Toyota Tundra Service Manual: Cranking Holding Function Circuit

Toyota Tundra Service Manual / Engine, Hybrid System / 1ur-fe Engine Control / Sfi System / Cranking Holding Function Circuit

DESCRIPTION

The cranking holding control system keeps energizing the starter relay from when the ECM detects the starter signal (STSW signal) from the ignition switch until the ECM performs a judgment of "Engine started". Furthermore, the ECM outputs an accessory cut signal (ACCR signal) to the ACC cut relay during cranking to prevent flickering of the combination meter, clock, audio system, and so on.

When the ECM detects the STSW signal, the ECM outputs the starter relay drive signal (STAR signal) to the starter relay through the park/neutral position switch, and then, the engine is cranked. When the ECM receives a stable engine speed signal (NE signal), more specifically, when the NE signal reaches a predetermined value, the ECM stops outputting the STAR signal.

Also, the ECM monitors the starter relay operating conditions based on the STA terminal voltage status.

WIRING DIAGRAM

PROCEDURE

1.	READ VALUE USING TECHSTREAM (STARTER SIGNAL)

(a) Connect the Techstream to the DLC3.

(b) Turn the ignition switch to ON.

(d) Enter the following menus: Powertrain / Engine and ECT / Data List / Starter Signal.

(e) Check the result when the ignition switch is turned to the ON and START positions.

OK:

Ignition Switch Condition	Starter Signal
ON	OFF
START	ON

PROCEED TO NEXT CIRCUIT INSPECTION SHOWN IN PROBLEM SYMPTOMS TABLE

2.	INSPECT ECM (STSW TERMINAL VOLTAGE)

(a) Disconnect the ECM connector.

(b) Perform the cranking operation.

Standard Voltage:

Tester Connection	Ignition Switch Condition	Specified Condition
A24-14 (STSW) - Body ground	ON	Below 1 V
A24-14 (STSW) - Body ground	START	9 to 13 V

HINT:

DTCs related to the communication with other computers may be set due to this inspection. Clear those DTCs after the inspection.

GO TO STEP 7

3.	INSPECT ECM (STAR TERMINAL OUTPUT VOLTAGE)

(a) Connect the Techstream to the DLC3.

(b) Turn the ignition switch to ON.

(d) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the All Cylinders Fuel Cut.

(e) Measure the voltage according to the value(s) in the table below.

Standard Voltage:

Tester Connection	Switch Condition	Specified Condition
D73-6 (Junction Connector) - Body ground	Ignition switch ON (shift lever in P or N)	Below 1 V
	Ignition switch ON (shift lever not in P or N)	9 to 13 V
	Cranking operation	9 to 13 V

HINT:

The junction connector is in the engine room connector holder block as shown in the illustration.
During this inspection, all connectors and relays should be connected.

GO TO STEP 8

4.	INSPECT PARK/NEUTRAL POSITION SWITCH ASSEMBLY

(a) Inspect Park/Neutral Position (PNP) switch assembly.

for 2WD (See page )
for 4WD (See page )

REPLACE PARK/NEUTRAL POSITION SWITCH ASSEMBLY

5.	CHECK HARNESS AND CONNECTOR (PARK/NEUTRAL POSITIONSWITCH ASSEMBLY - ECM)

(a) Disconnect the park/neutral position (PNP) switch assembly connector.

(b) Disconnect the ECM connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
D35-4 (B) - D74-16 (STAR)	Always	Below 1 Ω
D35-4 (B) - D74-120 (NSW)	Always	Below 1 Ω

REPAIR OR REPLACE HARNESS OR CONNECTOR

6.	CHECK HARNESS AND CONNECTOR (PARK/NEUTRAL POSITION SWITCH ASSEMBLY - ECM - ST RELAY)

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

(b) Disconnect the park/neutral position (PNP) switch assembly switch connector.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
D35-5 (L) - A24-46 (STA)	Always	Below 1 Ω
D35-5 (L) - ST relay (2)	Always	Below 1 Ω
ST relay (1) - Body ground	Always	Below 1 Ω

REPAIR OR REPLACE STARTER CIRCUIT (STARTER - ST RELAY)

REPAIR OR REPLACE HARNESS OR CONNECTOR

7.	INSPECT IGNITION SWITCH ASSEMBLY

(a) Inspect the ignition switch assembly (See page ).

REPAIR OR REPLACE HARNESS OR CONNECTOR (IGNITION SWITCH ASSEMBLY - ECM)

REPLACE IGNITION SWITCH ASSEMBLY

8.	INSPECT PARK/NEUTRAL POSITION SWITCH ASSEMBLY

(a) Inspect Park/Neutral Position (PNP) switch assembly.

for 2WD (See page )
for 4WD (See page )

REPLACE PARK/NEUTRAL POSITION SWITCH ASSEMBLY

9.	CHECK HARNESS AND CONNECTOR (PARK/NEUTRAL POSITION SWITCH ASSEMBLY - IGNITION SWITCH ASSEMBLY AND ECM)

(a) Disconnect the ignition switch assembly connector.

(b) Disconnect the Park/Neutral Position (PNP) switch assembly connector.

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

Standard Resistance :

Tester Connection	Condition	Specified Condition
J9-7 (ST2) - D35-4 (B)	Always	Below 1 Ω
D74-16 (STAR) - D35-4 (B)	Always
D74-120 (NSW) - D35-4 (B)	Always
J9-7 (ST2) or D35-4 (B) - Body ground	Always	10 kΩ or higher
D74-16 (STAR) or D35-4 (B) - Body ground	Always
D74-120 (NSW) or D35-4 (B) - Body ground	Always

HINT:

The wire between the PNP switch and ignition switch has a diode (refer to the wiring diagram). The current flowing to the PNP switch is rectified by the diode.

REPAIR OR REPLACE HARNESS OR CONNECTOR

10.	CHECK HARNESS AND CONNECTOR (PARK/NEUTRAL POSITION SWITCH ASSEMBLY - ECM - ST RELAY)

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

(b) Disconnect the Park/Neutral Position (PNP) switch assembly connector.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
D35-5 (L) or A24-46 (STA) - Body ground	Always	10 kΩ or higher
D35-5 (L) or ST relay (2) - Body ground	Always	10 kΩ or higher

REPLACE ECM

REPAIR OR REPLACE HARNESS OR CONNECTOR

Checking Monitor Status

Data List / Active Test

See More:

Toyota Tundra Owners Manual > Using the driving support systems: Four-wheel drive system
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