Isuzu KB P190. Manual - part 269

6E-42  Engine Control System (4JH1) 

Scan Tool Does Not Communicate with Keyword 2000 Device 

Circuit Description 
The engine control module (ECM), transmission control
module (TCM) and anti-theft (keyless entry) control unit
(ACU) all communicate with the scan tool over the 
Keyword 2000 serial data link. However, the ECM and
fuel injection pump control unit (PCU) communicates
with each other over the controller area network (CAN)
link. The CAN link is not used for communication with
the scan tool and is shared only between the ECM and
PCU. 
Diagnostic Aids 
The following conditions will cause a loss of Keyword 
2000 serial data communication between the TCM and 
EHCU or between the scan tool and any control module:

 

 

 
•  A Keyword 2000 serial data circuit open. 
• A Keyword 2000 serial data circuit shorted to

ground. 

• A Keyword 2000 serial data circuit shorted to 

voltage. 

•  An internal condition within a module or connector 

on the Keyword 2000 serial data circuit, that causes 
a short to voltage or ground to the Keyword 2000 
serial data circuit. 

•  Open ground circuit (pin 5) at the DLC. 

 
Scan tool 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 scan tool. 
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) (A/T 

only) 

•  Electronic hydraulic control unit (EHCU) 

Does the scan tool communicate with all the listed 
control modules? 

 

Go to Step 3 

Go to Step 8 

3 

Does the scan tool communicate with the ECM? 

 

Go to Step 4 

Go to Lost 

Communication with 

The ECM 

4 

Does the scan tool communicate with the TCM? 

 

Go to Step 5 

Go to Diagnostic 

System Check 

Transmission 

Control 

5 

Does the scan tool communicate with the EHCU? 

 

Go to Step 6 

Go to Diagnostic 

System Brake 

6 

Test the Keyword 2000 serial data circuit for an 
intermittently short to ground or intermittently short to 
voltage. Then, test the Keyword 2000 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 

Test the data link connector (DLC) ground circuit at 
terminal 5 for an open circuit or poor connection. 
Did you find and correct the condition? 

 

Go to Step 15 

Go to Step 8 

Engine Control System (4JH1)  6E-43 

Step Action 

Value(s) 

Yes 

No 

8 

1.  Turn OFF the ignition. 
2. Disconnect the ECM C-56 and C-57 harness 

connectors. 

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

EHCU. 

Does the scan tool communicate with the TCM and 
EHCU? 

 

Go to Step 12 

Go to Step 9 

9 

1.  Turn OFF the ignition. 
2. Reconnect the ECM C-56 and C-57 harness 

connectors. 

3. Disconnect the TCM A and B harness 

connectors. 

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

EHCU. 

Does the scan tool communicate with the ECM and 
EHCU? 

 

Go to Step 13 

Go to Step 10 

10 

1.  Turn OFF the ignition. 
2. Reconnect the TCM A and B harness 

connectors. 

3.  Disconnect the EHCU C-67 harness connectors. 
4.  Turn ON the ignition, with the engine OFF. 
5.  Attempt to communicate with the ECM and TCM.
Does the scan tool communicate with the ECM and 
TCM? 

 

Go to Step 14 

Go to Step 11 

11 

Repair the short to ground or short to voltage on the 
Keyword 2000 serial data circuit between the DLC 
and ECM, TCM and EHCU. 
Did you complete the repair? 

 

Go to Step 15 

 

12 

Important: Replacement ECM must be 
programmed. 
Replace the ECM. Refer to Engine Control Module 
(ECM) Replacement in this section. 
Did you complete the replacement? 

 

Go to Step 15 

 

13 

Important: Replacement TCM must be 
programmed. 
Replace the TCM. Refer to Transmission Control 
Module (TCM) Replacement in the transmission 
section. 
Did you complete the replacement? 

 

Go to Step 15 

 

14 

Replace the EHCU. Refer to Electronic Hydraulic 
Control Unit in the anti-lock brake system section. 
Did you complete the replacement? 

 

Go to Step 15 

 

15 

Attempt to communicate with the ECM, TCM and 
EHCU. 
Does the scan tool communicate with the ECM, TCM 
and EHCU? 

 

System OK 

Go to Step 2 

 

6E-44  Engine Control System (4JH1) 

Lost Communication with The Engine Control Module (ECM) 

Circuit Description 
The engine control module (ECM), transmission control
module (TCM) and electronic hydraulic control unit
(EHCU) all communicate with the scan tool over the 
Keyword 2000 serial data link. However, the ECM and
fuel injection pump control unit (PCU) communicates
with each other over the controller area network (CAN) 
link. The CAN link is not used for communication with
the scan tool and is shared only between the ECM and
PCU. 

 

 
 
Lost Communication with The Engine Control
Module (ECM) 
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 

Attempt to establish engine control module (ECM) 
communications with the scan tool. 
Does the ECM communicate with the scan tool? 

 

Go to Intermittent 

Conditions 

Go to Step 3 

3 

Check the ECM C-56 and C-57 connectors for poor 
connections. 
Did you find and correct the condition? 

 

Go to Step 17 

Go to Step 4 

4 Check 

the 

electronic hydraulic

 control unit (EHCU) 

C-67 connector for poor connection. 
Did you find and correct the condition? 

 

Go to Step 17 

Go to Step 5 

5 

1.  Turn ON the ignition, with the engine OFF. 
2.  Check the ECM (30A) (SFB-4), ECM (10A) fuse 

(EB-4) and Engine (15A) fuse (C-6).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 ECM C-56 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 (pin 39 of C-56 connector). 

Does the test lamp illuminate? 

 

Go to Step 6 

Go to Step 14 

6 

1.  Turn OFF the ignition. 
2. Connect a DMM between the Keyword 2000 

serial data circuit at the ECM (pin 35 of C-56 
connector) and the EHCU (pin 11 of C-67 
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 17 

Go to Step 7 

7 

1.  Turn OFF the ignition. 
2. Connect a DMM between the Keyword 2000 

serial data circuit at the EHCU (pin 11 of C-67 
connector) and the DLC (pin 7 of B-58 
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 17 

Go to Step 8 

Engine Control System (4JH1)  6E-45 

Step Action 

Value(s) 

Yes 

No 

8 

Important: An open in a ground circuit at the ECM 
will not cause a loss of communication. 
1.  Check ECM ground for corrosion and tightness. 
2.  Clean or tighten grounds as necessary. 
Did you find and correct the condition? 

 

Go to Step 17 

Go to Step 9 

9 

1.  Turn OFF the ignition. 
2. Reconnect the ECM harness connector if 

previously disconnected. 

3.  Turn ON the ignition, with the engine OFF. 
4.  Replace the ECM main relay with the tail relay or 

replace with a known good relay. 

5.  Attempt to establish scan tool communications 

with the ECM. 

Does the ECM communicate with the scan tool? 

 

Go to Step 15 

Go to Step 10 

10 

1.  Turn OFF the ignition. 
2.  Remove the ECM main relay. 
3.  Turn ON the ignition, with the engine OFF. 
4.  Using a test lamp, check for battery voltage at 

both of the battery voltage supply circuits to the 
ECM main relay (pins 2 and 5 of X-12 
connector). 

5.  Repair the open in the circuit(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 17 

Go to Step 11 

11 

1.  Reinstall the ECM main relay. 
2.  Turn the ignition ON and OFF while listening or 

feeling for the ECM main relay click. Wait 2 
seconds between transitions. 

Does the ECM main relay click when the ignition is 
turned ON or OFF? 

 

Go to Step 13 

Go to Step 12 

12 

Repair the ECM main relay control circuit between 
the ECM main relay (pin 4 of X-12 connector) and 
the ECM (pin 58 of C-56 connector) for the following 
conditions: 

•  An open circuit 
•  A short to battery or ignition voltage 
•  High resistance or a poor connection at 

both the ECM and ECM main relay 

Did you find and correct the condition? 

 

Go to Step 17 

Go to Step 16 

13 

1.  Check ECM main relay voltage supply circuit to 

the ECM between the ECM main relay (pin 1 of 
X-12 connector) and the ECM (pin 3 of C-56 
connector) for the following conditions: 

•  An open circuit 
•  High resistance or a poor connection at the 

ECM and ECM main relay 

2.  Repair the circuit(s) as necessary. 
Did you find and correct the condition? 

 

Go to Step 17 

Go to Step 16 

14 

Repair the open in the ignition voltage circuit to the 
ECM. 
Did you complete the repair? 

 

Go to Step 17 

 

15 

Replace the ECM main relay. 
Did you complete the replacement? 

 

Go to Step 17 

 

16 

Important: Replacement ECM must be 
programmed. 
Replace the ECM. Refer to Engine Control Module 
(ECM) Replacement in this section. 
Did you complete the replacement? 

 

Go to Step 17 

