P0155 on 2004-2010 Toyota Sienna — O2 Sensor Heater Circuit (Bank 2, Sensor 1)
1 vehicles · 1 makes · $220-$2,200 repair
How to diagnose and fix P0155: most-reported vehicles
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Toyota Sienna · 2004–2010
High-mileage XL20 Siennas commonly set P0420 (Bank 1) and sometimes P0430 (Bank 2) for catalyst efficiency below threshold. On this V6 layout Bank 1 is the rear (firewall) bank and Bank 2 the front, and the van carries four sensors: two upstream air/fuel ratio sensors and two downstream heated oxygen sensors. The most frequent real cause is a lazy downstream sensor whose switching has slowed with age, not a dead converter - but shops routinely quote catalytic converter replacement first, which on this van is a four-figure job. Exhaust leaks upstream of the rear sensor and unresolved misfires also set the code.
Common Symptoms
- Check engine light with catalyst efficiency code
- Slightly reduced fuel economy
- Failed state emissions inspection
- No drivability symptom in many cases
How to Fix
Before replacing a converter, graph the downstream sensor on a scan tool - a healthy rear sensor should sit relatively flat around 0.6-0.7V, while a sensor that mirrors the upstream switching is worn out. Also smoke-test or listen for exhaust leaks at the manifold and flange gaskets and clear any misfire codes first. A Denso or OEM downstream sensor is a few hundred dollars installed versus $1,200-$2,200 for the rear manifold converter, which sits against the firewall and is the labor-intensive one. No recall exists, though the converter may be covered under the federal 8-year/80,000-mile emissions warranty on vehicles still in that window.
Sources for this issue (3)
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P0155 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0155 mean?
P0155 stands for "O2 Sensor Heater Circuit (Bank 2, Sensor 1)." The PCM has tested the heater circuit of the Bank 2, Sensor 1 upstream O2 sensor and detected a malfunction. The heater brings the sensor to operating temperature for closed-loop control. Indicates a heater element or circuit fault.
What are the most common causes of P0155?
The most common causes of P0155 are: Failed O2 sensor heater element, Open or shorted heater wiring, Blown heater fuse, Corroded connector, Poor heater power/ground. The specific cause varies by vehicle.
How much does it cost to fix P0155?
Repair costs for P0155 range from $220 to $2,200, depending on the vehicle and root cause.
Which vehicles are affected by P0155?
Au7o has documented P0155 across 1 vehicle models from 1 manufacturers: Toyota.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.