Sub Oxygen Sensor

Toyota does not provide any information for testing the sub oxygen sensor directly. If the engine control module (ECM) detects a problem with the sub oxygen sensor, diagnostic trouble code (DTC) 27 will be set. The conditions for setting DTC 27 are as follows:
a. Engine coolant temperature above 80° C (176° F)
b. Engine speed above 1,500 rpm
c. Accelerator pedal is fully depressed for 2 seconds or more
d. Main Oxygen signal is 0.45 volts or more and the sub oxygen sensor signal is 0.45 volts or less

NOTE: DTC 27 uses 2 trip detection logic. For a description, see 2 Trip Detection Logic Defined under the Trouble Code Charts in Computers and Control Systems Testing Procedures.
Testing and Inspection