P0031
2AZ-FXE ENGINE CONTROL SYSTEM: SFI SYSTEM: P0031,P0032: Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
CAUTION / NOTICE / HINT
HINT
- Although the DTC titles say oxygen sensor, these DTCs relate to the Air Fuel Ratio (A/F) sensor.
- Sensor 1 refers to the sensor mounted in front of the Three-Way Catalytic Converter (TWC) and located near the engine assembly.
DESCRIPTION
Refer to DTC P2195 P2195.
HINT
- When either of these DTCs is set, the ECM (included in hybrid vehicle control ECU) enters fail-safe mode. In fail-safe mode, the ECM turns off the A/F 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 A/F sensor heater circuit uses a relay on the B+ side of the circuit.
MONITOR DESCRIPTION
The ECM (included in the hybrid vehicle control ECU) uses information from the Air-Fuel Ratio (A/F) sensor to regulate the air-fuel ratio and keep it close to the stoichiometric level. This maximizes the ability of the Three-Way Catalytic Converter (TWC) to clean the exhaust gases.
The A/F sensor detects oxygen levels in the exhaust gas and transmits the information to the ECM. The inner surface of the sensor element is exposed to the outside air. The outer surface of the sensor element is exposed to the exhaust gas. The sensor element is made of platinum coated zirconia and includes an integrated heating element.
The zirconia element generates a small voltage when there is a large difference in the oxygen concentrations between the exhaust gas and outside air. The platinum coating amplifies this voltage generation.
The A/F sensor is more efficient when heated. When the exhaust gas temperature is low, the sensor cannot generate useful voltage signals without supplementary heating. The ECM regulates the supplementary heating using a duty-cycle approach to adjust the average current in the sensor heater element. If the heater current is outside the normal range, the signal transmitted by the A/F sensor becomes inaccurate, as a result, the ECM is unable to regulate air-fuel ratio properly.
When the current in the A/F sensor heater is outside the normal operating range, the ECM interprets this as a malfunction in the sensor heater and sets a DTC.
Example:
The ECM sets DTC P0032 when the current in the A/F sensor heater is more than 10 A. Conversely, when the heater current is less than 0.8 A, DTC P0031 is set.
MONITOR STRATEGY
TYPICAL ENABLING CONDITIONS
All:
All::
P0031:
P0031::
P0032:
P0032::
TYPICAL MALFUNCTION THRESHOLDS
P0031:
P0031::
P0032:
P0032::
COMPONENT OPERATING RANGE
WIRING DIAGRAM
Refer to DTC P2195 P2195.
INSPECTION PROCEDURE
HINT
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 AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
(a) Disconnect the C15 A/F sensor connector.
(b) Measure the resistance according to the value(s) in the table below.
Standard resistance:
(c) Reconnect the A/F sensor connector.
NG -- REPLACE AIR FUEL RATIO SENSOR Removal
OK -- Continue to next step.
2. CHECK TERMINAL VOLTAGE (+B OF A/F SENSOR)
(a) Disconnect the C15 A/F sensor connector.
(b) Turn the power switch on (IG).
(c) Measure the voltage between the terminal of the C15 A/F sensor connector and body ground.
Standard voltage:
(d) Reconnect the A/F sensor connector.
OK -- CHECK HARNESS AND CONNECTOR (A/F SENSOR - HYBRID VEHICLE CONTROL ECU)
NG -- Continue to next step.
3. INSPECT INTEGRATION RELAY (EFI RELAY)
(a) Remove the integration relay from the engine room R/B and J/B.
(b) Inspect the EFI relay.
(1) Measure the EFI relay resistance.
Standard resistance:
(c) Reinstall the integration relay.
NG -- REPLACE INTEGRATION RELAY
OK -- Continue to next step.
4. CHECK HARNESS AND CONNECTOR (A/F SENSOR - EFI RELAY)
(a) Disconnect the C15 A/F sensor connector.
(b) Remove the integration relay from the engine room R/B and J/B.
(c) Measure the resistance.
Standard resistance (Check for open):
Standard resistance (Check for short):
(d) Reconnect the A/F sensor connector.
(e) Reinstall the integration relay.
NG -- REPAIR OR REPLACE HARNESS OR CONNECTOR
OK -- CHECK ECM POWER SOURCE CIRCUIT
5. CHECK HARNESS AND CONNECTOR (A/F SENSOR - HYBRID VEHICLE CONTROL ECU)
(a) Disconnect the C15 A/F 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 A/F 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 Inspection Mode Procedure.
(f) Allow the engine to idle for 1 minute or more.
(g) Select the following menu items: Powertrain / Engine / Trouble Code.
(h) Read the DTCs.
Result:
B -- REPLACE HYBRID VEHICLE CONTROL ECU Removal
A -- CHECK FOR INTERMITTENT PROBLEMS Check for Intermittent Problems