Isuzu N-Series. Manual - part 897

Transmission Control System (Smoother) 7A-43

Tech 2 Does Not Communicate with Keyword Device

Circuit Description
The engine control module (ECM), transmission control
module (TCM) and supplemental restraint system
(SRS) control module communicates with the Tech 2
over the Keyword 2000 serial data link. However, the
ECM, TCM, electric hydraulic control module (EHCU)
(ABS module) and the data recording module (DRM)
communicate with each other over the controller area
network (CAN) link. The CAN link is not used for
communication with the Tech 2 and is shared only
among each module.
Diagnostic Aids
The following conditions will cause a loss of Keyword
serial data communication between the ECM, TCM and
SRS control module or between the Tech 2 and any
control module:

• 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.

Tech 2 Does Not Communicate with Keyword
Device

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

Did you perform the Diagnostic System Check -
Transmission Controls?

—

Go to Step 2

Go to Diagnostic

System Check -

Transmission

Controls

1. Install the Tech 2.
2. Turn ON the ignition, with the engine OFF.
3. Attempt to communicate with the listed control

modules.

• Engine control module (ECM)
• Transmission control module (TCM)
• Supplemental restraint system (SRS)

control module (If so equipped)

Does the Tech 2 communicate with all the listed
control modules?

—

Go to Step 3

Go to Step 7

Does the Tech 2 communicate with the ECM?

—

Go to Step 4

Go to Diagnostic

System Check -

Engine Control

Does the Tech 2 communicate with the TCM?

—

Go to Step 5

Go to Lost

Communication with

The TCM

Does the Tech 2 communicate with the SRS control
module?

—

Go to Step 6

Go to Diagnostic

System Check -SRS

Control

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 14

System OK

1. Turn OFF the ignition.
2. Disconnect the ECM E-111 and J-191 harness

connectors.

3. Turn ON the ignition, with the engine OFF.
4. Attempt to communicate with the TCM and

SRS control module.

Does the Tech 2 communicate with the TCM and
SRS control module?

—

Go to Step 11

Go to Step 8

7A-44 Transmission Control System (Smoother)

1. Turn OFF the ignition.
2. Reconnect the ECM E-111 and J-191 harness

connectors.

3. Disconnect the TCM B-425, B-426, B-427 and

B-428 harness connectors.

4. Turn ON the ignition, with the engine OFF.
5. Attempt to communicate with the ECM and

SRS control module.

Does the Tech 2 communicate with the ECM and
SRS control module?

—

Go to Step 12

Go to Step 9

1. Turn OFF the ignition.
2. Reconnect the TCM B-425, B-426, B-427 and

B-428 harness connectors.

3. Disconnect the SRS B-243 control module

harness connector.

4. Turn ON the ignition leaving the engine OFF.
5. Attempt to communicate with the ECM and

TCM.

Does the Tech 2 communicate with the ECM and
TCM?

—

Go to Step 13

Go to Step 10

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

Did you complete the repair?

—

Go to Step 14

—

Important:

Replacement ECM must be programmed.
Replace the ECM. Refer to Engine Control Module
(ECM) Replacement /Restore Fuel Injector ID Code
Data in engine control section.

Did you complete the replacement?

—

Go to Step 14

—

Important:

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

Did you complete the replacement?

—

Go to Step 14

—

Replace the SRS control module. Refer to
Supplemental Restraint System (SRS) control
module Replacement in the restraint system
section.

Did you complete the replacement?

—

Go to Step 14

—

Attempt to communicate with the ECM, TCM and
SRS control module.

Does the Tech 2 communicate with the ECM, TCM
and SRS control module?

—

System OK

Go to Step 2

Step

Action

Value(s)

Yes

Transmission Control System (Smoother) 7A-45

Lost Communication with The Transmission Control Module (TCM)

Lost Communication with The Transmission
Control Module (TCM)

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

Did you perform the Diagnostic System Check -
Transmission Controls?

—

Go to Step 2

Go to Diagnostic

System Check -

Transmission

Controls

Attempt to establish transmission control module
(TCM) communications with the Tech 2.

Does the TCM communicate with the Tech 2?

—

Go to Intermittent

Conditions

Go to Step 3

Check the TCM B-425, B-426, B-427 and B-428
connectors for poor connections.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 4

1. Turn ON the ignition, with the engine OFF.
2. Check the NEES (IG) (10A) fuse (F-17) in the

glove box fuse block. Replace and retest if
open. If any fuse continues to open, check for
a short to ground on each circuit fed by that
fuse.

3. Turn OFF the ignition.
4. Disconnect the TCM B-426 harness

connector.

5. Turn ON the ignition, with the engine OFF.
6. Connect a test lamp to ground and check for

voltage at the ignition voltage supply circuit at
the ECM (pins 1 and 2 of B-426 connector).

Does the test lamp illuminate?

—

Go to Step 5

Go to Step 7

1. Turn OFF the ignition.
2. Connect a DMM between the Keyword serial

data circuit at the TCM (pin 9 of B-426
connector) and the data link connector (DLC)
(pin 7 of B-79 connector).

3. Test the circuits for an open circuit or high

resistance.

4. Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 6

Important:

An open in a ground circuit at the TCM will not cause
a loss of communication.

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

7A-46 Transmission Control System (Smoother)

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

Did you complete the repair?

—

Go to Step 9

—

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

Did you complete the replacement?

—

Go to Step 9

—

1. Turn OFF the ignition.
2. Reconnect all previously disconnected fuse or

harness connector(s).

3. Turn the ignition ON with the engine OFF.
4. Attempt to establish Tech 2 communications

with the ECM.

Does the Tech 2 communicate with the TCM?

—

System OK

Go to Step 3

Step

Action

Value(s)

Yes

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