The Quick Answer above is the generic definition. What follows is what is documented for the Audi models that log P0139, checked against manufacturer data and owner reports.
DTC/P0139·Audi
P0139 on Audi: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Audi
P0139 on a Audi means the downstream oxygen sensor on Bank 1 (post-catalyst, Sensor 2) is not switching between rich and lean readings quickly enough during the ECU's catalyst test. The downstream sensor should stay relatively flat under normal driving but must respond predictably during diagnostic sweeps. Slow response usually points to an aged sensor or a contaminated element.
Repair cost on Audi€45 - €310
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Audi A4
2006–2024The B7 and B8 A4 with 2.0 TFSI shares the EA888 oil consumption pattern. Carbon buildup on intake valves can also cause unstable combustion that the downstream sensor reads as slow response because the gas sample itself is inconsistent. Walnut blasting is recommended before sensor replacement on any TFSI over 80,000 km.
What causes P0139 on a Audi?
Beyond the generic causes listed on the main P0139 page, these are the documented Audi-specific patterns:
Audi A4EA888 oil consumption slowing sensor response
Audi A4Intake carbon buildup causing inconsistent combustion samples
How to diagnose P0139 on a Audi with OBD2
Follow these steps to pinpoint the root cause of P0139:
- Read freeze frame data and look for companion codes (P0420, P0136) that indicate a converter or sensor cluster issue
- Inspect the exhaust system between the catalytic converter and downstream sensor for leaks that could distort the gas sample
- Inspect the Bank 1 Sensor 2 connector and wiring for corrosion, heat damage, or partial open circuits
- Use a scan tool to graph downstream O2 voltage during a steady cruise and during deceleration fuel cut. A healthy sensor reacts within roughly 100 ms to the lean spike when fuel is cut
- Substitute a known-good sensor. Sensor response time is the only definitive test, so if the new sensor responds correctly, the original was aged out
How much does P0139 cost to fix on a Audi? (EUR)
Estimated repair costs for P0139 in EUR, compiled across makes. Expect Audi parts and labour towards the upper end of each range.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0139 on Audi
These codes commonly cluster with P0139 on Audi vehicles:
Looking for the full P0139 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0139 guideSkanyx · Audi
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