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Severity: Low Code type: Manufacturer-specific (Toyota)

Toyota P1155 Code Meaning

The heater in the front-bank air/fuel ratio sensor of a Toyota V6 or V8 is out of its current range.

At a glance

Severity: 2/5 – Low2/5

Severity: Low

Meaning
A/F Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
System
Fuel & Air Metering · Powertrain
Safe to drive?
Yes, short term
Typical repair cost
$30–$1,500
DIY difficulty
Easy

P1155 only exists on Toyota and Lexus V6 and V8 engines, because only they have a second bank. It is the bank 2 twin of P1135: the ECM watches the current through the heater of the upstream air/fuel ratio (A/F) sensor on the bank without cylinder 1 and flags it when the current is too high or too low while the heater is commanded on. On the transverse 3.0-liter 1MZ-FE found in the Camry, Solara, Avalon, Sienna, Highlander, ES 300 and RX 300 of this era, bank 2 is the front bank next to the radiator, so the sensor is reachable from the top of the engine bay. Depending on the emissions package, some versions of these vehicles use conventional oxygen sensors instead and would report P0155 for the same kind of fault. A burned-out heater is the usual cause, but P1155 appearing together with P1135 points to the shared supply instead.

Can I keep driving? Driving is fine in the short term; the engine only takes longer to reach closed-loop fueling after a cold start. Book the repair soon, since fuel use goes up slightly and the car will fail a smog check.

How to read P1155

How to read P1155P11213554
  1. P Powertrain
  2. 1 Manufacturer-specific
  3. 1 Fuel & air metering
  4. 55 Specific fault

Symptoms

  • Check engine light on after two drives with the fault
  • Slightly higher fuel use, mainly on short trips
  • Uneven warm-up behavior between the two banks shortly after a cold start
  • Front-bank A/F heater readiness monitor stays incomplete
  • No noticeable drivability change once the engine is warm

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Heater element in the bank 2 (front) A/F sensor burned open 42%
  2. Sensor pigtail or connector on the front manifold cooked by exhaust heat or loosened clip 16%
  3. Shared heater supply problem (fuse or EFI relay), typically when P1135 is stored as well 14%
  4. Aftermarket A/F sensor with a heater that does not match the Denso original 12%
  5. Engine oil from a leaking front valve cover gasket soaking the connector or sensor lead 9%
  6. Bank 2 heater driver in the ECM failed 7%

Diagnosis step by step

Diagnostic flow: P11551Read which heater codes are stored2Locate the bank 2 sensor3Compare both heaters4Check supply and control voltage5Look for oil and heat damage6Replace and verify

  1. Read which heater codes are stored

    If P1155 is stored alone, focus on the front sensor and its lead. If P1135 is present too, both heaters lost power at the same time, so start at the fuse and EFI relay they share rather than buying two sensors.

    Tools: OBD-II scanner

  2. Locate the bank 2 sensor

    On transverse V6 models the bank 2 A/F sensor threads into the front exhaust manifold, visible from above once the manifold heat shield or engine cover is off. On pickups and SUVs with a longitudinal V6 or V8, confirm which side is bank 2 in the repair manual before ordering parts.

    Tools: Flashlight

  3. Compare both heaters

    Measure heater resistance across the two heater pins of the front sensor, then do the same on the rear sensor. Two healthy Denso heaters of the same type read within a few tenths of an ohm of each other; an open circuit or a clearly different value on bank 2 identifies the bad one.

    Tools: Multimeter

  4. Check supply and control voltage

    With the key on and the sensor plugged in, the supply pin should show about 12 V and the bank 2 heater control terminal at the ECM roughly 9 to 14 V. Missing supply means a fuse or relay problem; supply present at the sensor but not at the ECM terminal means a broken wire in between.

    Tools: Multimeter

  5. Look for oil and heat damage

    Check the front valve cover edge and the connector bracket for oil wetness, and the lead for hardened or melted insulation. An oil-soaked connector can creep resistance and eventually lose contact, so fix the leak along with the sensor.

    Tools: Flashlight

  6. Replace and verify

    Install an OE-equivalent A/F sensor, route the lead through its original clips away from the manifold and clear the code. Drive through two cold starts and check that the heater monitor completes.

    Tools: O2 sensor socket, Torque wrench, OBD-II scanner

Where the parts are

Exhaust: catalytic converter and O2 sensors (Bank 1 / Bank 2) – P11551212345
Exhaust: catalytic converter and O2 sensors (Bank 1 / Bank 2)
  1. 1Upstream O2 sensor
  2. 2Catalytic converter
  3. 3Downstream O2 sensor
  4. 4Diesel particulate filter
  5. 5Turbocharger

Repair options & costs

RepairDIY?Estimated cost
Replace front-bank (bank 2) A/F sensor Yes $200–$450
Repair shared heater fuse or EFI relay circuit Yes $30–$180
Repair heat- or oil-damaged sensor harness No $100–$300
Replace front valve cover gasket to stop oil reaching the harness No $200–$450
Replace and program ECM No $600–$1,500

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Toyota

The 1MZ-FE V6 in Camry, Sienna, Highlander and related Lexus models numbers its banks with bank 1 at the firewall and bank 2 at the radiator, which makes the P1155 sensor the easier of the two to replace.

Emissions / smog test impact

Will fail

P1155 lights the check engine light, which is an automatic fail on an OBD-based smog test. After the sensor is replaced, drive a few cold-start cycles until the O2/A/F heater monitor reads complete.

Frequently asked questions

Which side is bank 2 on my Camry or Sienna V6?

On the transverse 1MZ-FE V6, bank 2 is the front bank closest to the radiator, and bank 1 with cylinder 1 is against the firewall. The P1155 sensor is therefore the front manifold sensor, usually reachable from above.

Should I replace both A/F sensors at the same time?

Only if the bank 1 heater also measures out of spec or P1135 is stored. Both sensors are the same age, so some owners replace them together at high mileage, but a healthy resistance reading on bank 1 means it is not required.

Why does my truck show P0155 while a friend's similar truck shows P1155?

Toyota fitted A/F sensors to some emissions versions and conventional oxygen sensors to others. A/F-equipped engines report the bank 2 heater with P1155, conventional sensors with P0155.

Can I swap the two sensors to test them?

It is possible on some engines, but the leads and connectors are often different lengths, so measuring and comparing heater resistance is quicker and just as conclusive.

Sources