Skip to content
Skanyx

P0138 on Audi: Causes, Symptoms and Fix Cost

Quick Answer

Safe to drive (short-term)

P0138 on a Audi means the downstream oxygen sensor on Bank 1 (post-catalyst, Sensor 2) is reporting a voltage that is too high for too long, above roughly 1.0V. A healthy downstream sensor reads around 0.6-0.8V steady. Persistent high voltage typically indicates a rich exhaust condition, a short to voltage in the wiring, or a contaminated sensor.

Severity
Moderate · Emissions
Typical repair cost, all makes
€65-€650

Connect a standard OBD2 adapter (Bluetooth LE on iPhone) to your Audi and Skanyx tells you what P0138 means on that engine, whether it is safe to keep driving, and what the fix should cost. Free on iPhone and Android.

Get Skanyx free

What does P0138 mean on a Audi?

The Quick Answer above is the generic definition. What follows is the model-specific detail for the Audi models that log P0138.

Audi A4

2006-2024

On the B7 and B8 A4 2.0 TFSI (EA113 in the B7, EA888 in the B8), check fuel trims and injector condition before blaming the sensor, since a leaking injector causes a genuine rich condition. Wear of the high-pressure pump cam follower on the EA113 lowers fuel pressure rather than raising it, so it leans the mixture and is not a P0138 cause. The sensor runs roughly 70 to 220 euros depending on where you buy it.

Source: shopdap.com

Sources

  1. shopdap.com shopdap.com/blog/post/vw-audi-2-0t-fsi-cam-follower-and-camshaft-wear-problems.h

What causes P0138 on a Audi?

Beyond the generic causes listed on the main P0138 page, these are the patterns noted for Audi models:

  • Leaking injector causing a genuine rich condition

    : Audi A4

  • Oil consumption on the EA888 contaminating the sensor

    : Audi A4

How to diagnose P0138 on a Audi with OBD2

  1. Read freeze frame data and check for companion codes (P0172, P0175, P0420) that point to a real rich condition or converter problem
  2. Use a scan tool to view downstream sensor voltage. A reading stuck above 0.9V at idle indicates a rich condition or a faulty sensor
  3. Check long-term fuel trims. If LTFT is significantly negative (under -10%), the engine is genuinely running rich
  4. Inspect the Bank 1 Sensor 2 signal wire for shorts to voltage, especially near heat shields and the battery positive cable
  5. Substitute a known-good sensor. If high voltage persists, the issue is fuel mixture or wiring, not the sensor

How much does P0138 cost to fix on a Audi? (EUR)

Estimated repair costs for P0138 in EUR, compiled across makes. Expect Audi parts and labour towards the upper end of each range.

Repair Parts Cost Labor Cost Total Estimate DIY Difficulty
Replace downstream O2 sensor (Bank 1, Sensor 2) €40–€180 €50–€130 €90–€310 Moderate
Repair shorted O2 sensor wiring €5–€30 €60–€150 €65–€180 Moderate
Diagnose and fix rich condition (injector, fuel pressure) €30–€400 €80–€250 €110–€650 Professional

Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.

These codes are often seen alongside P0138 or point to related issues, on any make:

Looking for the full P0138 reference (all makes, full diagnosis flow, complete repair cost matrix)? See the main P0138 guide

Diagnose P0138 on your Audi

Get Skanyx free