Lambda (oxygen) sensor
Definition
The lambda sensor measures residual oxygen in the exhaust so the ECU can hold the air-fuel ratio near stoichiometric (lambda = 1). Narrowband zirconia sensors switch between about 0.1 and 0.9 V around lambda 1; wideband (air-fuel ratio) sensors output a current proportional to lambda and are used upstream on modern engines. The sensor needs roughly 300 °C to work, so it has an integrated heater; the downstream sensor mainly monitors catalyst efficiency. Failures include slow response from contamination (oil, coolant, silicone), heater circuit breaks and wiring chafed by heat. Codes: P0130-P0141 (bank 1), P0150-P0161 (bank 2), heater codes P0030-P0038, plus fuel trim codes P0171/P0172 when readings drift.
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Codes often stored
- P0030HO2S Heater Control Circuit
- P0130O2 Sensor Circuit (Bank 1, Sensor 1)
- P0131O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)
- P0133O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)
- P0135O2 Sensor Heater Circuit (Bank 1 Sensor 1)
- P0136O2 Sensor Circuit (Bank 1, Sensor 2)
- P0141O2 Sensor Heater Circuit (Bank 1 Sensor 2)
- P0171System Too Lean (Bank 1)
- P0172System Too Rich (Bank 1)