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DTC codes / Mazda codes / P1136

P1136 · MazdaHO2S Bank 1 Sensor 1 Heater Circuit High Input

P1136 on a Mazda means the powertrain control module (PCM) has detected an abnormally high voltage on the heater circuit of the upstream heated oxygen sensor (HO2S) in bank 1, sensor 1. The PCM expects the heater circuit to draw current and pull the voltage low when commanded on, so a high-voltage reading tells the module the circuit is open, has excessive resistance, or is shorted to voltage.

SystemPowertrain
Code typeMazda specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with no other symptoms besides the warning light
  • A pending or stored P1136 with no noticeable change in engine performance
  • Slightly longer time to enter closed-loop fuel control after a cold start, which can cause a brief rich-running smell
  • Intermittent check engine light that comes and goes with vibration or temperature changes
  • In rare cases, a slight decrease in fuel economy if the sensor heater never reaches operating temperature

Common causes, most likely first

  1. Open or broken wire in the HO2S heater power or ground circuit, often at the sensor connector or where the harness flexes near the exhaust
  2. Failed oxygen sensor heater element, typically an internal open circuit in the sensor itself
  3. Corroded, loose, or water-intruded connector pins at the HO2S or at the PCM
  4. Blown fuse that supplies the oxygen sensor heater circuit, sometimes shared with other emissions components
  5. Short to voltage on the heater control wire, which can be caused by chafed insulation against a nearby power wire
  6. PCM driver circuit fault on the heater control side, though this is less common than wiring or sensor failure

How to diagnose and fix it

  1. Connect a scan tool and confirm P1136 is current or pending, then check for any related oxygen sensor or heater circuit codes before proceeding
  2. Inspect the HO2S bank 1 sensor 1 connector and the full length of its harness for corrosion, chafing, or a broken wire, and repair as needed
  3. Check the oxygen sensor heater fuse in the underhood fuse box and replace it if blown, then recheck for a short before returning the vehicle
  4. Measure resistance across the two heater terminals of the HO2S with a multimeter; an open circuit or a reading far outside the manufacturer's specification confirms a failed sensor
  5. With the key on and the sensor disconnected, measure voltage on the heater power supply wire to verify battery voltage is present and the ground side has continuity
  6. Command the heater on with a scan tool and measure the voltage on the control wire to see whether the PCM is pulling the circuit low; if not, check the PCM driver and wiring
  7. Replace the HO2S bank 1 sensor 1 if the heater element is open or the circuit tests normal but the code returns, then clear codes and verify the repair with a road test

What a high-voltage heater code really means

  • A high-voltage reading on the heater circuit almost always means the circuit is open, so the PCM sees full supply voltage on the control wire instead of the expected pulled-down voltage.
  • Technicians often replace the oxygen sensor first, but a corroded connector or a broken wire near the exhaust manifold is just as common and costs far less to fix.
  • The heater fuse for the upstream oxygen sensor on many Mazdas is shared with other emissions components, so a blown fuse can set multiple codes and should be checked before condemning the sensor.
  • A sensor that tests good on resistance can still set P1136 intermittently if the heater circuit opens only when the engine bay is hot or the harness is flexed, so wiggle-test the wiring while watching live data.
  • P1136 does not mean the oxygen sensor's signal circuit is faulty; the sensor may still report air-fuel ratio correctly once the engine is warm, which is why drivability symptoms are often absent.

Can I keep driving with P1136?

You can usually drive the vehicle with P1136 because the engine will still run, but the oxygen sensor heater may not reach operating temperature quickly, which can affect emissions and cold-start fuel control. Avoid long-term driving with the light on and get the circuit inspected soon, especially if you notice a rich-running smell or reduced fuel economy.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Mazda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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