Toyota P1135 Code Meaning
The heater inside Toyota's upstream air/fuel ratio sensor is drawing too much or too little current.
At a glance
Severity: Low
- Meaning
- A/F Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $20–$1,500
- DIY difficulty
- Moderate
Many Toyota and Lexus engines from the late 1990s to the mid-2000s use a Denso air/fuel ratio (A/F) sensor ahead of the catalytic converter instead of a conventional oxygen sensor, and Toyota reports its heater faults with P1135 rather than the generic P0135 or P0031. An A/F sensor has to run hotter than a normal O2 sensor, so its heater is far more powerful and has a very low resistance. The ECM measures the heater current directly: if it goes above roughly 8 A (short) or stays below a lower limit (3 A on many engines) while the heater is switched on, on two consecutive drive cycles, P1135 is stored. Bank 1 Sensor 1 is the only upstream sensor on four-cylinder engines like the 2AZ-FE in the Camry and RAV4, and the rear, firewall-side manifold sensor on transverse V6 engines. Most of the time the heater element itself has burned open.
Can I keep driving? You can keep driving; the engine simply stays in open-loop fueling a little longer after each cold start. Plan the repair within a few weeks, because fuel use rises and the car won't pass an emissions test.
How to read P1135
- P Powertrain
- 1 Manufacturer-specific
- 1 Fuel & air metering
- 35 Specific fault
Symptoms
- Check engine light on, usually after the fault has shown up on two separate drives
- Fuel economy a few mpg worse, most noticeable on short trips and in cold weather
- Engine runs slightly rich or sluggish for the first minutes after a cold start
- A/F sensor and heater readiness monitors stay incomplete
- Once fully warm, the car often drives completely normally
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Heater element inside the A/F sensor burned open
- Heat-damaged wiring or corroded, loose pins between the EFI relay, the sensor and the ECM
- Blown heater fuse, usually caused by a shorted heater or a pinched wire
- Non-Denso or wrong-spec replacement sensor whose heater draws current outside Toyota's window
- Worn EFI main relay contacts or low supply voltage to the heater
- Heater driver inside the ECM failed
Diagnosis step by step
Make sure you have the right sensor
On a four-cylinder the A/F sensor sits in the exhaust manifold or front pipe ahead of the catalytic converter; on a transverse V6 bank 1 is the rear bank against the firewall. The downstream sensor behind the converter is a conventional O2 sensor and is not the one P1135 refers to.
Tools: Flashlight
Check the heater supply
Toyota feeds the heater with battery voltage from the EFI main relay and switches it on the ground side. With the key on, back-probe the supply pin at the sensor connector: you should see about 12 V. No voltage means checking the EFI or A/F heater fuse in the underhood box and the relay first.
Tools: Multimeter
Measure the heater resistance
Unplug the sensor and measure across the two heater pins on the sensor side. Toyota A/F heaters are very low resistance, roughly 1 to 3.5 ohms at 68 °F depending on the sensor generation, so short your meter leads together first and subtract that reading. An open circuit or a value far outside the manual's spec condemns the sensor.
Tools: Multimeter
Test the ECM side of the circuit
Reconnect everything and turn the key on. At the heater control terminal of the ECM (marked HTAF on Toyota wiring diagrams) you should read roughly 9 to 14 V, which proves supply, heater and harness are continuous. If that voltage is present and the heater measured good, the ECM's heater driver becomes the suspect.
Tools: Multimeter
Inspect the harness route
Follow the sensor lead from the manifold to its connector bracket and look for melted insulation, missing clips or contact with the exhaust heat shield. Wiggle the harness with the key on while watching the supply voltage; a reading that drops out points to a broken wire under intact insulation.
Tools: Flashlight, Multimeter
Replace, clear and confirm
Fit an OE-type Denso A/F sensor with anti-seize on the threads only, torque it to spec and clear the code. Because of Toyota's two-trip logic, drive through at least two cold starts before assuming the repair is complete.
Tools: O2 sensor socket, Torque wrench, OBD-II scanner
Where the parts are
- 1Upstream O2 sensor
- 2Catalytic converter
- 3Downstream O2 sensor
- 4Diesel particulate filter
- 5Turbocharger
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace A/F sensor bank 1 sensor 1 (four-cylinder) | Yes | $200–$450 |
| Replace A/F sensor on rear bank of a transverse V6 | No | $300–$650 |
| Replace heater fuse and trace the short | Yes | $20–$150 |
| Repair heat-damaged sensor harness or connector | No | $100–$300 |
| Replace and program ECM | No | $600–$1,500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
P1135 keeps the check engine light on and blocks the A/F heater monitor, so the car fails an OBD smog check. After the repair, several cold starts followed by normal driving are needed before the monitors report ready.
Frequently asked questions
Why does my Toyota show P1135 instead of P0135?
Because the engine uses an air/fuel ratio sensor, not a conventional oxygen sensor. Toyota gave A/F sensor faults their own P1xxx numbers on engines of this era; later models report the same heater fault with standard P0030-series codes.
Can I install a cheaper universal oxygen sensor?
No. A universal O2 sensor is a different type of sensor with a different signal and heater, and the ECM will either set P1135 again or run poorly. Use an A/F sensor that matches the original Denso part for your engine.
I replaced the sensor and P1135 came back. Now what?
Check the heater fuse, the supply voltage at the connector and the harness near the manifold, then the ECM heater driver. An aftermarket sensor with a heater that draws slightly different current can also trip Toyota's current-based check.
Will P1135 damage the catalytic converter?
Not directly. The engine runs a bit richer for longer after cold starts, which costs fuel, but the converter is not at immediate risk. Fixing it promptly keeps fuel trims and emissions where they belong.
Sources
- Manufacturer public service information (cross-checked)
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