P0037
2AZ-FXE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0037,P0038,P0141: 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 carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (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. To monitor the TWC, a Heated Oxygen (HO2) sensor is used.
The HO2 sensor is located behind the TWC, to detect the oxygen concentration in the exhaust gas. Since the sensor has an integrated heater for its 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 great. The HO2 sensor informs the ECM that the post-TWC oxygen concentration is great (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 small. The HO2 sensor informs the ECM that the post-TWC oxygen concentration is small (high voltage, i.e. more than 0.45 V). The HO2 sensor output voltage changes drastically when the air-fuel ratio is close to the stoichiometric level.
The ECM uses the supplementary information from the HO2 sensor to determine the oxygen concentration after the TWC, and adjusts the fuel injection time accordingly. Thus, if the HO2 sensor is working improperly due to internal malfunctions, the ECM will be unable to monitor TWC operation.
HINT:
- When any of these DTCs are set, the ECM (included in the hybrid vehicle control ECU) enters fail-safe mode. In fail-safe mode, the ECM turns off the Heated Oxygen (HO2) sensor heater. Fail-safe mode continues until the power switch is turned off.
- The ECM provides a pulse width modulated control circuit to adjust the current through the heater. The HO2 sensor heater circuit uses a relay on the B+ side of the circuit.
MONITOR DESCRIPTION
The sensing position 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 (included in the hybrid vehicle control ECU) supplements the heat from the exhaust with heat from a heating element inside the sensor.
Heated oxygen sensor heater range check (P0037 and P0038):
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 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 (Condition A):
P0038 (Condition B):
P0141 (Heater performance monitor check):
TYPICAL MALFUNCTION THRESHOLDS
P0037:
P0038:
P0141 (Heater performance monitor check):
COMPONENT OPERATING RANGE
WIRING DIAGRAM
CONFIRMATION DRIVING PATTERN
These DTCs are detected when the engine idles for 110 seconds or more.
INSPECTION PROCEDURE
HINT: Sensor 2 refers to the sensor mounted behind the Three-Way Catalytic Converter (TWC) and located far from the engine assembly.
Read freeze frame data using the Techstream. The ECM (included in the hybrid vehicle control ECU) records vehicle and driving condition information as freeze frame data the moment a DTC is stored. When troubleshooting, freeze frame data can help determine if the vehicle was moving or stationary, if the engine was warmed up or not, if the air-fuel ratio was lean or rich, and other data from the time the malfunction occurred.
PROCEDURE
1. INSPECT HEATED OXYGEN SENSOR (HEATER RESISTANCE)
(a) Disconnect the C22 Heated Oxygen (HO2) sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
(c) Reconnect the HO2 sensor connector.
NG -- REPLACE HEATED OXYGEN SENSOR
OK -- Continue to next step.
2. CHECK TERMINAL VOLTAGE (+B OF HO2 SENSOR)
(a) Disconnect the C22 HO2 sensor connector.
(b) Turn the power switch on (IG).
(c) Measure the voltage between the terminal of the C22 HO2 sensor connector and body ground.
Standard voltage:
(d) Reconnect the HO2 sensor connector.
OK -- CHECK HARNESS AND CONNECTOR (HO2 SENSOR - HYBRID VEHICLE CONTROL ECU)
NG -- Continue to next step.
3. INSPECT INTEGRATION RELAY (EFI RELAY) P0031
NG -- REPLACE INTEGRATION RELAY
OK -- Continue to next step.
4. CHECK HARNESS AND CONNECTOR (HO2 SENSOR - EFI RELAY)
(a) Check the EFI No. 3 fuse.
(b) Disconnect the C22 HO2 sensor connector.
(c) Remove the integration relay from the engine room R/B and J/B.
(d) Measure the resistance.
Standard resistance (Check for open):
Standard resistance (Check for short):
(e) Reconnect the HO2 sensor connector.
(f) Reinstall the integration relay.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- CHECK ECM POWER SOURCE CIRCUIT
5. CHECK HARNESS AND CONNECTOR (HO2 SENSOR - HYBRID VEHICLE CONTROL ECU)
(a) Disconnect the C22 HO2 sensor connector.
(b) Disconnect the C64 hybrid vehicle control ECU connector.
(c) Measure the resistance.
Standard resistance (Check for open):
Standard resistance (Check for short):
(d) Reconnect the HO2 sensor connector.
(e) Reconnect the hybrid vehicle control ECU connector.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- Continue to next step.
6. CHECK WHETHER DTC OUTPUT RECURS
(a) Connect the Techstream to the DLC3.
(b) Turn the power switch on (IG).
(c) Turn the tester on.
(d) Clear the DTCs DTC Check / Clear.
(e) Put the engine in inspection mode Component Tests and General Diagnostics.
(f) Allow the engine to idle for 2 minutes or more.
(g) Select the following menu items: Powertrain / Engine / Trouble Code.
(h) Read the DTCs.
Result:
B -- REPLACE HYBRID VEHICLE CONTROL ECU
A -- CHECK FOR INTERMITTENT PROBLEMS