P0133–P0165 O2 Sensor Circuit Slow Response Bank 1 Sensor 1
The sensor still reads correctly but reacts too slowly, which is the classic sign of an aged sensor rather than a wiring fault.
Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.
Which code is which
Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.
| Code | Definition | Severity |
|---|---|---|
P0133 | O2 Sensor Circuit Slow Response Bank 1 Sensor 1 | Investigate soon |
P0139 | O2 Sensor Circuit Slow Response Bank 1 Sensor 2 | Investigate soon |
P0145 | O2 Sensor Circuit Slow Response Bank 1 Sensor 3 | Investigate soon |
P0153 | O2 Sensor Circuit Slow Response Bank 2 Sensor 1 | Investigate soon |
P0159 | O2 Sensor Circuit Slow Response Bank 2 Sensor 2 | Investigate soon |
P0165 | O2 Sensor Circuit Slow Response Bank 2 Sensor 3 | Investigate soon |
The definition
P0133: O2 Sensor Circuit Slow Response Bank 1 Sensor 1.
P0133 is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.
What to check first
Cheapest and fastest checks first:
- Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
- Check the connector at the part for corrosion, and that it is fully seated.
- Clear the code and see whether it returns, and under what conditions.
What actually causes this on a VAG
The pre-cat lambda on bank 1 still works, but it's switching between rich and lean more slowly than the ECU expects - a lazy sensor. The ECU only runs this particular test in a fairly narrow set of driving conditions, so the light can appear after one long steady run and then stay away for days. It's not an emergency, but a slow sensor means less accurate mixture control and slightly worse fuel economy until it's dealt with.
Most likely causes, in order
- Old, tired sensor. This is the one lambda code where the sensor genuinely is the usual answer - they slow down with age, heat cycles and gradual contamination, and there's no cleaning one back to life. If it's the original sensor on a high-mileage car and the checks below come back clear, replacing it is a reasonable move.
- Small exhaust leak ahead of the sensor. Air sneaking in through a cracked manifold, a blowing gasket or a tired flexi pipe both slows and distorts the signal, and will happily set the same code on a brand-new sensor. Listen on a cold start for ticking or puffing that fades as everything heats up and seals.
- Weak sensor heater or its supply. The sensor has to stay hot to respond quickly, so a failing heater, a blown fuse or a poor earth on that circuit makes it sluggish at idle and in slow traffic. A heater-circuit code stored alongside this one points straight at the cause.
- Contamination from oil, coolant or sealant. An engine using oil or coolant gradually poisons the sensing element, as does silicone sealant used where the engine can breathe it in. Check consumption before fitting a new sensor, otherwise you're signing up for a replacement every so often.
Worth knowing: If you do replace it, fit the correct sensor for your engine rather than a universal one you splice into the existing lead - joins in the sensor's own wiring are a common reason this code comes straight back. And keep silicone sealant well away from anything the engine can draw in; it's a classic lambda killer.
Reading the code is the easy part
A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.
VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.
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Common questions
What does P0133 mean?
P0133 means O2 Sensor Circuit Slow Response Bank 1 Sensor 1. The sensor still reads correctly but reacts too slowly, which is the classic sign of an aged sensor rather than a wiring fault.
Can I drive with P0133?
The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.