P0036 is a very common O2 sensor-related trouble code. It’s generic, which means it has the same definition for the Mazda CX-8 as any other vehicle.
This code is almost always caused by a bad heated oxygen sensor or wiring issue and is almost always symptom-free.
P0036 should NOT be considered a breakdown risk if it appears by itself. Your CX-8’s engine relies heavily on the upstream sensor for engine tuning. B1S2 is downstream of the catalytic converter and primarily checks exhaust gas content for emissions purposes.
P0036 Definition: Heater Control – Circuit – B1S2
P0036 indicates no signal coming from your Mazda CX-8’s Bank1 Sensor 2 oxygen sensors heater circuit.
The heated element within the oxygen sensor heats the sensor faster than the exhaust can. The heated element reduces emissions by letting the fuel trim enter closed loop operation more quickly.
The A/F sensor is responsible for measuring the oxygen content of the exhaust. The PCM uses this data to adjust the air-fuel mixture to the optimal 14.7 parts air to 1 part fuel.
Circuit
In the case of P0036, the PCM has detected a fault in the circuit that activates the oxygen sensors heater.
Bank One
Bank one is the part of your CX-8’s engine with the first cylinder. You only need to concern yourself with “banks” if there is more than one cylinder head (4 cylinders and inline-six engine owners can skip this part).
Bank one is usually the cylinder head facing a little more forward than the other (toward the engine accessories).
Sensor 2
The second sensor is easier to identify. Start from bank one and follow the exhaust. It’ll be right after the catalytic converter.
P0036 Symptoms: Mazda CX-8
The heated element in the oxygen sensor enables closed-loop operation faster, decreasing engine emissions.
You probably won’t notice any drivability issues with your CX-8 since B1S2 is there to verify the catalytic converter is doing its job.
If your CX-8 had P0030 (the Bank 1 Sensor 1 version of this code), there would be more noticeable symptoms.
Mazda CX-8: P0036 Causes + Diagnosis
Here are the most common causes of P0036 in the Mazda CX-8, presented to you in a somewhat proper order of diagnosis:
1. Check the Wiring on Bank 1 Sensor 2
Since the PCM is not getting a response from the heated oxygen sensor circuit, check the wiring harness for damage.
Pay extra close attention to where the harness may have come into contact with something. Look for burnt or damaged wiring. Wiring issues are a VERY COMMON cause for P0036.
The hot exhaust makes wiring harnesses brittle, and road debris can damage them.
Take a look at where your CX-8’s oxygen sensor plugs into the wiring harness and see if there has been any damage to the pins or if the wiring harness is breaking at the pigtail.
If the pins appear corroded, get some electrical contact cleaner and clean them up. If they are damaged, you will need to repin or replace your wiring harness.
2. Check the Fuses and Voltage
Check the heated oxygen sensor fuse to ensure that it has not blown for some reason. Then, verify with the key on that there’s voltage at the oxygen sensor. If there is no voltage, you’ll need to find where the short/open is.
If there is voltage at the heater circuit, you’ll need to test the ground for resistance. If you find infinite resistance, you’ll need to repair the ground circuit.
3. Optional – Swap Test
If your Mazda CX-8 happens to be a V6 or V8 model, you can do the “swap test.” This involves clearing the codes and seeing if the code “jumps” to bank 2. It’s a great test because it’s foolproof and easy.
This also only works on vehicles with true dual exhaust, so there’s a strong chance you will not be able to do this.
Here’s how the swap test is done:
- Clear the DTC codes with your scanner.
- Swap the Bank 1 Sensor 2 O2 sensor with Bank 2 Sensor 2’s sensor.
- Run the your CX-8’s engine until the check engine light comes back on.
- If the code changes to P0056 (The Bank 2 version of this code), that’s proof enough you need to replace the oxygen sensor you swapped.
- If the code remains P0036, you’ll need to continue pursuing your diagnosis, knowing that both O2 sensors are working fine.
4. Bad Oxygen Sensor
If the oxygen sensor wiring checked out or failed the swap test, it’s time to replace the heated oxygen sensor. Oxygen sensors go bad all the time.
Conclusion
P0036 in the Mazda CX-8 is almost always caused by a bad wiring harness or oxygen sensor. Good luck!