DTC 28

Data Trouble Code No. 21 - Main Heated Oxygen Sensor (left) Signal

Detecting Condition

Open or short in heater circuit of Main Heated Oxygen Sensor (left) for 0.5 seconds or more
or
Main Heated Oxygen Sensor (left) voltage is reduced to between 0.35 volts and 0.70 volts for 60 seconds under the following conditions (2 trip detection):

- Engine Coolant Temperature between 80°C (176°F) and 95°C (203°F).
- Engine Speed 1,500 rpm or more.
- Load driving i.e., transmission in overdrive, air conditioning on, 80 km/h (50 mph).
- Main Heated Oxygen Sensor (left) voltage alternating above and below 0.45 volts.

Trouble Area

- Open or short in heater circuit of Main Heated Oxygen Sensor (left)
- Main Heated Oxygen Sensor (left) circuit.
- Main Heated Oxygen Sensor (left).
or
- Main Heated Oxygen Sensor (left) circuit.
- Main Heated Oxygen Sensor (left).

Malfunction Indicator Lamp

Normal Mode On
Test Mode On

Code 21 And 28 Description:

Circuit description
The oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoichiometric air-fuel ratio. This characteristic is used to detect the oxygen concentration in the exhaust gas and provide feedback to the computer for control of the air-fuel ratio.

When the air-fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the oxygen sensor informs the engine control module of the LEAN condition (small electromotive force: 0 V).

When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio the oxygen concentration in the exhaust gas is reduced and the oxygen sensor informs the engine control module of the RICH condition (large electromotive force: 1 V).

The engine control module judges by the electromotive force from the oxygen sensor whether the air-fuel ratio is RICH or LEAN and controls the injection time accordingly. However, if malfunction of the oxygen sensor causes output of abnormal electromotive force, the engine control module is unable to perform accurate air-fuel ratio control.

The main heated oxygen sensors include a heater which heats the Zirconia element. The heater is controlled by the engine control module. When the intake air volume is low (the temperature of the exhaust gas is low) current flows to the heater to heat the sensor for accurate oxygen concentration detection.

HINT: Diagnostic trouble code 21 is for the left bank main heated oxygen sensor circuit. Diagnostic trouble code 28 is for the right bank main heated oxygen sonsor circuit.

DTC Detection Driving Pattern:

DTC Detection Driving Pattern

Code 21 And 28 Diagnostic Chart And Wiring Diagram:

DTC Diagnostic Chart and Wiring Diagram

Code 21 And 28 Inspection Procedure:

Code 21 And 28 Inspection Procedure - Page 2:

DTC Inspection Procedures