P0138 on 2007-2011 Toyota Camry Hybrid: O2 Sensor High Voltage Causes & Fixes

What's Unique About the 2007-2011 Toyota Camry

While P0138 is a generic code, Toyota has issued Technical Service Bulletins (TSBs) for this issue on the Camry platform. For non-hybrid 2010-2011 models with the 2AR-FE engine, a TSB suggests the cause could be incorrect air/fuel ratio sensor response, fixed with an ECM update. However, for the 2.4L 2AZ-FE Hybrid engine covered here, the problem is more straightforward and almost always traces back to the downstream O2 sensor itself or its wiring, rather than complex software issues. Owner forums overwhelmingly confirm that a sensor replacement is the definitive fix.

Symptoms You May Notice

• Check Engine Light is on
• Poor fuel economy
• Rough idling or engine hesitation
• Failed emissions test

Most Likely Causes

1. Failed Downstream Oxygen Sensor (Bank 1, Sensor 2) 🔴 High Probability Oxygen sensors are wear-and-tear items that degrade over time from constant exposure to high-temperature exhaust gases. After many years and miles, their internal components can fail, leading to a short or incorrect voltage output. This is the most common failure for P0138 on this vehicle.
   How to confirm: Use an OBD-II scanner to monitor the live data for the B1S2 O2 sensor. If the voltage is stuck high (e.g., >0.9V) and does not fluctuate, the sensor is likely faulty. A video from YouTuber 'Car Medic' shows the sensor on a 2007 Camry Hybrid giving a constant high reading, confirming the failure before replacement.
   Typical fix: Replace the downstream oxygen sensor. This requires a 22mm O2 sensor socket and penetrating oil to loosen the old sensor. The torque spec for the new sensor is 32 ft-lbs.
   Est. part cost: $60 - $150
2. Damaged Wiring or Connector 🟡 Medium Probability The sensor's wiring harness runs underneath the vehicle and is exposed to road debris, moisture, and extreme heat from the exhaust, which can cause wires to melt, corrode, or break over time. A short to power in the signal wire will cause a persistent high voltage reading.
   How to confirm: Visually inspect the wiring harness leading to the downstream O2 sensor for any signs of melting, chafing, or corrosion at the connector. Use a multimeter to check for a short to power in the signal wire. On some Toyota models, owners have reported accidentally swapping the connectors for the two downstream sensors after a transmission repair, which can also cause this code.
   Typical fix: Repair or replace the damaged section of the wiring harness or clean the connector terminals.
   Est. part cost: $10 - $100
3. Engine Running Rich ⚪ Low Probability Issues like a leaking fuel injector or a faulty fuel pressure regulator can cause too much fuel to enter the engine. This unburnt fuel travels down the exhaust, causing the downstream O2 sensor to correctly read a high voltage (rich condition).
   How to confirm: Look for other diagnostic trouble codes related to the fuel system or air/fuel ratio sensors (e.g., P2195, P2197). Check long-term and short-term fuel trim values with a scan tool; consistently negative values indicate the ECM is trying to correct a rich condition.
   Typical fix: Diagnose and repair the root cause of the rich condition, such as replacing a faulty fuel injector.
   Est. part cost: $100 - $400

Rare But Worth Checking

• Faulty Engine Control Module (ECM): While uncommon, the ECM itself can fail. A TSB for the non-hybrid Camry with the 2AR-FE engine points to ECM logic as a potential cause, requiring a software update. This is a last-resort diagnosis after ruling out the sensor and wiring.
• Exhaust Leak: An exhaust leak *before* the upstream Air/Fuel Ratio sensor can trick the ECM into adding too much fuel, causing a genuinely rich condition that the downstream sensor detects. This would typically set other codes as well.

Diagnosis Steps

1. Confirm the code P0138 is present using an OBD-II scanner.
2. Access the live data stream on the scanner and observe the voltage for 'O2S B1S2' (Oxygen Sensor, Bank 1, Sensor 2).
3. Confirm the voltage is stuck high, typically above 0.8V or 0.9V, and does not fluctuate during normal operation.
4. Visually inspect the downstream O2 sensor's wiring harness and connector for any signs of melting, corrosion, or physical damage. The sensor is located after the flex pipe on the exhaust.
5. If the wiring appears intact, the most likely cause is a failed sensor.
6. To be certain, you can unplug the sensor. If the voltage on the scan tool drops to a low, default value, it confirms the sensor was sending the high voltage signal and should be replaced. If the voltage stays high, there is a short to power in the vehicle's wiring harness that needs to be found and repaired.
7. If replacing the sensor does not resolve the code, further investigation into a rich running condition or a potential ECM issue is needed.

Parts You'll Likely Need

• Downstream Oxygen Sensor (Bank 1, Sensor 2) (OEM #89465-06150) — This sensor is the most common failure point for code P0138. It is a standard maintenance item that wears out over time. This part number is confirmed by multiple Toyota parts dealers.
  Trusted brands: Denso (OEM), Bosch
  OEM price range: $100-$150
  Aftermarket price range: $60-$90

Related Codes That Often Appear With This One

• P0137 — O2 Sensor Circuit Low Voltage. Seeing both high and low voltage codes can indicate an intermittently failing sensor or wiring.
• P2195 — A/F Sensor Signal Stuck Lean (Bank 1, Sensor 1). As mentioned in TSB T-SB-0001-10 Rev, a problem with the upstream sensor can cause fuel trim issues that lead to a P0138 code downstream.
• P0031 — Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1, Sensor 1). A user on a Toyota forum reported having both P0138 and P0031 intermittently, pointing to a more complex electrical issue or multiple failing components.

Technical Service Bulletins (TSBs) & Recalls

• T-SB-0151-18: Mentions P0138 on 2010-2011 Camry with 2AR-FE (non-hybrid) engine, caused by incorrect air-fuel ratio sensor response requiring an ECM logic update.
• T-SB-0001-10 Rev: Notes that P0138 can occur on some vehicles, sometimes along with A/F sensor codes.

Platform-Specific Known Issues

• Toyota issued TSB T-SB-0151-18 for P0138 on 2010-2011 Camrys, but it applies to the non-hybrid 2AR-FE engine and points to an ECM logic issue. While not directly applicable to the 2AZ-FE Hybrid, it shows a history of P0138-related issues on the Camry platform.
• TSB T-SB-0001-10 Rev also notes that P0138 can appear on some Toyota vehicles, sometimes in conjunction with A/F sensor codes like P2195 or P2197.

Mechanic-Grade Diagnostic Values

• Downstream O2 Sensor (B1S2) Voltage at Idle (Warm Engine) — expected: Relatively stable voltage, drifting lazily above 0.5V.. Failure: Voltage is stuck high, at or above 0.8V - 0.9V, and does not fluctuate.
• Long Term Fuel Trim (LTFT) — expected: Should average near 0%.. Failure: Consistently positive values (e.g., +10% or more) can indicate the ECM is compensating for a perceived lean condition, which might be caused by a faulty upstream A/F sensor, leading to a genuinely rich exhaust that the downstream sensor correctly reads as high voltage.
• O2 Sensor Heater Resistance — expected: Typically between 11 and 16 Ohms at room temperature, but varies by specific sensor model.. Failure: An open circuit (infinite resistance) or a short (near zero resistance) indicates a failed heater element, which can affect sensor performance but usually sets a different DTC (e.g., P0141).

Scan Tool Commands That Help

• Techstream: Active Test: Control the Injection Volume for A/F sensor — This test, described in TSB T-SB-0151-18 for the non-hybrid, can be used to manually force the engine rich or lean. While performing this, you can monitor the B1S2 voltage to see if it responds accordingly. If the voltage stays high even when forcing a lean condition, it strongly points to a faulty sensor or a circuit short.

Wiring & Ground Locations

• Engine Control Module (ECM) — Located behind the right side of the dashboard.. The ECM receives the voltage signal from the O2 sensor. A poor connection at the ECM pin for the O2 sensor signal could cause a high voltage reading, though this is rare.
• Engine to Chassis Ground — There are multiple grounds. A key one runs from the chassis to the transmission housing, located under the airbox. Another runs from the negative battery terminal to the chassis.. A poor engine or sensor ground can cause floating voltages and erratic sensor readings, potentially leading to a P0138 code.
• A/F Sensor Fuse — In the engine compartment fuse box (also called Engine Room R/B), located on the driver's side by the fender.. The O2 sensor heater circuit is protected by a fuse, often labeled 'A/F HEATER' or similar. While a blown fuse typically causes a heater circuit code (P0141), it's a good practice to check all related fuses when diagnosing electrical faults.

Real Owner Repair Stories

• YouTube user 'Repairs and Reviews' (2007 Toyota Camry Hybrid) — Check engine light with code P0138.
  ✅ What actually fixed it The owner replaced the downstream oxygen sensor (Bank 1, Sensor 2) located after the flex pipe. The video shows the old sensor was a Denso part, and it was replaced with a new Denso sensor. This resolved the check engine light.

OEM Part Supersession History

• 89465-33440 → 89465-06150 — Standard part number update by Toyota.
  Heads up: The new part number (89465-06150) is the correct and current replacement for the original.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Excessive Oil Consumption 🔴 High — Very common on 2007-2009 models with the 2AZ-FE engine due to a piston ring design flaw. Can require adding a quart of oil every 1,000-1,200 miles. (Ref: T-SB-0094-11 (later superseded by T-SB-0030-15) detailed a repair procedure involving replacing the pistons and piston rings. A warranty enhancement program existed but has since expired.)
• Brake Actuator Assembly Failure 🔴 High — Common across the 2007-2011 Camry Hybrid range. Failure results in multiple brake-related warning lights and can cause inconsistent or jerky braking. (Ref: Toyota issued a Warranty Enhancement Program (ZE1 / ZJB) extending coverage for the brake actuator and skid control ECU for 10 years or 150,000 miles, but this has now expired for all affected model years.)
• Melting/Sticky Dashboard 🟡 Low — Widespread issue where sun and heat cause the dashboard material to become soft, shiny, and sticky, creating glare on the windshield. (Ref: A previous Customer Support Program to replace the dashboards existed but has long since expired.)
• Clogged HV Battery Cooling Filter/Fan 🟠 Medium — Common over the life of the vehicle, especially for owners with pets. Debris clogs the intake filter for the hybrid battery, reducing cooling and potentially causing 'Check Hybrid System' warnings and loud fan noise. (Ref: T-SB-0062-20 Rev1 provides a maintenance procedure for inspecting and cleaning the filter and fan assembly.)
• Water Pump Leak 🟠 Medium — A potential failure point as the vehicle ages. Leaks are typically slow and identified by a coolant smell or dried pink/orange residue near the front of the engine.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used oxygen sensor is almost never a good choice. It is a wear-and-tear item with a finite lifespan. The cost savings are minimal compared to the risk of the used part failing shortly after installation, requiring you to perform the labor again.

Donor-vehicle mileage cap: roughly under 50000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• If considering used, only pull from a very low-mileage wreck.
• Inspect the wiring for any signs of brittleness, melting, or damage.
• Check the sensor tip for heavy carbon deposits or white, chalky contamination, which indicates a poor-running donor engine.

OEM-only on this vehicle (don't cheap out):

• Oxygen Sensor

Aftermarket brands forum-validated for this vehicle:

• Denso (OEM manufacturer). The Denso aftermarket part (e.g., 234-4622) is widely reported by owners and mechanics to be identical to the Toyota-branded OEM part and is the most recommended choice.

Brands owners have reported issues with on this vehicle:

• While brands like Bosch are reputable, many Toyota specialists and forum users report a higher incidence of compatibility issues, premature failure, or slightly different voltage readings with non-Denso sensors on Toyota platforms. It is strongly recommended to stick with Denso.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P2195 — An Air/Fuel Ratio sensor code (Bank 1 Sensor 1) that TSB T-SB-0001-10 Rev notes can sometimes appear in conjunction with P0138.
• P2197 — An Air/Fuel Ratio sensor code (Bank 2 Sensor 1) that may occur alongside P0138 according to Toyota technical service bulletins.
• P0172 — A 'System Too Rich' code that may be related if the P0138 is caused by a genuine rich running condition, such as a leaking fuel injector, rather than a sensor failure.
• C1241 — While not an engine code, this relates to the Brake Actuator/Skid Control system which is a known common failure point on the 2007-2011 Camry Hybrid platform.

Frequently Asked Questions