and can force the engine into open-loop operation to prevent catalyst damage.

Possible Causes

Faulty or fouled Oxygen sensor (O2 sensor)

Exhaust leak upstream of or near the sensor

Damaged wiring or corrosion in the connector

Defective fuel pressure regulator causing unstable pressure

Symptoms

Check Engine Light (MIL) illuminated

Increased fuel consumption

Rough idling or hesitation during acceleration

Failed emissions test

Reduced engine performance

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P015A - O2 Sensor Delayed Response - Lean to Rich (Bank 1 Sensor 1)

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P015A - O2 Sensor Delayed Response - Lean to Rich (Bank 1 Sensor 1)

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