Engine Fault light on
Diagnostic code P0036 P0037 or P0056 P0057
The diagnostic code refers to HO2S Heater Control Circuit and a likely open circuit. It could also be the supply fuse however the heaters of the O2 sensors are prone to go due to age 30-40Kmile +
A rough and ready check of the sensors:
The heater of these sensors can can be checked for continuity using a multimeter set to ohms.
Disconnect the sensor (Black connector). Bank 2 is at the front of the car, Bank 1 near the bulkhead.
On the sensor side connector measure across the two pins connected to the 2 black wires from the sensor.
A reading 5 ohms and below (nom 2.5) is good.
Equally a resistance below 2.5 ohm may indicate a short circuit, but this will also be indicated with a blown fuse.
You will need a 22mm spanner to remove Bank 2 sensor and a special tool to remove Bank 1 sensor
If possible remove the sensor and heat it using a hot air gun (paint remover or similar not a hair dryer) monitor the resistance of the heater to ensure that it dos not go open circuit at temperature.
While you have the sensor out
If you also measure across the other two wires using a multimeter set to mV you should see the output of the sensor rise towards 0.1 volt as it heats up.
These are not 100% tests but give a good indication