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P0138 on Volkswagen: Causes, Symptoms and Fix Cost

Quick Answer

Safe to drive (short-term)

P0138 on a Volkswagen 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 Volkswagen 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.

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What does P0138 mean on a Volkswagen?

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

Volkswagen Golf

2005-2024

On EA888 TSI engines a leaking injector can cause a real rich condition that triggers P0138, so check fuel trims before replacing the sensor. Oil consumption can also contaminate the sensor and shift its baseline reading. TDI models rarely throw P0138 because of their different exhaust sensor arrangement.

What causes P0138 on a Volkswagen?

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

  • EA888 leaking injector causing a real rich condition

    : Volkswagen Golf

  • Oil consumption contaminating sensor element

    : Volkswagen Golf

How to diagnose P0138 on a Volkswagen 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 Volkswagen? (EUR)

Estimated repair costs for P0138 in EUR, compiled across makes. Expect Volkswagen 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 Volkswagen

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