P0135 on a 2012 Toyota Tacoma
O2 Sensor Heater Circuit (Bank 1 Upstream)
P0135 on a 2012 Toyota Tacoma indicates o2 sensor heater circuit (bank 1 upstream). It usually stays drivable short-term but should be diagnosed promptly. The most common cause is failed o2 sensor heater element (open or shorted internally) (typically $150–$450). Confirm the root cause before replacing parts.
What does P0135 mean on a 2012 Toyota Tacoma?
P0135 is set when the ECM detects that the heater element built into the Bank 1 upstream oxygen sensor is not drawing the expected current when commanded on. Zirconium O2 sensors only produce a usable signal above approximately 350 °C / 660 °F, so they include an internal heater that brings them to operating temperature quickly after cold start. P0135 means that heater is open, shorted, or being under-powered.
This guide covers P0135 across the 2010-2014 Toyota Tacoma generation — the symptoms, causes, and diagnostic steps below apply to every model year from 2010 through 2014.
Is it safe to drive a 2012 Toyota Tacoma with P0135?
In most cases a 2012 Toyota Tacoma stays drivable for short trips with P0135 active, but diagnose and repair it promptly. This is a moderate-severity code — ignoring it can lead to further damage or a failed emissions test.
What are the symptoms of P0135 on a 2012 Toyota Tacoma?
- Check Engine Light is illuminated
- Extended open-loop fuel-trim period after cold start (worse fuel economy until warm)
- Slow O2 sensor switching that may take several minutes to begin after cold start
- Possible drivability symptoms if the engine remains in open loop too long
- Vehicle may fail emissions / smog test
What causes P0135 on a 2012 Toyota Tacoma?
| Cause | Likelihood | Estimated repair (USD) |
|---|---|---|
| Failed O2 sensor heater element (open or shorted internally) | Most common | $150–$450 |
| Blown O2 heater fuse Always check the fuse before condemning the sensor. | Common | $5–$30 |
| Damaged sensor wiring (chafed against exhaust) | Common | $80–$350 |
| Corroded O2 sensor connector | Common | $30–$200 |
| Failed O2 heater relay (on vehicles with one) | Occasional | $30–$150 |
| Failed PCM driver for the heater circuit (rare) | Rare | $400–$1,500 |
How to diagnose this on a 2012 Toyota Tacoma
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Check the O2 heater fuse first
Most vehicles route O2 heater power through a dedicated fuse, usually labeled "O2H" or "O2 SNSR" in the underhood fuse box. Replace any blown fuse with the exact amperage rating. If the fuse blows again immediately, the heater or its wiring is shorted.
Tools: Replacement fuse, Fuse puller
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Measure heater resistance at the sensor
Unplug the Bank 1 upstream O2 sensor. Measure resistance across the heater terminals (typically the two same-color wires — consult the wiring diagram). Expected resistance is approximately 3 to 15 Ω cold, depending on the sensor. Infinite resistance means an open heater; near zero means a shorted heater.
Tools: Multimeter, Wiring diagram
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Verify power and ground at the connector
With the key on and engine running, back-probe the heater power and ground wires. Battery voltage should be present on power and a clean ground on the other side. Missing voltage points to the fuse, the wiring, or the PCM driver.
Tools: Multimeter, Back-probe pins
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Measure heater current draw
A working heater draws approximately 0.8 to 2 A depending on sensor design. Use a low-current clamp around the heater wire, or a multimeter in series. Current of 0 A with voltage present means the heater is open. Current well above 2 A means the heater is partially shorted and will fail soon.
Tools: Multimeter with current function, Low-current clamp (preferred)
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Inspect the sensor and its wiring for physical damage
O2 sensor harnesses run close to hot exhaust components and are a common chafing victim. Inspect the wiring from the connector to the sensor body. Heat-damaged insulation, melted plastic, or visible copper requires harness repair or replacement, not just a new sensor.
Tools: Flashlight, Wire repair supplies
NHTSA complaints & recalls for the 2012 Toyota Tacoma
Owner-reported safety complaints and official recalls filed with the U.S. National Highway Traffic Safety Administration for the 2012 Toyota Tacoma. Use these to gauge how common a problem is on your specific vehicle before you start chasing Toyota Tacoma diagnostics.
- ENGINE 122
- POWER TRAIN 35
- VEHICLE SPEED CONTROL 22
- FUEL/PROPULSION SYSTEM 51
- UNKNOWN OR OTHER 43
7 active recalls
- STRUCTURE:BODY:HOOD:HINGE AND ATTACHMENTS Jul 2017
Southeast Toyota Distributors, LLC (SET) is recalling certain 2011-2016 Toyota Tacoma and 4Runner vehicles equipped with accessory hood scoops installed by SET or SET dealers. The adhesive attaching the hood scoop may weaken, allowing the hood scoop to detach from the vehicle.…
NHTSA campaign 17V425000 - SERVICE BRAKES, HYDRAULIC:ANTILOCK/TRACTION CONTROL/ELECTRONIC LIMITED SLIP:CONTROL UNIT/MODULE Feb 2014
Toyota is recalling certain model year 2012 and 2013 Toyota Tacoma and Lexus RX350 vehicles and certain model year 2012 Toyota Rav4 vehicles. In the affected vehicles, the brake system contains a brake actuator that adjusts the fluid pressure of each wheel cylinder. An electric…
NHTSA campaign 14V054000 - EQUIPMENT:OTHER:LABELS Aug 2014
Toyota Motor Engineering & Manufacturing (Toyota) is recalling certain model year 2008-2014 FJ Cruiser and Tacoma vehicles equipped with accessory wheels and tires installed by Toyota or dealers prior to the vehicle's first sale. The affected vehicles may list incorrect spare ti…
NHTSA campaign 14V475000 - TIRES:TEMPORARY/EMERGENCY SPARE TIRE Oct 2013
Southeast Toyota Distributors, LLC (SET) is recalling certain model year 2012-2013 Tacoma vehicles equipped with 18" Maverick Alloy Wheels. In the affected vehicles, the spare tire requires the use of a different style of lug nut to attach it to the vehicle than the other wheels…
NHTSA campaign 13V494000
How do I fix P0135 on a 2012 Toyota Tacoma?
- Replace the Bank 1 upstream O2 sensor with an OEM part
- Replace the O2 heater fuse
- Repair damaged O2 sensor wiring
- Replace the O2 heater relay
- Clean or repair the O2 sensor connector
About the 2010-2014 Toyota Tacoma
The 2010-2014 Toyota Tacoma was commonly sold with the following powertrains: 2.7L I4, 3.5L V6, 4.0L V6. Common trims include SR, SR5, TRD Sport, TRD Off-Road, Limited.
Why heater failure matters
Zirconium O2 sensors produce no usable signal until they reach about 350 °C. Without the heater, the sensor waits for exhaust heat to bring it up to temperature — which can take 5+ minutes of driving. During that period the ECM runs in “open loop” mode, using a calibrated fueling map rather than O2 feedback. This is fine briefly but causes poor cold-running emissions and 10–20 % worse fuel economy while the heater is dead.
P0135 with the sensor only weeks old
Aftermarket O2 sensors fail at much higher rates than OEM. If P0135 appeared shortly after an O2 sensor replacement with a non-OEM part, the new sensor itself is the most likely problem. Warranty-exchange for an OEM-equivalent before chasing the wiring.
Heater current and the “weak heater”
A heater that draws low current but is not fully open is a “weak” heater. It will warm the sensor partially, allowing the sensor to work but slowly. The ECM eventually sets P0135 even though the heater is not fully dead. A current measurement is the only reliable way to catch this failure mode — a simple resistance check often misses it.
P0135 on a 2012 Toyota Tacoma: frequently asked questions
What does diagnostic trouble code P0135 mean on a 2012 Toyota Tacoma?
P0135 is set when the ECM detects that the heater element built into the Bank 1 upstream oxygen sensor is not drawing the expected current when commanded on. Zirconium O2 sensors only produce a usable signal above approximately 350 °C / 660 °F, so they include an internal heater that brings them to operating temperature quickly after cold start. P0135 means that heater is open, shorted, or being under-powered.
What are the symptoms of P0135 on a 2012 Toyota Tacoma?
Check Engine Light is illuminated. Extended open-loop fuel-trim period after cold start (worse fuel economy until warm). Slow O2 sensor switching that may take several minutes to begin after cold start. Possible drivability symptoms if the engine remains in open loop too long. Vehicle may fail emissions / smog test
What causes P0135 on a 2012 Toyota Tacoma?
Failed O2 sensor heater element (open or shorted internally) (most-common). Blown O2 heater fuse (common). Damaged sensor wiring (chafed against exhaust) (common). Corroded O2 sensor connector (common). Failed O2 heater relay (on vehicles with one) (occasional). Failed PCM driver for the heater circuit (rare) (rare)
Is it safe to drive a 2012 Toyota Tacoma with P0135?
In most cases a 2012 Toyota Tacoma stays drivable for short trips with P0135 active, but it should be diagnosed and repaired promptly — this is a moderate-severity code. Ignoring it can lead to further damage or a failed emissions test.