The Quick Answer above is the generic definition. What follows is what is documented for the Volkswagen models that log P0138, checked against manufacturer data and owner reports.
DTC/P0138·Volkswagen
P0138 on Volkswagen: Causes, Symptoms and Fix Cost
Quick Answer
Moderate SeveritySafe to drive (short-term)Volkswagen
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.
Repair cost on Volkswagen€65 - €650
Connect any standard Bluetooth OBD2 adapter 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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Volkswagen Golf
2005–2024On EA888 TSI engines, leaking injectors and HPFP wear are documented causes of real rich conditions that trigger P0138. Check fuel trims before replacing the sensor. Oil consumption can also contaminate the sensor and shift its baseline reading. TDI models rarely throw P0138, the diesel exhaust aftertreatment uses different sensors.
What causes P0138 on a Volkswagen?
Beyond the generic causes listed on the main P0138 page, these are the documented Volkswagen-specific patterns:
Volkswagen GolfEA888 leaking injector or HPFP wear causing real rich condition
Volkswagen GolfOil consumption contaminating sensor element
How to diagnose P0138 on a Volkswagen with OBD2
Follow these steps to pinpoint the root cause of P0138:
- Read freeze frame data and check for companion codes (P0172, P0175, P0420) that point to a real rich condition or converter problem
- 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
- Check long-term fuel trims. If LTFT is significantly negative (under -10%), the engine is genuinely running rich
- Inspect the Bank 1 Sensor 2 signal wire for shorts to voltage, especially near heat shields and the battery positive cable
- 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.
Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.
Related codes that often appear with P0138 on Volkswagen
These codes commonly cluster with P0138 on Volkswagen vehicles:
Looking for the full P0138 reference (all makes, full diagnosis flow, complete repair cost matrix)?
See the main P0138 guideSkanyx · Volkswagen
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