P0037

1ZZ-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

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.

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 ECM provides a pulse width modulated control circuit to adjust the current through the heater. 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 0.25 A, DTC P0037 is set.

MONITOR STRATEGY

TYPICAL ENABLING CONDITIONS

All:

P0037:

P0038 Case 1:

P0038 Case 2:

P0141 (Heater performance monitor check):

TYPICAL MALFUNCTION THRESHOLDS

P0037:

P0038 Case 1:

P0038 Case 2:

P0141 (Heater performance monitor check):

COMPONENT OPERATING RANGE

MONITOR RESULT

The monitor result (mode 6) allows the OBD scan tool to display the monitor status, test value and test limit.
A problem in this component can be found by comparing the test value and test limit. This procedure is described in "CHECKING MONITOR STATUS" (Mode 6 Data).

- TID (Test Identification) is assigned to each emission-related component.
- TLT (Test Limit Type):
If TLT is 0, the component is malfunctioning when the test value is higher than the test limit.
If TLT is 1, the component is malfunctioning when the test value is lower than the test limit.
- CID (Component Identification) is assigned to each test value.
- Unit Conversion is used to calculate the test value indicated on generic OBD scan tools.

TID $04: HO2S Heater

WIRING DIAGRAM

INSPECTION PROCEDURE

HINT: Read freeze frame data using 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 H8 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 R/B.
(b) Check the EFI relay resistance.
Standard resistance:

(a) Turn the ignition switch to the ON position.
(b) Measure the voltage between the terminals of the E4 ECM connector.
Standard voltage:

OK -- REPLACE ECM
NG -- Continue to next step.
4. CHECK HARNESS AND CONNECTOR

(a) Check the harness and connector between the ECM and HO2 sensor.
(1) Disconnect the H8 HO2 sensor connector.
(2) Disconnect the E4 ECM connector.
(3) Check the resistance.
Standard resistance (Check for open):

Standard resistance (Check for short):

(4) Reconnect the HO2 sensor connector.
(5) Reconnect the ECM connector.

(b) Check the harness and connector between the HO2 sensor and EFI relay.
(1) Inspect the EFI2 fuse.

- Remove the EFI2 fuse from the engine room R/B.
- Check the EFI2 fuse resistance.
Standard resistance:
Below 1 Ohms
- Reinstall the EFI2 fuse.

(2) Disconnect the H8 HO2 sensor connector.
(3) Remove the EFI relay from the engine room R/B.
(4) Check the resistance.
Standard resistance (Check for open):

Standard resistance (Check for short):

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