schematics and diagrams: test heater circuit in car

Error code P0037, H025, BANK 1 SENSOR 2, HEATER CIRCUIT LOW.

This is the O2 sensor located behind the Cat on the back side of the engine exhaust manifold.

To determine if the heater is bad, a resistance reading can be made on the heater pins at the plug to the O2. These would be the connectors that the Light Green and Black/White wire on the engine harness connect too. There should be resistance of 14.2 to 18.9 ohms. Anything more or less of these values, replace the O2.

And in case of P0031, HO2S Bank 1 Sen 1
Heater Circuit Low
The firewall side of the engine is Bank 1 for the MPV, the radiator side is Bank 2. So that code is pointing to a problem in the heater circuit for the sensor near the firewall before the convertor. You can check resistance of the heater circuit of the sensor. If should have 5-7 ohms, if not then the sensor is definitely bad.

AND IN CASE OF
P0031 H02S BANK 1 SEN 1, HEATER CIRCUIT LOW, WHERE IS THIS SENSOR LOCATED AND IS IT UPSTREAM OR DOWNSTREAM.

THe Oxygen Sensor at Bank1 Sensor1 is mounted to the exhaust manifold on the side of the engine closest to the firewall. This is a "Sensor 1" so it is labeled as an "Upstream" sensor.

See the help diagram shown below:----

Mazda Sensor parts location

This details will help.
Thanks.

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You get check engine light on dash.In this case Engine computer module called ECM has to be scanned.
In scanning you get error code P0155.
This error code means.Bank 2 Sensor 1 heater failure.
This refers to the heater inside one of your oxygen sensors. The computer is not reading current to the heater. The problem may be the wires or the sensor itself. The thing to do is to check for voltage at the sensor connector with the key turned on. This particular sensor is right on the front of the engine by the radiator. If the voltage is there, the sensor is probably bad. You can also test the sensor heater with an ohmmeter as follows:
Testing Heating Element
Before Testing any electrical component, inspect the wiring and connectors for damage. Also wiggle the connectors to ensure a that they are firmly engaged.
Disconnect the electrical harness from each of the sensors.
The white wires in the sensor connector are the power and ground circuits for the heater.
Connect the ohmmeter test leads to the terminals of the white wires in the heated oxygen sensor connector.
Check the resistance of the sensor, if it is not within 4-7 ohms, replace the sensor.
The picture below is the sensor on bank 1, by the firewall. The one you want (bank 2, sensor 1) is on the front of the engine.

See the Sample diagram shown below :----

This details will help you.

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