Isuzu N-Series. Manual - part 716

6E-286    Engine Control System (4HK1) 

Chart for with Smoother and ABS

25

1.

Inspect for an intermittent, for poor
connections and corrosion on the CAN Low
and High circuits at the harness connector of
the ECM (pins 18 and 37 of J-191 connector).

2.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 31

Go to Step 30

26

Replace the resistor 1.

Did you complete the replacement?

—

Go to Step 31

—

27

Replace the resistor 2.

Did you complete the replacement?

—

Go to Step 31

—

28

Replace the DRM. Refer to Data Recording Module
(DRM) Replacement.

Did you complete the replacement?

—

Go to Step 31

—

29

Replace the EHCU. Refer to Electric Hydraulic
Control Unit (EHCU Replacement in the Anti-lock
Brake section).

Did you complete the replacement?

—

Go to Step 31

—

30

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 31

—

31

1.

Reconnect all previously disconnected
harness connector(s).

2.

Clear the DTCs with the Tech 2.

3.

Turn OFF the ignition for 30 seconds.

4.

Start the engine.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 32

32

Observe the DTC Information with the Tech 2.

Are there any DTCs that you have not diagnosed?

—

Go to Diagnostic 

Trouble Code (DTC) 

List

System OK

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 OFF the ignition for 30 seconds.

3.

Monitor the engine control module (ECM)
Diagnostic Trouble Code (DTC) Information
with the Tech 2.

4.

Start the engine.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Diagnostic 

Aids

3

Attempt to communicate with the transmission
control module (TCM) via the Transmission Data
table.

Does the Tech 2 communicate with the TCM?

—

Go to Step 4

Go to Diagnostic 

System Check – 

Transmission 

Controls

Step

Action

Value(s)

Yes

No

 Engine Control System (4HK1)    6E-287

4

Attempt to communicate with the electrical
hydraulic control unit (EHCU) (ABS module) via the
ABS Data table.

Does the Tech 2 communicate with the EHCU?

—

Go to Step 5

Go to Diagnostic 

System Check – 

Anti-lock Brake 

System Controls

5

1.

Turn OFF the ignition.

2.

Measure the resistance across the controller
area network (CAN) Low and High circuits by
back probing the resistor 1 (pins 1 and 2 of B-
387 connector) (resistor 1 is located near the
driver’s side dash panel. It is blue connector).

Is the resistance within the specified value (parallel
resistance of the 120 

Ω resister 1 and the 120 Ω

resistor 2 should be 60 

Ω)?

50 – 70 

Ω

Go to Step 14

Go to Step 6

6

Is the resistance less than the specified value at
Step 5?

—

Go to Step 7

Go to Step 12

7

1.

Keep the DMM with connected.

2.

Disconnect the EHCU harness connector.

Is the resistance within the specified value?

110 – 130 

Ω

Go to Step 9

Go to Step 8

8

1.

Keep the DMM with connected.

2.

Disconnect the TCM harness connectors.

Is the resistance within the specified value?

110 – 130 

Ω

Go to Step 35

Go to Step 25

9

Measure the resistance across the CAN Low and
High circuits by back probing the resistor 2 (pins 1
and 2 of B-431 connector) (resistor 2 is located
behind the radio and above the heater unit. It is
blue connector).

Is the resistance within the specified value?

110 – 130 

Ω

Go to Step 36

Go to Step 10

10

1.

Keep the DMM with connected.

2.

Disconnect the engine control module (ECM)
harness connectors.

Is the resistance within the specified value?

110 – 130 

Ω

Go to Step 37

Go to Step 11

11

1.

Keep the DMM with connected.

2.

Disconnect the data recording module (DRM)
harness connector (DRM is located behind the
glove box).

Is the resistance within the specified value?

110 – 130 

Ω

Go to Step 34

Go to Step 26

12

1.

Disconnect the resistor 1 harness connector.

2.

Measure the resistance of the resistor 1.

Is the resistance within the specified value?

110 – 130 

Ω

Go to Step 13

Go to Step 32

13

1.

Disconnect the resister 2 harness connector
(resistor 2 is located behind the radio and
above the heater unit. It is blue connector).

2.

Measure the resistance of the resistor 2.

Is the resistance within the specified value?

110 – 130 

Ω

Go to Step 27

Go to Step 33

Step

Action

Value(s)

Yes

No

6E-288    Engine Control System (4HK1) 

14

1.

Disconnect the resistor 1 and resistor 2
harness connector.

2.

Turn ON the ignition, with the engine OFF.

3.

Connect a DMM between the CAN Low circuit
(pin 1 of B-387 connector) and a known good
ground at the resistor 1 harness connector.
Record the voltage reading.

4.

Connect a DMM between the CAN High circuit
(pin 2 of B-387 connector) and a known good
ground at the resistor 1 harness connector.
Record the voltage reading.

Are both voltage readings within the specified
value?

1.3 – 3.7 volts

Go to Step 15

Go to Step 18

15

1.

Turn OFF the ignition.

2.

Disconnect the ECM harness connectors.

3.

Disconnect the EHCU harness connectors.

4.

Disconnect the DRM harness connector.

5.

Turn ON the ignition, with the engine OFF.

6.

Connect a DMM between the CAN Low circuit
(pin 1 of B-387 connector) and a known good
ground at the resistor 1 harness connector.
Record the voltage reading.

7.

Connect a DMM between the CAN High circuit
(pin 2 of B-387 connector) and a known good
ground at the resistor 1 harness connector.
Record the voltage reading.

Are both voltage readings within the specified
value?

1.3 – 3.7 volts

Go to Step 16

Go to Step 23

16

1.

Turn OFF the ignition.

2.

Reconnect the DRM harness connector.

3.

Turn ON the ignition, with the engine OFF.

4.

Connect a DMM between the CAN Low circuit
(pin 1 of B-431 connector) and a known good
ground at the resistor 2 harness connector.
Record the voltage reading.

5.

Connect a DMM between the CAN High circuit
(pin 2 of B-431 connector) and a known good
ground at the resistor 2 harness connector.
Record the voltage reading.

Are both voltage readings within the specified
value?

1.3 – 3.7 volts

Go to Step 17

Go to Step 22

17

1.

Turn OFF the ignition.

2.

Reconnect the ECM harness connectors.

3.

Disconnect the DRM harness connectors.

4.

Turn ON the ignition, with the engine OFF.

5.

Connect a DMM between the CAN Low circuit
(pin 1 of B-431 connector) and a known good
ground at the resistor 2 harness connector.
Record the voltage reading.

6.

Connect a DMM between the CAN High circuit
(pin 2 of B-431 connector) and a known good
ground at the resistor 2 harness connector.
Record the voltage reading.

Are both voltage readings within the specified
value?

1.3 – 3.7 volts

Go to Diagnostic 

Aids

Go to Step 24

Step

Action

Value(s)

Yes

No

 Engine Control System (4HK1)    6E-289

18

1.

Turn OFF the ignition.

2.

Disconnect the ECM harness connectors.

3.

Disconnect the TCM harness connectors.

4.

Disconnect the EHCU harness connector.

5.

Disconnect the DRM harness connector.

6.

Turn ON the ignition, with the engine OFF.

7.

Test the CAN Low and CAN High circuits
among the resistor 1, resistor 2, ECM, EHCU
and DRM for a short to ground and short to
voltage.

Did you find and correct the condition?

—

Go to Step 38

Go to Step 19

19

1.

Turn OFF the ignition.

2.

Keep the ECM, TCM and DRM harness
connectors with disconnect.

3.

Reconnect the EHCU harness connector.

4.

Turn ON the ignition, with the engine OFF.

5.

Connect a DMM between the CAN Low circuit
(pin 1 of B-387 connector) and a known good
ground at the resistor 1 harness connector.
Record the voltage reading.

6.

Connect a DMM between the CAN High circuit
(pin 2 of B-387 connector) and a known good
ground at the resistor 1 harness connector.
Record the voltage reading.

Are both voltage readings within the specified
value?

1.3 – 3.7 volts

Go to Step 20

Go to Step 36

20

1.

Turn OFF the ignition.

2.

Reconnect the TCM harness connector.

3.

Turn ON the ignition, with the engine OFF.

4.

Connect a DMM between the CAN Low circuit
(pin 1 of B-387 connector) and a known good
ground at the resistor 1 harness connector.
Record the voltage reading.

5.

Connect a DMM between the CAN High circuit
(pin 2 of B-387 connector) and a known good
ground at the resistor 1 harness connector.
Record the voltage reading.

Are both voltage readings within the specified
value?

1.3 – 3.7 volts

Go to Step 21

Go to Step 35

21

1.

Turn OFF the ignition.

2.

Reconnect the ECM harness connectors.

3.

Turn ON the ignition, with the engine OFF.

4.

Connect a DMM between the CAN Low circuit
(pin 1 of B-387 connector) and a known good
ground at the resistor 1 harness connector.
Record the voltage reading.

5.

Connect a DMM between the CAN High circuit
(pin 2 of B-387 connector) and a known good
ground at the resistor 1 harness connector.
Record the voltage reading.

Are both voltage readings within the specified
value?

1.3 – 3.7 volts

Go to Step 34

Go to Step 37

Step

Action

Value(s)

Yes

No