Lexus IS250 IS220d GSE20 ALE20 2AD-FHV ENGINE CONTROL SYSTEM
INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE)
CHECK TERMINAL VOLTAGE (A/F SENSOR HEATER VOLTAGE)
INSPECT AIR FUEL RATIO SENSOR RELAY
CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM, A/F SENSOR - A/F RELAY)
CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)
DTC P0031 Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)
DTC P0032 Oxygen (A/F) Sensor Heater Control Circuit High (Bank 1 Sensor 1)
DESCRIPTION
- HINT:
- *: Diesel Clean Advanced Technology.
The characteristic of the A/F sensor is such that it provides an output voltage (*1) that is proportional to the air-fuel ratio that it is measuring. The A/F sensor output voltage is used as feedback to allow the ECM to control the A/F mixture.
The A/F sensor is located after the Diesel Particulate-NOx Reduction (DPNR) catalytic converter. This sensor has been developed based on the structure and technology of the A/F sensor that is used for gasoline engine. The cover for the sensor electrode has been modified to suit its application in a diesel engine. This change allows the sensor to function effectively in this TOYOTA D-CAT type diesel engine, and it also avoids problems with sensor temperature and particulate matter (PM).
In order to reduce both PM and nitrogen oxides (NOx), the ECM adjusts the air-fuel ratio to a mixture that is slightly richer than that which would otherwise be used. (note that this mixture is still leaner than the stoichiometric air fuel ratio) The ECM bases these adjustments on signals that it receives from the A/F sensor.
When the ECM performs DPNR catalyst regeneration (cleaning) by adding fuel using the exhaust fuel addition injector, the A/F sensor feedback is used to ensure that an appropriate air fuel ratio is maintained.
*1: This voltage change occurs only inside the computer. It is not possible to measure this voltage at the sensor. The intelligent tester can be used to monitor this voltage.
- HINT:
- The ECM provides a pulse width modulated control circuit to adjust current through the heater. The A/F sensor heater circuit uses a relay on the B+ side of the circuit.
| DTC No. | DTC Detection Condition | Trouble Area |
| P0031 | A/F sensor heater current is 0.8 A or less when the heater operates (1 trip detection logic) |
Open in A/F sensor heater circuit A/F sensor heater A/F relay ECM |
| P0032 | A/F sensor heater current is 10.4 A or more when the heater operates A/F sensor heater current is 0.8 A or more when the heater not operating (1 trip detection logic) |
Short in A/F sensor heater circuit A/F sensor heater A/F relay ECM |
MONITOR DESCRIPTION
The inner surface of the A/F sensor element is exposed to outside air. The outer surface of the sensor element is exposed to exhaust gases. 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 of the exhaust and the outside air. The platinum coating amplifies the voltage generation. When heated, the sensor becomes very efficient. If the temperature of the exhaust is low, the sensor will not generate useful voltage signals without supplemental heating. The ECM regulates the supplemental heating by using a duty-cycle approach to regulate the average current in the heater element. If the heater current is out of the normal range, the sensor's output signals will be inaccurate and the ECM can not regulate the air-fuel ratio properly. When the heater current is out of the normal operating range, the ECM interprets this as a malfunction and sets a DTC.
WIRING DIAGRAM
INSPECTION PROCEDURE
| 1.INSPECT AIR FUEL RATIO SENSOR (HEATER RESISTANCE) |
Disconnect the P35 A/F sensor connector.
Measure the resistance between the terminals of the A/F sensor.
- Standard resistance:
Tester Connection Connection Specified Condition HAF2 (P35-1) - +B (2) 20°C (68°F) 1.8 to 3.4 Ω
Reconnect the A/F sensor connector.
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| NG | |
| 3.INSPECT AIR FUEL RATIO SENSOR RELAY |
Remove the A/F sensor relay.
Inspect the A/F sensor relay.
- Standard resistance:
Tester Connection Specified Condition 3 - 5 10 kΩ or higher Below 1 Ω
(Apply battery voltage to terminals 1 and 2)
Reinstall the A/F sensor relay.
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| OK | |
| 4.CHECK A/F FUSE |
Remove the A/F fuse from the engine room R/B No. 2.
Measure the resistance.
- Standard resistance:
- Below 1 Ω
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| OK | |
| 5.CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM, A/F SENSOR - A/F RELAY) |
Check the harness and connectors between the A/F sensor connector and the A/F relay.
Disconnect the P35 A/F sensor connector.
Remove the A/F relay from the engine room R/B No. 2.
Check the resistance between the wire harness side connectors.
- Standard resistance (Check for open):
Tester Connection Specified Condition +B (P35-2) - A/F relay (3) Below 1 Ω
- Standard resistance (Check for short):
Tester Connection Specified Condition +B (P35-2) or A/F relay (3) - Body ground 10 kΩ or higher
Reconnect the A/F sensor connector.
Reinstall the A/F relay.
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| OK | ||
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| 6.CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM) |
Check the harness and the connectors between the ECM and the A/F sensor.
Disconnect the P35 A/F sensor connector.
Disconnect the E59 ECM connector.
Check the resistance between the wire harness side connectors.
- Standard resistance (Check for open):
Tester Connection Specified Condition HAF2 (P35-1) - HAF2 (E59-104) Below 1 Ω
- Standard resistance (Check for short):
Tester Connection Specified Condition HAF2 (A35-1) or HAF2 (E59-104) - Body ground 10 kΩ or higher
Reconnect the A/F sensor connector.
Reconnect the ECM connector.
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| OK | ||
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