Isuzu N-Series. Manual - part 658

6E-54    Engine Control System (4HK1) 

14

1.

Review the following symptoms.

2.

Refer to the applicable symptom diagnostic
table:

• Hard Start
• Rough, Unstable, or Incorrect Idle and

Stalling

• High  Idle
• Cuts Out, Misses
• Surge / Chuggles
• Lack of Power, Sluggishness, or

Sponginess

• Hesitation, Sag, Stumble
• Fuel Knock / Combustion Noise
• Poor Fuel Economy
• Excessive Smoke (Black Smoke)
• Excessive Smoke (White Smoke)

Did you find and correct the condition?

—

System OK

Go to Intermittent 

Conditions

Step

Action

Value(s)

Yes

No

 Engine Control System (4HK1)    6E-55

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. The hill start aid
(HSA) control module communicates with the Keyword
82 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 TCM, SRS
control module and HSA 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 2000
Device
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views

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 – 

Engine Controls

2

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)

(Smoother only)

• Hill start aid (HSA) control module (If so

equipped)

• 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 8

3

Does the Tech 2 communicate with the ECM?

—

Go to Step 4

Go to Lost 

Communication with 

The ECM

4

Does the Tech 2 communicate with the TCM?

—

Go to Step 5

Go to Diagnostic 

System Check – 

Transmission 

Controls

5

Does the Tech 2 communicate with the HSA control
module?

—

Go to Step 6

Go to Diagnostic 

System Check – 

HSA Controls

6

Does the Tech 2 communicate with the SRS control
module?

—

Go to Step 7

Go to Diagnostic 

System Check – 

SRS Controls

7

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 17

System OK

6E-56    Engine Control System (4HK1) 

8

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, HSA
control module and SRS control module.

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

—

Go to Step 13

Go to Step 9

9

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, HSA
control module and SRS control module.

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

—

Go to Step 14

Go to Step 10

10

1.

Turn OFF the ignition.

2.

Reconnect the TCM B-425, B-426, B-427 and
B-428 harness connectors.

3.

Disconnect the HSA control module B-285
harness connectors.

4.

Turn ON the ignition, with the engine OFF.

5.

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

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

—

Go to Step 15

Go to Step 11

11

1.

Turn OFF the ignition.

2.

Reconnect the HSA control module B-285
harness connectors.

3.

Disconnect the SRS B-243 control module
harness connector.

4.

Turn ON the ignition, with the engine OFF.

5.

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

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

—

Go to Step 16

Go to Step 12

12

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

Did you complete the repair?

—

Go to Step 17

—

13

Important:
Replacement ECM must be programmed.

Replace the ECM. Refer to Engine Control Module
(ECM) Replacement / Fuel Injector ID Code Data
Programming in this section.

Did you complete the replacement?

—

Go to Step 17

—

Step

Action

Value(s)

Yes

No

 Engine Control System (4HK1)    6E-57

14

Replace the TCM. Refer to Transmission Control
Module (TCM) Replacement in the transmission
section.

Did you complete the replacement?

—

Go to Step 17

—

15

Replace the HSA control module. Refer to Hill Start
Aid (HSA) Control Module Replacement in the
brake section.

Did you complete the replacement?

—

Go to Step 17

—

16

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 17

—

17

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

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

—

System OK

Go to Step 2

Step

Action

Value(s)

Yes

No