P0037

2UZ-FE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0037: Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 2)

DTC P0037 - Oxygen Sensor Heater Control Circuit Low (Bank 1 Sensor 2)

DTC P0038 - Oxygen Sensor Heater Control Circuit High (Bank 1 Sensor 2)

DTC P0057 - Oxygen Sensor Heater Control Circuit Low (Bank 2 Sensor 2)

DTC P0058 - Oxygen Sensor Heater Control Circuit High (Bank 2 Sensor 2)

DTC P0141 - Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)

DTC P0161 - Oxygen Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)

DESCRIPTION
HINT: Sensor 2 refers to the sensor mounted behind the Three-Way Catalyst Converter (TWC) and located far from the engine assembly.

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 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 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.





HINT:
- When any of these DTCs are set, the ECM enters fail-safe mode. The ECM turns off the heated oxygen sensor heater in fail-safe mode continues until the ignition switch is turned OFF.
- The ECM provides a pulse width modulated control circuit to adjust the current through the heater. The heated oxygen sensor heater circuit uses a relay on the +B side of the circuit.









HINT:
- Bank 1 refers to the bank that includes No. 1 cylinder.
- Bank 2 refers to the bank that does not include No. 1 cylinder.
- Sensor 1 refers to the sensor closest to the engine assembly.
- Sensor 2 refers to the sensor farthest away from the engine assembly.

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 concentration 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 O2 sensor heater to check the heater for malfunctions. If the current is below the threshold value, the ECM determines that there is an open circuit in the heater. If the current is above the threshold value, the ECM determines that there is a short circuit in the heater.
The ECM constantly monitors the current applied to the heater. If the ECM detects an open or short circuit, the ECM turns the MIL on and sets a DTC.
If a malfunction is detected, the ECM cuts off the current applied to 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.

Heated oxygen sensor heater performance (P0141 and P0161):

After the accumulated heater ON time exceeds 100 seconds, the ECM calculates the heater resistance using the battery voltage and the current applied to the heater.
If the resistance is above the threshold value, the ECM determines that there is a malfunction in the HO2 sensor heater and sets DTC P0141 or P0161.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS

P0037 and P0057 (Low current):





P0038 and P0058 (High current):





P0141 and P0161





TYPICAL MALFUNCTION THRESHOLDS

P0037 and P0057 (Low current):





P0038 and P0058 (High current):





P0141 and P0161





COMPONENT OPERATING RANGE





MONITOR RESULT

Refer to CHECKING MONITOR STATUS Mode 6 Data.

WIRING DIAGRAM





INSPECTION PROCEDURE
HINT: Read freeze frame data using the Techstream. The ECM records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can be helpful in determining whether the vehicle was running or stopped, whether the engine was warmed up or not, whether the air/fuel ratio was lean or rich, as well as other data recorded at the time of a malfunction.

PROCEDURE

1. INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE)





(a) Disconnect the H6 or H8 Heated Oxygen (HO2) sensor connector.
(b) Measure the resistance of the HO2 sensor connector.
Standard resistance:





(c) Reconnect the HO2 sensor connectors.
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
2. INSPECT EFI RELAY





(a) Remove the EFI relay from the engine room R/B.
(b) Measure the resistance of the EFI relay.
Standard resistance:





(c) Reinstall the EFI relay.
NG -- REPLACE EFI RELAY
OK -- Continue to next step.
3. INSPECT ECM (HT1B OR HT2B VOLTAGE)





(a) Turn the ignition switch ON.
(b) Measure the voltage of the E5 and E6 ECM connectors.
Standard voltage:





HINT:
- The HT1B means the heated oxygen sensor bank 1 sensor 2.
- The HT2B means the heated oxygen sensor bank 2 sensor 2.

OK -- REPLACE ECM
NG -- Continue to next step.
4. CHECK HARNESS AND CONNECTOR (HEATED OXYGEN SENSOR - EFI RELAY, HEATED OXYGEN SENSOR - ECM)





(a) Turn the ignition switch OFF.
(b) Disconnect the H6 or H8 oxygen sensor connector.
(c) Disconnect the E5 and E6 ECM connectors.
(d) Measure the resistance.
Standard resistance (Check for open):






Standard resistance (Check for short):





(e) Remove the EFI relay from the engine room R/B.
(f) Measure the resistance.
Standard resistance (Check for open):






Standard resistance (Check for short):





(g) Reconnect the ECM connectors.
(h) Reconnect the oxygen sensor connectors.
(i) Reinstall the EFI relay.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE ECM