Toyota Tundra Service Manual: 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.

(c) Turn the Techstream 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

OK

PROCEED TO NEXT CIRCUIT INSPECTION SHOWN IN PROBLEM SYMPTOMS TABLE

NG

2.

INSPECT ECM (STSW TERMINAL VOLTAGE)

(a) Disconnect the ECM connector.

(b) Perform the cranking operation.

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

Standard Voltage:

Tester Connection

Ignition Switch Condition

Specified Condition

A24-14 (STSW) - Body ground

ON

Below 1 V

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.

NG

GO TO STEP 7

OK

3.

INSPECT ECM (STAR TERMINAL OUTPUT VOLTAGE)

(a) Connect the Techstream to the DLC3.

(b) Turn the ignition switch to ON.

(c) Turn the Techstream 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.
NG

GO TO STEP 8

OK

4.

INSPECT PARK/NEUTRAL POSITION SWITCH ASSEMBLY

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

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

REPLACE PARK/NEUTRAL POSITION SWITCH ASSEMBLY

OK

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.

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

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

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

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.

(c) Disconnect the ECM 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

OK

REPAIR OR REPLACE STARTER CIRCUIT (STARTER - ST RELAY)

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

7.

INSPECT IGNITION SWITCH ASSEMBLY

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

OK

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

NG

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 )
NG

REPLACE PARK/NEUTRAL POSITION SWITCH ASSEMBLY

OK

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.

(c) Disconnect the ECM 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.

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

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.

(c) Disconnect the ECM 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

OK

REPLACE ECM

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

    Checking Monitor Status

    Data List / Active Test

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