Isuzu 4JA1 Workshop Manual page 298

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.
Step
1 Did you perform the 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?
3 Check the ECM C-56 and C-57 connectors for poor
connections.
Did you find and correct the condition?
electronic hydraulic
4 Check the
C-67 connector for poor connection.
Did you find and correct the condition?
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 36 of C-56 connector).
Does the test lamp illuminate?
6 1. Turn OFF the ignition.
2. Connect a DMM between the Keyword 2000
serial data circuit at the ECM (pin 32 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?
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?
Action
control unit (EHCU)
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
Value(s) Yes

Go to Step 2

Go to Intermittent
Conditions

Go to Step 17

Go to Step 17
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Go to Step 6

Go to Step 17
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Go to Step 17
No
Go to Diagnostic
System Check-
Engine Controls
Go to Step 3
Go to Step 4
Go to Step 5
Go to Step 14
Go to Step 7
Go to Step 8