Cause
Exhaust leak upstream of the sensor
A blowing joint, cracked manifold or corroded pipe ahead of the sensor, letting air into the exhaust stream before the sensor measures it. The sensor is then reading a diluted sample and reporting it faithfully — which is why replacing it changes nothing.
It matters because exhaust pulses are not a steady flow. Between pulses the pressure at a leak can drop below atmospheric and draw fresh air in, so a leak admits oxygen even though the exhaust is nominally under pressure. Oxygen, NOx, temperature and soot sensors are all misled by it, each in its own direction.
The audible clue is a ticking or blowing noise that is loudest from cold and quietens as the metal expands and closes the gap — which is exactly why it is so often missed on a warm car on a ramp. On an untouched vehicle setting a sensor correlation or sample-error code, this is the first thing to rule out.
Typically a moderate job.
Codes this can cause (21)
Codes where this is a likely explanation first, rather than merely a possible one.
- P013E O2 Sensor Delayed Response - Rich to Lean Bank 1 Sensor 2 Likely for this code Moderate
- P013F O2 Sensor Delayed Response - Lean to Rich Bank 1 Sensor 2 Likely for this code Moderate
- P014A O2 Sensor Delayed Response - Rich to Lean Bank 2 Sensor 2 Likely for this code Moderate
- P014B O2 Sensor Delayed Response - Lean to Rich Bank 2 Sensor 2 Likely for this code Moderate
- P015A O2 Sensor Delayed Response - Rich to Lean Bank 1 Sensor 1 Likely for this code Moderate
- P015C O2 Sensor Delayed Response - Rich to Lean Bank 2 Sensor 1 Likely for this code Moderate
- P015D O2 Sensor Delayed Response - Lean to Rich Bank 2 Sensor 1 Likely for this code Moderate
- P225D NOx Sensor Performance - Signal Biased/Stuck Low Bank 1 Sensor 1 Likely for this code High
- P229F NOx Sensor Circuit Range/Performance Bank 1 Sensor 2 Likely for this code Moderate
- P24DA Particulate Matter Sensor Exhaust Sample Error Bank 1 Likely for this code Moderate
- P013A O2 Sensor Slow Response - Rich to Lean Bank 1 Sensor 2 Moderate
- P016C Closed Loop Air/Fuel Ratio Control At Limit - System Too Lean Moderate
- P050E Cold Start Engine Exhaust Temperature Too Low Moderate
- P20EE SCR NOx Catalyst Efficiency Below Threshold Bank 1 Catalyst 1 High
- P225C NOx Sensor Performance - Signal Biased/Stuck High Bank 1 Sensor 1 Moderate
- P242B Exhaust Gas Temperature Sensor Circuit Range/Performance Bank 1 Sensor 3 Moderate
- P244A Particulate Filter Differential Pressure Too Low Bank 1 Moderate
- P245F Particulate Filter Pressure Sensor B Circuit Range/Performance Moderate
- P249E Closed Loop Reductant Injection Control At Limit - Flow Too High Moderate
- P24AF Particulate Matter Sensor Circuit Range/Performance Moderate
- P24C2 Exhaust Gas Temperature Measurement System - Multiple Sensor Correlation Bank 1 Moderate
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