P0135 on the 2020 Toyota Tundra
The 2020 Toyota Tundra runs the 3UR-FE 5.7-liter i-Force V8 engine producing 381 horsepower and 401 lb-ft of torque. A P0135 code means the heater circuit in the Bank 1, Sensor 1 oxygen sensor has malfunctioned. On the Tundra's longitudinally mounted V8, Bank 1 is the driver's side (left side) cylinder bank. The upstream O2 sensor on this bank monitors exhaust gases before they enter the catalytic converter.
V8 Exhaust System Layout
The 5.7L V8 has two separate exhaust manifolds feeding into two catalytic converters, one per bank. Each bank has its own upstream and downstream O2 sensor. The Bank 1 upstream sensor is threaded into the driver-side exhaust manifold. The heater element inside the sensor draws approximately 2 to 4 amps and must bring the sensor to 600°F operating temperature within 20 to 30 seconds of a cold start for proper closed-loop fuel control.
What Causes P0135 on the Tundra V8
- Heater element burnout (High Likelihood): At four to five years old, the Denso OEM sensor's heater coil can fail from thermal fatigue. The V8's hotter exhaust temperatures and higher flow rates stress the heater element more than in smaller engines. Tundras used for towing generate even higher exhaust temperatures that accelerate wear.
- Wiring damage along the frame (Medium Likelihood): The sensor wiring on the Tundra runs along the frame rail from the exhaust manifold to the ECM. Road debris, salt, and moisture can damage insulation or corrode connections along this path. Full-size trucks are more exposed to underbody hazards.
- Blown heater fuse (Medium Likelihood): Check the underhood relay/fuse box for the O2 heater fuse. On the V8, this fuse may serve both banks. If you also see P0155, the fuse is the prime suspect.
- Exhaust manifold or header bolt issues (Low Likelihood): The Tundra V8 is known for exhaust manifold bolt failures. While this does not directly cause P0135, exhaust leaks near the sensor can affect its readings and potentially damage the wiring from excess heat exposure at the leak point.
Diagnosis Walkthrough
Sensor Location and Access
The Bank 1 upstream sensor on the Tundra V8 is on the driver-side exhaust manifold. You can access it from above with a long extension or from underneath the truck. The full-size truck's generous ground clearance makes underbody access easier than on cars. However, the sensor may be in a tight spot between the manifold and the frame rail.
Fuse Check
Start with the O2 heater fuse in the engine compartment fuse box. Pull it and test. If blown, replace and clear codes.
Resistance Testing
Disconnect the sensor and measure heater resistance across the heater pins. Expect 2 to 14 ohms for a functional Denso sensor. Open circuit means the heater coil is burned out. While the sensor is disconnected, verify battery voltage at the harness connector with the key on.
Check for Exhaust Leaks
The 5.7L V8 has a documented history of exhaust manifold bolt failures. While this does not directly cause P0135, listen for ticking sounds on cold start that quiet down as the engine warms. Exhaust leaks near the O2 sensor can introduce false air readings and stress the sensor wiring with excess heat.
Repair Costs
The 2020 Tundra should be within the 8-year/80,000-mile federal emissions warranty. Check with your Toyota dealer first. Out of pocket: OEM Denso sensor for the 5.7L V8 costs $90 to $170. Shop labor runs $100 to $180 depending on sensor accessibility. Total: $190 to $350. DIY is feasible on the Tundra thanks to the truck's clearance, but budget extra time for seized threads on a five-year-old exhaust component. Use a 22mm O2 sensor socket and generous penetrating oil.
The Full-Size Truck Factor
The Tundra's 5.7L V8 consumes more fuel than four-cylinder engines even in optimal conditions. A failed O2 sensor heater adding two to five minutes of rich cold-start operation wastes more total fuel on a V8 than on a smaller engine. For Tundra owners making short trips or daily commutes, the fuel economy penalty is noticeable. Fix the sensor to keep the already thirsty V8 running as efficiently as possible.