Isuzu KB P190. Manual - part 1078

7A2-28   TRANSMISSION CONTROL SYSTEM (JR405E)

Scan Tool Does Not Power Up

Circuit Description

The data link connector (DLC) is a standardized 16-
cavity connector. Connector design and location is
dictated by an industry wide standard, and is required
to provide the following:

• Scan tool power battery positive voltage at

terminal 16

• Scan tool power ground at terminal 4

• Common signal ground at terminal 5

The scan tool will power up with the ignition OFF. Some
modules however, will not communicate unless the
ignition is ON.
Schematic Reference: Transmission Controls
Schematics
Connector End View Reference: Transmission
Controls Connector End Views or TCM Connector End
Views

Circuit/ System Testing Scan Tool Does Not Power Up

Step

Action

Value(s)

Yes

No

1

Important: Make sure the scan tool works properly
on another vehicle before using this chart.

1.

Turn OFF the ignition.

2.

Inspect the Meter (+B) (10A) fuse in the cabin
fuse block.

Is the Meter (+B) (10A) fuse open?

—

Go to Step 2 

Go to Step 3

2

Replace the Meter (+B) (10A) fuse. If the fuse
continues to open, repair the short to ground on
one of the circuits that is fed by the Meter (+B)
(10A) fuse or replace the shorted attached
component.

Did you complete the repair?

—

Go to Step 7

—

3

1.

Check each circuit at the data link connector
(DLC) (B-58) for a backed out, spread or
missing terminal.

2.

Repair the terminal as necessary.

Did you find and complete the repair?

—

Go to Step 7

Go to Step 4

4

Connect a test lamp between the +B circuit (pin 16
of B-58) at the DLC and a known good ground.

Does the test lamp illuminate?

—

Go to Step 6 

Go to Step 5

5

Repair the open in the battery voltage circuit to the
DLC.

Did you complete the repair?

—

Go to Step 7

—

6

1.

Test each ground circuit at the DLC (pins 4
and 5 of B-58) for an open circuit or high
resistance.

2.

Repair the circuit(s), clean or tighten ground
as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Intermittent 

Conditions

7

1.

Connect the scan tool to the DLC.

2.

Attempt to turn ON the scan tool.

Does the scan tool ON?

—

System OK 

Go to Step 1

TRANSMISSION CONTROL SYSTEM (JR405E)   7A2-29

Scan Tool Does Not Communicate with Keyword Device

Circuit Description

The TCM, electronic hydraulic control unit (EHCU)
[ABS module] and supplemental restraint system
(SRS) control module all communicate with the scan
tool over the Keyword serial data link. 

Diagnostic Aids

The following conditions will cause a loss of Keyword
serial data communication between the scan tool and
the TCM.

• A Keyword serial data circuit open

• A Keyword serial data circuit shorted to ground

• A Keyword serial data circuit shorted to voltage

• An internal condition within a module or connector

on the Keyword serial data circuit, that causes a
short to voltage or ground to the Keyword serial
data circuit

Schematic Reference: Transmission Controls
Schematics
Connector End View Reference: Transmission
Controls Connector End Views or TCM Connector End
Views

Circuit/ System Testing Scan Tool Does Not Communicate with Keyward Device

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check -
Engine Controls?

—

Go to Step 2

Go to Diagnostic 

System Check - 

Transmission 

Controls

2

1.

Install a scan tool. 

2.

Turn ON the ignition, with the engine OFF.

3.

Attempt to establish communication with the
listed control modules.

• TCM

• Electronic hydraulic control unit (EHCU)

[ABS module] (If so equipped)

• Supplemental restraint system (SRS)

control module (If so equipped)

Does the scan tool communicate with any of the
listed control modules?

—

Go to Step 3 

Go to Step 7

3

Does the scan tool communicate with the TCM?

—

Go to Step 4

Go to Lost 

Communication with

The Transmission 

Control Module 

(TCM)

4

Notice: If no ABS is installed, skip to Step 5.

Does the scan tool communicate with the EHCU?

—

Go to Step 5

Go to Diagnostic 

System Check - 

Anti-lock Brake 

Controls

5

Notice: If no SRS is installed, skip to Step 6.

Does the scan tool communicate with the SRS
control module?

—

Go to Step 6

Go to Diagnostic 

System Check -SRS 

Controls

6

Test the Keyword serial data circuit for an
intermittently short to ground or intermittently short
to voltage. Then, test the Keyword serial data
circuit for an intermittently open (based on which
control module did not communicate) at the
connection in the circuit.

Did you find and correct the condition?

—

Go to Step 15

System OK

7

1.

Inspect for an intermittent, for a poor
connection and for corrosion at the data link
connector (DLC) (pin 7 of B-58). 

2.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 8

7A2-30   TRANSMISSION CONTROL SYSTEM (JR405E)

8

1.

Turn OFF the ignition.

2.

Disconnect the TCM C-94 and C-95 harness
connectors.

3.

Turn ON the ignition, with the engine OFF.

4.

Attempt to communicate with the EHCU and
SRS control module.

Does the scan tool communicate with the EHCU
and SRS control module?

—

Go to Step 12 

Go to Step 9

9

Notice: If no ABS is installed, skip to Step 10.

1.

Turn OFF the ignition. 

2.

Reconnect the TCM harness connectors. 

3.

Disconnect the EHCU harness connector.

4.

Turn ON the ignition, with the engine OFF.

5.

Attempt to communicate with the TCM and
SRS control module.

Does the scan tool communicate with the TCM and
SRS control module?

—

Go to Step 13

Go to Step 10

10

Notice: If no SRS is installed, skip to Step 11.

1.

Turn OFF the ignition.

2.

Reconnect the TCM harness connectors if
disconnected. 

3.

Reconnect the EHCU harness connector if
disconnected. 

4.

Disconnect the SRS control module harness
connector. 

5.

Turn ON the ignition, with the engine OFF.

6.

Attempt to communicate with the TCM and
EHCU.

Does the scan tool communicate with the TCM and
EHCU?

—

Go to Step 14

Go to Step 11

11

Repair the short to ground or short to voltage on
the Keyword serial data circuit between the DLC
and TCM, EHCU and SRS control module.

Did you complete the repair?

—

Go to Step 15

—

12

Important: Replacement TCM must be
programmed.
Replace the TCM. Refer to TCM Replacement.

Did you complete the replacement?

—

Go to Step 15

—

13

Replace the EHCU. Refer to EHCU Replacement.

Did you complete the replacement?

—

Go to Step 15

—

14

Replace the SRS control module. Refer to SRS
Control Module Replacement.

Did you complete the replacement?

—

Go to Step 15

—

15

Attempt to establish communication with the TCM,
EHCU and SRS control module.

Does the scan tool communicate with the TCM,
EHCU and SRS control module? 

—

System OK 

Go to Step 2

Step

Action

Value(s)

Yes

No

TRANSMISSION CONTROL SYSTEM (JR405E)   7A2-31

Lost Communication with The Transmission Control Module (TCM)

Circuit Description

The TCM, electronic hydraulic control unit (EHCU)
[ABS module] and supplemental restraint system
(SRS) control module all communicate with the scan
tool over the Keyword serial data link. 

Schematic Reference: Transmission Controls
Schematics
Connector End View Reference: Transmission
Controls Connector End Views or TCM Connector End
Views

Circuit/ System Testing Lost Communication with The Transmission Control Module (TCM)

Step

Action

Action

Yes

No

1

Did you perform the Diagnostic System Check -
Engine Controls?

—

Go to Step 2

Go to Diagnostic 

System Check - 

Transmission 

Controls

2

Attempt to establish communication with the TCM.

Does the scan tool communicate with the TCM?

—

Go to Intermittent 

Conditions 

Go to Step 3

3

1.

Inspect for an intermittent, for poor
connections and for corrosion at the TCM C-
94 and C-95 harness connectors.

2.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 4

4

1.

Check the TCM (15A) in the cabin fuse block.
Replace and retest if open. If any fuse
continues to open, repair the short to ground
on each circuit fed by that fuse.

2.

Turn OFF the ignition.

3.

Disconnect the TCM C-95 harness connector.

4.

Turn ON the ignition, with the engine OFF.

5.

Connect a test lamp to ground and check for
voltage at the ignition voltage supply circuit at
the TCM (pins 18 and 24 of C-95).

Does the test lamp illuminate?

—

Go to Step 6

Go to Step 5

5

Repair the open in the ignition voltage circuit to the
TCM.

Did you complete the repair?

—

Go to Step 9

—

6

1.

Turn OFF the ignition.

2.

Disconnect the TCM C-94 harness connector.

3.

Inspect for an intermittent, for poor
connections and corrosion at the harness
connector of the TCM (pin 5 of C-94).

4.

Test the Keyword serial data circuit between
the TCM (pin 5 of C-94) and the DLC (pin 7 of
B-58) for an open circuit or high resistance.

5.

Repair the connection(s) or circuit(s) as
necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 7

7

1.

Check TCM ground for corrosion and
tightness.

2.

Clean or tighten grounds as necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 8