What does it mean?
OBD II fault code P0059 is defined as “Heated Oxygen Sensor Resistance (Bank 2 Sensor 1)”, and is set when the PCM (Powertrain Control Module) detects an electrical resistance in the sensor control circuit that falls outside of predefined parameters. On engines with two cylinder heads, “Bank 2” refers to the bank of cylinders that does not contain cylinder #1, while “Sensor 1” refers to the oxygen sensor that is located upstream of the catalytic converter.
Code P0059 indicates a problem with the electrical resistance of the control circuit, and while high or low resistance issues can occur in the control circuit wiring and even the PCM, it is more likely that the issue involves the internal resistance of the actual oxygen sensor itself, rather than the control circuit or the PCM.
Typically, the resistance in this circuit will be 8 Ohms (or very close to it), and a variation of around 10% to either side of this value will set code P0059 and illuminate the CHECK ENGINE light. Oxygen sensors play a critical role in the calculation of fuel delivery, ignition-, and valve timing strategies by comparing the amount of oxygen in the exhaust stream (before it enters the catalytic converter) with the oxygen content of the ambient atmosphere.
As the oxygen content of the exhaust stream changes continually during normal engine operation, the oxygen sensor uses the varying oxygen content of the exhaust gas to generate signal voltages that vary from about 100 millivolts to around 900 millivolts. The resulting signal voltages are used by the PCM to command changes in fuel trim, ignition timing, as well as valve timing on engines where VVT or VCS timing systems are fitted.
A properly functioning oxygen sensor that is at its proper operating temperature (about 350 0 C) reacts to variations in the oxygen content of the exhaust gas almost immediately, thus ensuring that the PCM is always able to manage the engine efficiently, regardless of the engine load or speed.
NOTE#1: While the resistance value of 8 Ohms stated here is valid for the majority of applications that use conventional oxygen sensors, the manual for the application being worked on should always be consulted for the exact values for that application. NOTE #2: Some Japanese vehicles, such as Toyota, use AIR/FUEL RATIO sensors that are NOT interchangeable with conventional oxygen sensors.
Consult the relevant manual for the correct diagnostic, testing, and repair information for these applications. The image below shows the typical construction of a heated oxygen sensor. Note the location of the heater element, which requires a specific electrical resistance to warm up to several hundred degrees before the sensor will start to generate a signal voltage.