Powertrain, generic · Fuel and air metering

P0133 O2 Sensor Circuit Slow Response Bank 1 Sensor 1

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The oxygen sensor before the catalytic converter on bank 1 (sensor 1) is the main control sensor for the mixture. It is either a switching sensor (about 0.1 V lean to 0.9 V rich) or a wide-band sensor that works with a pump current evaluated by an interface chip. P0133 means the sensor does not react fast enough to mixture changes. Methods differ fundamentally: GM measures passively how long the signal takes to cross 400–600 mV in each direction, averaged over 60 s; Ford forces the mixture to swing at 1.5 Hz and fails a switching sensor whose amplitude stays below 0.5 V, or evaluates response times of a wide-band sensor against a no-fault area; Subaru compares controller activity with measured lambda over 210 s. The test runs once per drive at warm part load; two trips. Mixture control usually stays active, but worse.

Likely causes

Aged, sooted or poisoned upstream sensor (oil, silicone, coolant, additives)
Exhaust leak ahead of the sensor (manifold gasket, crack)
Sensor heater weak or intermittent (sensor too cold)
Mixture fault: air leak, injectors, fuel pressure, air flow sensor
Wiring resistance or aftermarket sensor with different characteristics

Symptoms

  • Check engine light on (after two drive cycles)
  • Slightly higher consumption
  • Higher emissions, possible emissions test failure
  • P0420 may follow

Repair estimate

DifficultyEasyDIY possible
Parts and labour€60–300
Time0.5–1.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Check sensor switching speed
  2. Look for exhaust leaks
  3. Replace an aged sensor

Parts involved

oxygen sensor bank1 sensor1oxygen sensor wiringengine control module

Related codes

P0153P0134P0135P0171P0420P2195

References: law.cornell.edu, gsi.ext.gm.com, newtonnet.co.uk, saabwisonline.com.