{"model":"mk4","model_name":"MK4 Supra","vehicle":"Toyota Supra A80 (1993–2002, 2JZ-GE / 2JZ-GTE)","document":"Repair Manual","section":"TGE","section_name":"Troubleshooting 2JZ-GE","page":39,"pages_in_section":105,"title":"Dtc 21 28 (Main Heated*1) Oxygen Sensor Circuit","section_header":"Engine — 2JZ-GE Engine Troubleshooting","ocr_text":"EG–419\nENGINE – 2JZ–GE ENGINE TROUBLESHOOTING\n\nDTC 21 28 (Main Heated*1) Oxygen Sensor Circuit\n\nCIRCUIT DESCRIPTION\nTo obtain a high purification rate for the Co, Hc and NOx components of the exhaust gas, a three–way catalytic\nconverter is used, but for most efficient use of the three–way catalytic converter, the air–fuel ratio must be pre-\ncisely controlled so that it is always close to the stoichiometric air–fuel ratio.\n\nThe oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoi-\nchiometric air–fuel ratio. This characteristic is used to detect the oxygen concentration in the exhaust gas and\nprovide feedback to the computer for control of the air fuel ratio.\n\nWhen the air–fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the oxygen sen-\nsor informs the ECM of the LEAN condition (small electromotive force: 0 V).\n\nWhen the air–fuel ratio is RICHER than the stoichiometric air–fuel ratio the oxygen concentration in the exhaust\ngas is reduced and the oxygen sensor informs the ECM of the RICH condition (large electromotive force: V).\n\nThe ECM judges by the electromotive force from the oxygen sensor whether the air–fuel ratio is RICH or LEAn\nand controls the injection duration accordingly. However, if malfunction of the oxygen sensor causes an output\nof abnormal electromotive force, the ECM is unable to perform accurate air–fuel ratio control.\nThe main heated oxygen sensors include a heater which heats the Zirconia element. The heater is controlled *1\nby the ECM. When the intake air volume is low t(the temperature of the exhaust has is low) current flows to\nthe heater to heat the sensor for accurate oxygen concentration detection.)\n\nAtmosphere\nIdeal Air–Fuel Mixture\n\nFlange\nPlatinum Electrode\nSolid Electrolyte\n(Zirconia Element)\nPlatinum Electrode\nHeater*1\nCoating (Ceramic)\n\nOutput Voltage\n\nRicher — Air Fuel ratio — Leaner\n\nCover\nF14835\nSS0076\nExhaust Gas\n\nDTC No. | Diagnostic Trouble Code Detecting Condition | Trouble Area\n\n(1)*1 Open or snort in heater circuit of main heated\noxygen sensor for 0.5 sec. or more.\n• Open or short in heater circuit of main heated\noxygen sensor\n• Main heated oxygen sensor heater\n• ECM\n\n(2) (Main heated*1) oxygen sensor signal voltage is\nreduced to between 0.35 V and 0.70 V for 60\nsec. under conditions (a) ~ (d):\n(2) trip detection logic)*2\n21\n•\n28\n(a) Engine coolant temp.: Between 80°C\n(176°F and 95°C (203°F)\n(b) Engine speed: 1,500 rpm or more\n(c) Load driving (Example A/T in Overdrive\n(5th for M/T), A/C ON, Flat road, 80 km/h (50\nmph))\n(d) (Main heated*1) oxygen sensor signal\nvoltage: Alternating above and below 0.45 V\n• (Main heated*1) oxygen sensor circuit\n• (Main heated*1) oxygen sensor\n\nHINT: Diagnostic trouble code \"21\" is for the (main heated*1) oxygen sensor (Fr) circuit.\nDiagnostic trouble code \"28\" is for the (main heated*1) oxygen sensor (Rr) circuit.\n*1: Main heated oxygen sensor ONLY for California specification vehicles.\n*2: See page 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transcript of a scanned Toyota factory manual page; verify critical values (torque specs, part numbers) against the image."}