P0138 on Toyota
O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)
P0138 on Toyota vehicles indicates o2 sensor circuit high voltage (bank 1, sensor 2). Au7o has documented this code across 3 Toyota models — most commonly on Camry, Highlander, Matrix. The PCM detects a persistently high voltage from the Bank 1, Sensor 2 downstream O2 sensor, indicating a short to voltage, contamination, or a rich condition at the post-catalyst sensor. Typical repair costs on Toyota range from $150 to $1,400, depending on the specific model and root cause.
Common Causes of P0138
- •Faulty downstream O2 sensor
- •Short to voltage in signal wire
- •Coolant/contaminant on sensor
- •Rich exhaust condition
- •Wiring/connector fault
P0138 on Toyota by Model
Toyota Camry(1 issue)
- 2007-2010 2GR-FE P0138/P0158/P0606 Diagnostic Gates - T-SB-0001-102007-2010
Toyota T-SB-0001-10 Rev1 covers specified 2007-2009 Camry VDS BK46K and 2010 VDS BK3EK applications. P0138/P0158 may result from incorrect air-fuel-sensor response, and P0606 may also be present due to incorrect downstream O2-sensor operation. Toyota distinguishes these paths using the complete DTC set, freeze-frame air-fuel/O2 voltage and downstream O2 impedance, followed by circuit inspection. It does not describe every P0606 as a sensor fault or support the original 2AZ-FE, 2006-2012, VSC/TRAC or battery claims.
Toyota Highlander(1 issue)
- Air/Fuel Ratio Sensor Signal Stuck Lean — P2195 / P2197 with P0138 / P0158 (2GR-FE)2008-2013
Second-generation Highlanders with the 2GR-FE V6 commonly set a check engine light for an upstream air/fuel ratio sensor whose signal sticks on the lean side of its range. The characteristic Toyota pattern is a downstream oxygen sensor circuit-high code (P0138 bank 1 or P0158 bank 2) appearing together with, or instead of, the A/F sensor code (P2195 bank 1, P2197 bank 2) — the ECM flags the rear sensor because the front sensor's slow response drives the fuel trim, so shops that replace the downstream O2 sensor first fix nothing. Toyota published a service bulletin covering 2008-2010 Highlander for exactly this combination, attributing it to incorrect air/fuel ratio sensor response. Symptoms are mild — a light, slightly worse fuel economy, occasional rough idle — but the car will fail emissions testing.
Toyota Matrix(1 issue)
- Catalyst Efficiency Failure (P0420) Driven by Oil Consumption and Aged O2 Sensors2003-2013
P0420 is among the most frequently reported check-engine complaints on the Matrix and its Pontiac Vibe twin. On these cars it is rarely a converter that simply wore out in isolation. Two upstream causes dominate: the aged downstream oxygen sensor whose switching becomes too lazy for the ECM's efficiency comparison, and on higher-mileage 1ZZ-FE engines the oil consumption problem, where burned oil leaves phosphorus and zinc deposits that foul the sensors and coat the converter substrate. Vibe owners on the shared platform document long, expensive chases where a new converter and new sensors did not clear the code because the underlying oil burn was never addressed. Exhaust leaks upstream of the rear sensor produce the same code by admitting extra oxygen.
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View P0138 across all makes →Frequently Asked Questions
What does P0138 mean on Toyota?▼
P0138 stands for "O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)." The PCM detects a persistently high voltage from the Bank 1, Sensor 2 downstream O2 sensor, indicating a short to voltage, contamination, or a rich condition at the post-catalyst sensor. On Toyota specifically, this code is documented across 3 models.
What causes P0138 on Toyota vehicles?▼
Common causes on Toyota: Faulty downstream O2 sensor, Short to voltage in signal wire, Coolant/contaminant on sensor, Rich exhaust condition, Wiring/connector fault. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0138 on a Toyota?▼
Repair costs on Toyota range from $150 to $1,400, depending on the specific model and root cause.
Which Toyota models have P0138 documented?▼
Au7o has documented P0138 on 3 Toyota models: Camry, Highlander, Matrix.