P3370 — Lambda control exhaust bank 4, sensor 1, system too lean
Documented by: AUDI, SEAT, SKODA — the meaning can differ between manufacturers
P3370 points at oxygen sensor (sensor 1). The standard definition names the system involved; which part inside it has actually failed is what the checks below establish, cheapest first.
Common causes
The cause is almost always one of a few things. Here they are — P3370 rarely comes from anything outside this list:
- Sensor aged and slow to respond
- Heater element failed inside the sensor
- Wiring or connector fault at the sensor
- Exhaust leak near the sensor drawing in air
- Engine genuinely running rich or lean
Where to start
In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:
- Read the sensor's live trace — a lazy or flat signal identifies an aged sensor without removing anything
- Check for exhaust leaks upstream of the sensor
- Inspect the connector, which sits in a hot and exposed place and corrodes
- Measure the heater resistance against specification
- Replace the sensor once the exhaust and wiring are ruled out
That is what holds for P3370 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.
Why TorqFix for your car?
Above is what the code means and why it appears. TorqFix goes further — it gives you specific procedures, torque values, wiring diagrams and pinouts for your exact engine, not generic steps for every car. Real workshop data (127,000+ diagrams, 10,000+ procedures), interpreted by AI in your language.
Free with an account: 4 questions per day · drawings are Pro. Signing up takes twenty seconds and needs no card.
Code breakdown
🔧 Related repair procedures
- AUDI: Removing and installing front exhaust pipe (left-side) with catalytic converter - vehicles with multitronic gearbox 01J
- AUDI: Removing and installing starter catalytic converter (right-side)
- AUDI: Removing and installing front exhaust pipe (left-side) with starter catalytic converter and main catalytic converter on vehicles with automatic gearbox 01V
- VW: Front exhaust pipe with catalytic converters in the cylinder head - installation sequence
- AUDI: Checking Lambda probes and Lambda control after catalytic converter - vehicles with engine code letters "“ARE”", "“AZA”" and "“BES”"
- VW: Removing and installing Lambda probe 3 after catalytic converter G287 and Lambda probe 4 after catalytic converter G288
- VW: Removing and installing catalytic converter
- AUDI: Removing and installing front exhaust pipe (right-side) with catalytic converter - vehicles with multitronic gearbox
- AUDI: Checking Lambda probe and Lambda control before catalytic converter
- AUDI: Removing and installing front exhaust pipe (left-side) with starter catalytic converter and main catalytic converter (vehicles with automatic gearbox)
Who makes these pages, and how
TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.
The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.
The same code can mean different things on different makes. Match the meaning to your make before acting on it.
Seen a figure that does not match your manual? Write to us — we correct it and note when. support@torqfix.com
The story behind TorqFix →