P0037

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

DESCRIPTION

A three-way catalytic converter (TWC) is used in order to convert the carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) into less harmful substances. To allow the TWC to function effectively, it is necessary to keep the air-fuel ratio of the engine near the stoichiometric air-fuel ratio. For the purpose of helping the ECM to deliver accurate air-fuel ratio control, the 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.

HINT:
- Sensor 2 refers to the sensor mounted behind the Three-Way Catalytic Converter (TWC) and located far from the engine assembly.
- When any of these DTCs are set, the ECM enters fail-safe mode. The ECM turns off the HO2 sensor heater in fail-safe mode. Fail-safe mode continues until the ignition switch is turned off.
- The Heated Oxygen (HO2) sensor heater circuit uses a relay on the +B side of the circuit.

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. When the current in the sensor heater is outside the standard operating range, the ECM interprets this as a malfunction in the sensor heater and sets a DTC.
Example:
The ECM sets DTC P0038 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 is set.

MONITOR STRATEGY

TYPICAL ENABLING CONDITIONS

All:

P0037:

P0038:

P0141:

TYPICAL MALFUNCTION THRESHOLDS

P0037:

P0038:

P0141 (Heater performance monitor check):

COMPONENT OPERATING RANGE

MONITOR RESULT

Refer to detailed information on "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 H5 Heated Oxygen (HO2) sensor connector.
(b) Measure the resistance between the terminals of the HO2 sensor connector.
Standard resistance:

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

(a) Remove the EFI relay from the engine room relay block.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:

(a) Turn the ignition switch to the ON position.
(b) Measure the voltage between the terminals of the E8 ECM connector.
Standard voltage:

NG -- CHECK WIRE HARNESS (HEATED OXYGEN SENSOR - ECM, EFI RELAY)
OK -- REPLACE ECM
4. CHECK WIRE HARNESS (HEATED OXYGEN SENSOR - ECM, EFI RELAY)

(a) Check the wire harness between the ECM and HO2 sensor.
(1) Disconnect the H5 HO2 sensor connector.
(2) Disconnect the E8 ECM connector.
(3) Measure the resistance according to the value(s) in the table below.
Standard resistance:

(4) Reconnect the HO2 sensor connector.
(5) Reconnect the ECM connector.
(b) Check the wire harness between the HO2 sensor and EFI relay.
(1) Disconnect the H5 HO2 sensor connector.
(2) Remove the EFI relay from the engine room relay block.
(3) Measure the resistance according to the value(s) in the table below.
Standard resistance:

(4) Reconnect the HO2 sensor connector.
(5) Reinstall the EFI relay.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- REPLACE ECM