SFI SYSTEM, Diagnostic DTC:P0037, P0038, P0057, P0058

DESCRIPTION

In order to obtain a high purification rate of the carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) components in the exhaust gas, a TWC (Three-Way Catalytic Converter) is used. For the most efficient use of the TWC, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel level. For the purpose of helping the ECM to deliver accurate air-fuel ratio control, a Heated Oxygen (HO2) sensor is used.

The HO2 sensor is located behind the TWC, and detects the oxygen concentration in the exhaust gas. Since the sensor is integrated with the heater that heats the sensing portion, it is possible to detect the oxygen concentration even when the intake air volume is low (the exhaust gas temperature is low).

When the air-fuel ratio becomes lean, the oxygen concentration in the exhaust gas is rich. The HO2 sensor informs the ECM that the post-TWC air-fuel ratio is lean (low voltage, i.e. less than 0.45 V).

Conversely, when the air-fuel ratio is richer than the stoichiometric air-fuel level, the oxygen concentration in the exhaust gas becomes lean. The HO2 sensor informs the ECM that the post-TWC air-fuel ratio is rich (high voltage, i.e. more than 0.45 V). The HO2 sensor has the property of changing its output voltage drastically when the air-fuel ratio is close to the stoichiometric level.

The ECM uses the supplementary information from the HO2 sensor to determine whether the air-fuel ratio after the TWC is rich or lean, and adjusts the fuel injection time accordingly. Thus, if the HO2 sensor is working improperly due to internal malfunctions, the ECM is unable to compensate for deviations in the primary air-fuel ratio control.

MONITOR DESCRIPTION

The sensing portion of the Heated Oxygen (HO2) sensor has a zirconia element which is used to detect the oxygen concentration in the exhaust gas. If the zirconia element is at the appropriate temperature, and the difference between the oxygen concentrations surrounding the inside and outside surfaces of the sensor is large, the zirconia element generates voltage signals. In order to increase the oxygen concentration detecting capacity of the zirconia element, the ECM supplements the heat from the exhaust with heat from a heating element inside the sensor.

Heated oxygen sensor heater range check (P0037, P0038, P0057 and P0058):

• The ECM monitors the current applied to the HO2 sensor heater to check the heater for malfunctions. If the current is below the threshold value, the ECM will determine that there is an open circuit in the heater. If the current is above the threshold value, the ECM will determine that there is a short circuit in the heater.




• Example:




• The ECM sets DTC P0038 or P0058 when the current in the HO2 sensor heater is more than 2 A. Conversely, when the heater current is less than 0.3 A, DTC P0037 or P0057 is set.

WIRING DIAGRAM

Refer to DTC P0136 Click here.

INSPECTION PROCEDURE

PROCEDURE

1. INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE)

   
   

   1. Turn the power switch off.

   2. 

      Disconnect the E65 or L49 heated oxygen sensor connector.

   3. Measure the resistance according to the value(s) in the table below.

      Standard resistance
      Bank 1 Sensor 2 Tester Connection Condition Specified Condition 1 (HT1B) - 2 (+B) 20°C (68°F) 11 to 16 Ω 1 (HT1B) - 4 (E2) Always 10 kΩ or higher
      Bank 2 Sensor 2 Tester Connection Condition Specified Condition 1 (HT2B) - 2 (+B) 20°C (68°F) 11 to 16 Ω 1 (HT2B) - 4 (E2) Always 10 kΩ or higher

   
   

   NG

   REPLACE HEATED OXYGEN SENSOR Click here

   OK

2. CHECK TERMINAL VOLTAGE (+B OF HEATED OXYGEN SENSOR)

   
   

   1. 

      Turn the power switch on (IG).

   2. Measure the voltage according to the value(s) in the table below.

      Standard voltage
      Bank 1 Sensor 2 Tester Connection Switch Condition Specified Condition E65-2 (+B) - Body ground Power switch on (IG) 11 to 14 V
      Bank 2 Sensor 2 Tester Connection Switch Condition Specified Condition L49-2 (+B) - Body ground Power switch on (IG) 11 to 14 V

   
   

   NG

   CHECK HARNESS AND CONNECTOR (ENGINE ROOM NO. 2 RELAY BLOCK - HEATED OXYGEN SENSOR) Click here

   OK

3. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - ECM)

   
   

   1. 

      Turn the power switch off.

   2. Disconnect the A13 ECM connector.

   3. Measure the resistance according to the value(s) in the table below.

      Standard resistance (Check for open)
      Terminal Connection Condition Specified Condition E65-1 (HT1B) - A13-4 (HT1B) Always Below 1 Ω L49-1 (HT2B) - A13-3 (HT2B) Always Below 1 Ω

      Standard resistance (Check for short)
      Terminal Connection Condition Specified Condition E65-1 (HT1B) or A13-4 (HT1B) - Body ground Always 10 kΩ or higher L49-1 (HT2B) or A13-3 (HT2B) - Body ground Always 10 kΩ or higher

   
   

   NG

   REPAIR OR REPLACE HARNESS OR CONNECTOR

   OK

   REPLACE ECM Click here

4. CHECK HARNESS AND CONNECTOR (ENGINE ROOM NO. 2 RELAY BLOCK - HEATED OXYGEN SENSOR)

   
   

   1. 

      Turn the power switch off.

   2. Remove the EFI relay (EFI MAIN2) from the engine room No. 2 relay block.

   3. Measure the resistance according to the value(s) in the table below.

      Standard resistance (Check for open)
      Terminal Connection Condition Specified Condition EFI MAIN2 relay (3) - E65-2 (+B) Always Below 1 Ω EFI MAIN2 relay (3) - L49-2 (+B) Always Below 1 Ω

      Standard resistance (Check for short)
      Terminal Connection Condition Specified Condition EFI MAIN2 relay (3) or E65-2 (+B) - Body ground Always 10 kΩ or higher EFI MAIN2 relay (3) or L49-2 (+B) - Body ground Always 10 kΩ or higher

   
   

   NG

   REPAIR OR REPLACE HARNESS OR CONNECTOR

   OK

   CHECK ECM POWER SOURCE CIRCUIT Click here