3UR-FE ENGINE CONTROL: SFI SYSTEM: DESCRIPTION (2008 Sequoia)

Last Modified: 11-29-2007		1.6 C
Service Category: Engine/Hybrid System	Section: Engine Control
Model Year: 2008	Model: Sequoia	Doc ID: RM000000WC1066X
Title: 3UR-FE ENGINE CONTROL: SFI SYSTEM: DESCRIPTION (2008 Sequoia)

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)

DTC

P0051

Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1)

DTC

P0052

Oxygen (A/F) Sensor Heater Control Circuit High (Bank 2 Sensor 1)

DESCRIPTION

Refer to DTC P2195 .

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.
When one of these DTCs is stored, the ECM enters fail-safe mode. The ECM turns off the A/F 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 A/F sensor heater circuit uses a relay on the +B side of the circuit.

DTC No.

DTC Detection Condition

Trouble Area

P0031

P0051

Air-Fuel Ratio (A/F) sensor heater current less than 0.8 A

(1 trip detection logic)

Open in A/F sensor heater circuit
A/F sensor heater (for Sensor 1)
Integration relay
ECM

P0032

P0052

Air-Fuel Ratio (A/F) sensor heater current failure

(1 trip detection logic)

Short in A/F sensor heater circuit
A/F sensor heater (for Sensor 1)
Integration relay
ECM

HINT:

Bank 1 refers to the bank that includes No. 1 cylinder.
Bank 2 refers to the bank that does not include No. 1 cylinder.
Sensor 1 refers to the sensor closest to the engine assembly.
Sensor 2 refers to the sensor farthest away from the engine assembly.

MONITOR DESCRIPTION

The ECM 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 purify 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 the 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 stores a DTC.

Example:

The ECM stores DTC P0032 or P0052 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 or P0051 is stored.

MONITOR STRATEGY

Related DTCs	P0031: A/F sensor heater (for Bank 1) open/short (Low electrical current) P0032: A/F sensor heater (for Bank 1) open/short (High electrical current) P0051: A/F sensor heater (for Bank 2) open/short (Low electrical current) P0052: A/F sensor heater (for Bank 2) open/short (High electrical current)
Required Sensors/Components (Main)	A/F sensor heater
Required Sensors/Components (Related)	-
Frequency of Operation	Continuous
Duration	10 seconds
MIL Operation	Immediate
Sequence of Operation	None

TYPICAL ENABLING CONDITIONS

All

Monitor runs whenever following DTCs not present	None
Battery voltage	Less than 20 V
Engine	Running
When either condition below is met:	Condition A or B
Condition A:	-
Heater output duty	More than 0%
Condition B:	-
When all conditions below are met:	-
Battery voltage	10.5 V or more
Time after engine start	10 seconds or more
A/F sensor heater duty-cycle ratio	50% or more

TYPICAL MALFUNCTION THRESHOLDS

P0031 and P0051

A/F sensor heater current

Less than 0.8 A

P0032 and P0052

Hybrid IC high current limiter port

Fail

COMPONENT OPERATING RANGE

A/F sensor heater current

0.9 to 9.9 A

WIRING DIAGRAM

Refer to DTC P2195 .

INSPECTION PROCEDURE

HINT:

Read freeze frame data using the Techstream. Freeze frame data records the engine condition when malfunctions are detected. 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 A/F sensor connector.

(b) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection	Condition	Specified Condition
1 (HA1A) - 2 (+B)	20°C (68°F)	1.8 to 3.4 Ω
1 (HA1A) - 4 (A1A-)	Always	10 kΩ or higher
1 (HA2A) - 2 (+B)	20°C (68°F)	1.8 to 3.4 Ω
1 (HA2A) - 4 (A2A-)	Always	10 kΩ or higher

2.	CHECK TERMINAL VOLTAGE (+B OF A/F SENSOR)

(a) Disconnect the A/F sensor connector.

(b) Turn the ignition switch to ON.

Standard Voltage:

Tester Connection	Switch Condition	Specified Condition
D19-2 (+B) - Body ground	Ignition switch ON	11 to 14 V
D20-2 (+B) - Body ground	Ignition switch ON	11 to 14 V

Result

Result	Proceed to
NG	A
OK	B

3.	INSPECT INTEGRATION RELAY (A/F)

(a) Remove the integration relay from the engine room relay block.

(b) Inspect the A/F fuse.

(1) Remove the A/F fuse from the integration relay.

(2) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection	Condition	Specified Condition
A/F fuse	Always	Below 1 Ω

(3) Reinstall the A/F fuse.

(1) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection	Condition	Specified Condition
1C-1 - 1A-4	When no battery voltage applied to terminals 1A-2 and 1A-3	10 kΩ or higher
1C-1 - 1A-4	When battery voltage applied to terminals 1A-2 and 1A-3	Below 1 Ω

4.	CHECK HARNESS AND CONNECTOR (INTEGRATION RELAY - A/F SENSOR AND BODY GROUND)

(a) Disconnect the A/F sensor connector.

(b) Remove the integration relay from the engine room relay block.

Standard Resistance:

Tester Connection	Condition	Specified Condition
D19-2 (+B) - 1A-4	Always	Below 1 Ω
D20-2 (+B) - 1A-4	Always	Below 1 Ω
1A-2 - 1B-5	Always	Below 1 Ω
1A-3 - Body ground	Always	Below 1 Ω
D19-2 (+B) or 1A-4 - Body ground	Always	10 kΩ or higher
D20-2 (+B) or 1A-4 - Body ground	Always	10 kΩ or higher
1A-2 or 1B-5 - Body ground	Always	10 kΩ or higher

9.	CHECK HARNESS AND CONNECTOR (A/F SENSOR - ECM)

(a) Disconnect the A/F sensor connector.

(b) Disconnect the ECM connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
D19-1 (HA1A) - D56-22 (HA1A)	Always	Below 1 Ω
D20-1 (HA2A) - D56-20 (HA2A)	Always	Below 1 Ω
D19-1 (HA1A) or D56-22 (HA1A) - Body ground	Always	10 kΩ or higher
D20-1 (HA2A) or D56-20 (HA2A) - Body ground	Always	10 kΩ or higher

10.	CHECK WHETHER DTC OUTPUT RECURS

(a) Connect the Techstream to the DLC3.

(b) Turn the ignition switch to ON.

(d) Clear DTCs .

(e) Start the engine.

(f) Allow the engine to idle for 1 minute or more.

(g) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

(h) Read DTCs.

Result

Result	Proceed to
No DTC is output	A
P0031, P0032, P0051 or P0052 is output	B