Isuzu N-Series. Service manual - part 924

Transmission Control System (Smoother) 7A-151

5

1. Connect a test lamp between the ground

circuit of the 1-3-5 shift solenoid valve harness
(pin 1 of J-235 connector) and battery voltage.

2. Turn ON the ignition.

Does the test lamp illuminate?

—

Go to Step 9

Go to Step 8 

6

1. Test the voltage feed circuit between the

transmission control module (TCM) (pins 4
and 5 of B-425 connector) and the gearshift
control box relay (pin 2 of X-19 connector) for
an open circuit or high resistance.

2. Test the control circuit between the TCM (pins

21 and 31 of B-425 connector) and the 1-3-5
shift solenoid (pin 2 of J-235 connector) for an
open circuit or high resistance.

3. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 10

7

Important:
The 1-3-5 shift solenoid valve may be damaged if
the solenoid valve control circuit is shorted to a
voltage source.

1. Test the control circuit between the TCM (pins

21 and 31 of B-425 connector) and the 1-3-5
shift solenoid (pin 2 of J-235 connector) for a
short to battery or ignition voltage.

2. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

8

1. Test the ground circuit between the 1-3-5 shift

solenoid (pin 1 of J-235 connector) and
chassis ground (J-9) for an open circuit or high
resistance.

2. Test the ground circuit between the TCM (pins

6 and 7 of B-425 connector) and chassis
ground (J-9) for an open circuit or high
resistance.

3. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 10 

9

1. Turn OFF the ignition.
2. Disconnect the 1-3-5 shift solenoid valve

harness connector.

3. Inspect for an intermittent and for poor

connections at the harness connector of the 1-
3-5 shift solenoid valve (pins 1 and 2 of J-235
connector).

4. Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 11

10

1. Turn OFF the ignition.
2. Disconnect the TCM harness connector.
3. Inspect for an intermittent and for poor

connections on the 1-3-5 shift solenoid circuits
at the harness connector of the TCM (pins 4,
5, 6, 7, 21 and 31 of B-425 connector).

4. Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

Step

Action

Value(s)

Yes

No

7A-152 Transmission Control System (Smoother)

11

Important:
Replacement 1-3-5 shift solenoid valve must be
relearned. 
Replace the 1-3-5 shift solenoid valve. Refer to
Repair Instructions (Overhaul) - Gearshift Control
Box in this section. 

Did you complete the replacement?

—

Go to Step 13

—

12

Important:
Replacement TCM must be programmed and
learned.
Replace the TCM. Refer to Transmission Control
Module (TCM) Replacement in this section.

Did you complete the replacement?

—

Go to Step 13

—

13

1. Reconnect all previously disconnected

harness connector(s).

2. Clear the DTCs with the Tech 2.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine.
5. Operate the vehicle within the Conditions for

Running the DTC. 

Did the DTC fail this ignition?

—

Go to Step 2

Go to Step 14

14

Observe the DTC Information with the Tech 2. 

Are there any DTCs that you have not diagnosed?

—

Go to Diagnostic 

Trouble Code (DTC) 

List

System OK

Step

Action

Value(s)

Yes

No

Transmission Control System (Smoother) 7A-153

P0977 (Flash Code 73)

Circuit Description
The pulse width modulation (PWM) 1-3-5 shift solenoid
valve is located on the gearshift control box. The
transmission control module (TCM) controls the 1-3-5
shift solenoid valve by duty cycle signal based on
commanded gear position. The 1-3-5 shift solenoid is
commanded ON when the commanded gear is set to
1st, 3rd and 5th gear. When disengaging from 2nd, 4th,
6th and reverse gear, the 1-3-5 shift solenoid is also
commanded ON. The gear shift position sensor is used
to detect the shift side lever position feedback for the
shift solenoid valves movement. The TCM uses the gear
shift position sensor to determine the current gear
position with a combination of the gear select position
sensor. If the TCM detects a low voltage condition on
the 1-3-5 shift solenoid valve monitor circuit when the
solenoid valve is commanded ON, this DTC will set.
Condition for Running the DTC

• DTC P0889 is not set.
• The ignition switch is ON.
• The ignition voltage is more than 20 volts.
• The emergency switch is OFF.
• The gearshift control box relay is commanded ON.

Condition for Setting the DTC

• The TCM detects a low voltage condition on the 1-

3-5 shift solenoid valve monitor circuit when the
solenoid valve is commanded ON.

Action Taken When the DTC Sets

• The TCM illuminates the transmission warning

lamp when the diagnostic runs and fails.

• The TCM intermittently sounds buzzer when the

diagnostic runs and fails. 

• The TCM commands OFF gearshift control box

relay.

• The TCM inhibits gearshift control and holds gear

position when the diagnostic runs and fails.

• The TCM inhibits gear select & shift position

learning and half-clutch learning.

Condition for Clearing the DTC

• The TCM turns OFF the transmission warning

lamp when the diagnostic runs and does not fail at
next ignition cycle

• The TCM stops the buzzer when the diagnostic

runs and does not fail at next ignition cycle.

• A current DTC clears when the diagnostic runs and

does not fail at next ignition cycle.

• A history DTC clears with the Tech 2 or reset

switch operation.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

DTC P0977 (Flash Code 73)

Schematic Reference: Transmission Controls
Schematics
Connector End View Reference: Transmission
Controls Connector End Views or Transmission Control
Module (TCM) Connector End Views

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check -
Transmission Controls?

—

Go to Step 2

Go to Diagnostic 

System Check - 

Transmission 

Controls

2

1. Install the Tech 2.
2. Turn OFF the ignition for 30 seconds.
3. Place the transmission in neutral and set the

parking brake.

4. Start the engine. 
5. Operate the selector lever from N to D and

from D to N in order to energize the 1-3-5 shift
solenoid valve.

6. Monitor the Diagnostic Trouble Code (DTC)

Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Diagnostic 

Aids

3

1. Turn OFF the ignition for 30 seconds.
2. Disconnect the 1-3-5 shift solenoid valve

harness connector.

3. Turn ON the ignition, with the engine OFF.
4. Monitor the DTC Information with the Tech 2.

Is DTC P0976 set?

—

Go to Step 5

Go to Step 4

7A-154 Transmission Control System (Smoother)

4

1. Test the control circuit between the

transmission control module (TCM) (pins 21
and 31 of B-425 connector) and the 1-3-5 shift
solenoid (pin 2 of J-235 connector) for a short
to ground. 

2. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Step 6

5

Important:
Replacement 1-3-5 shift solenoid valve must be
relearned. 
Replace the 1-3-5 shift solenoid valve. Refer to
Repair Instructions (Overhaul) - Gearshift Control
Box in this section. 

Did you complete the replacement?

—

Go to Step 7

—

6

Important:
Replacement TCM must be programmed and
learned.
Replace the TCM. Refer to Transmission Control
Module (TCM) Replacement in this section.

Did you complete the replacement?

—

Go to Step 7

—

7

1. Reconnect all previously disconnected

harness connector(s).

2. Clear the DTCs with the Tech 2.
3. Turn OFF the ignition for 30 seconds.
4. Place the transmission in neutral and set the

parking brake.

5. Start the engine. 
6. Operate the selector lever from N to D and

from D to N in order to energize the 1-3-5 shift
solenoid valve.

7. Monitor the DTC Information with the Tech 2.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 8

8

Observe the DTC Information with the Tech 2. 

Are there any DTCs that you have not diagnosed?

—

Go to Diagnostic 

Trouble Code (DTC) 

List

System OK

Step

Action

Value(s)

Yes

No