OBD-II Code · Sensors
P0155
O2 Sensor Heater Circuit (B2S1)
Bank 2 upstream heater failure.
Common symptoms
- CEL
Likely causes
- Failed heater
- Fuse
- Wiring
Where to start
- Try the cheapest cause first. Start by checking: failed heater.
- Cost & scope. $150-$350
- If the code returns after the fix: escalate to a shop or scanner with live-data and freeze-frame. A code that re-sets means the underlying fault is still there.
Read the full diagnostic procedure
P0155 is a heater-circuit fault on bank 2 upstream — bank-2 mirror of P0135. Heater current draw outside spec window: open, shorted, or implausible. Ohm the heater pins (6-15Ω cold narrow-band, 2-4Ω wideband); open = sensor heater coil failed (replace sensor). Verify B+ at heater feed pin and pulsed ground at heater control pin from the ECU. Frequently sets together with P0135 (bank 1) when both sensors are the same age and a shared O2 heater fuse blows — check the fuse before swapping parts. On longitudinal pickup trucks, bank 2 is usually passenger side; on transverse V6, bank 2 is the front bank. Verify before reaching for the sensor.
Vehicle-specific patterns
Vehicle-specific patterns: 2003-2008 Toyota Tundra / Sequoia 4.7L 2UZ-FE — longitudinal, bank 2 is passenger side; throws P0155 around 130k miles routinely. 2005-2010 Chrysler 300 / Charger 5.7L Hemi — TIPM relay failure causes simultaneous P0135 + P0155 (sensors fine; TIPM is the actual problem). 2007-2014 Cadillac CTS / SRX 3.6L LFX — transverse, bank 2 is front; throws P0155 from connector corrosion in the road-spray zone. 2010-2016 Audi Q5 / A4 2.0T quattro — sets P0155 from a chafed bank-2 wideband harness against the engine cradle. Cost band: $200-$500 sensor; up to $700+ if TIPM-related on Mopar; $25-$80 if just a fuse or connector.
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