Isuzu N-Series. Manual - part 789

 Engine Control System (4JH1)    6E-207

6

1.

Keep the ignition switch ON, with the engine
OFF.

2.

Connect a DMM between the CAN High signal
circuit (pin 2 of E-110 connector) and a known
good ground.

Is the DMM voltage within the specified value?

3.0 – 4.0 volts

Go to Step 7

Go to Step 12

7

1.

Turn OFF the ignition.

2.

Reconnect the PCU harness connector.

3.

Disconnect the engine control module (ECM)
B-233 harness connector.  Keep the ECM B-
234 harness connector with connected.

4.

Connect a DMM across the CAN harness
(pins 99 and 100 of B-233 connector).

5.

Measure the resistance across the CAN
terminals.

Is the resistance within the specified value?

110 – 130 

Ω

Go to Step 8

Go to Step 14

8

1.

Connect a DMM between the CAN Low signal
circuit of the ECM harness (pin 99 of B-233
connector) and a known good ground.

2.

Turn ON the ignition, with the engine OFF.

Is the DMM voltage within the specified value?

1.5 – 2.5 volts

Go to Step 9

Go to Step 16

9

1.

Keep the ignition switch ON, with the engine
OFF.

2.

Connect a DMM between the CAN High signal
circuit of the ECM harness (pin 100 of B-233
connector) and a known good ground.

Is the DMM voltage within the specified value?

3.0 – 4.0 volts

Go to Step 13

Go to Step 16

10

1.

Test the CAN Low and High circuit between
the ECM (pins 99 and 100 of B-233
connector) and the PCU (pins 1 and 2 of E-
110 connector) for the following conditions: 

• An open circuit
• A short each other
• High resistance.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 18

Go to Step 15

11

1.

Test the CAN Low circuit between the ECM
(pin 99 of B-233 connector) and the PCU (pin
1 of E-110 connector) for the following
conditions:

• A short to ground
• A short to battery or ignition voltage

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 18

Go to Step 17

12

1.

Test the CAN Low circuit between the ECM
(pin 100 of B-233 connector) and the PCU (pin
2 of E-110 connector) for the following
conditions:

• A short to ground
• A short to battery or ignition voltage

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 18

Go to Step 17

Step

Action

Value(s)

Yes

No

6E-208    Engine Control System (4JH1) 

13

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.

Turn ON the ignition, with the engine OFF.

5.

Monitor the DTC Information with the Tech 2.

Is DTC P0251 (Symptom Code E) set?

—

Go to Step 16

Go to Diagnostic 

Aids

14

1.

Turn OFF the ignition.

2.

Disconnect the PCU harness connector.

3.

Inspect for an intermittent and for poor
connections at the harness connector of the
PCU (pins 1 and 2 of E-110 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 18

Go to Step 16

15

1.

Turn OFF the ignition.

2.

Disconnect the ECM harness connector.

3.

Inspect for an intermittent and for poor
connections on the CAN Low or High circuits
at the harness connector of the ECM (pins 99
and 100 of B-233 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 18

Go to Step 17

16

Important:
The fuel injection pump must be timed to the
engine.

Replace the fuel injection pump.  Refer to Fuel
Injection Pump Replacement in engine mechanical
section.  (PCU is part of the fuel injection pump
assembly)

Did you complete the replacement?

—

Go to Step 18

—

17

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 18

—

18

1.

Reconnect all previously disconnected
harness connector(s).

2.

Clear the DTCs with the Tech 2.

3.

Start the engine.

4.

Monitor the DTC Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 2

Go to Step 19

19

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

 Engine Control System (4JH1)    6E-209

P1650 (Symptom Code B) (Flash Code 44)

Circuit Description
The engine control module (ECM) calculates the
desired fuel injection quantity and timing using data
sent from various sensors.  These desired data are
sent to the fuel injection pump control unit (PCU) via a
controller area network (CAN) communication bus.
The PCU also receives signals from the internal inputs:
pump camshaft position (CMP) sensor that is located
inside the fuel injection pump to determine the cam ring
rotation angle and the fuel injection pump speed.  The
fuel temperature (FT) sensor is internal the PCU.
These values are used to compare the desired values
sent from the ECM then PCU determines the injection
timer piston position and fuel injection quantity, and
actuates timing control valve (TCV) & fuel injection
solenoid valve based on control maps in the PCU.
The ECM monitors CAN operational status by
expecting a constant flow of messages from the PCU.
If the ECM detects internal CAN controller does not
react, this DTC will set.

Condition for Setting the DTC

• The ECM detects internal CAN controller does not

react.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM cuts the fuel injection.

Condition for Clearing the MIL/DTC

• The ECM turns OFF the MIL when the diagnostic

runs and does not fail.

• A history DTC clears after 40 consecutive driving

cycles without a fault.  Or clear with the Tech 2.

Notice:

• CAN controller is internal to the ECM.

DTC P1650 (Symptom Code B) (Flash Code 44)

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.

Turn ON the ignition, with the engine OFF.

4.

Monitor the Diagnostic Trouble Code (DTC)
Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Step 4

3

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 4

—

4

1.

Clear the DTCs with the Tech 2.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

Monitor the DTC Information with the Tech 2.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 5

5

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

6E-210    Engine Control System (4JH1) 

P1651 (Symptom Code A, B) (Flash Code 45)

Circuit Description
The engine control module (ECM) calculates the
desired fuel injection quantity and timing using data
sent from various sensors.  These desired data are
sent to the fuel injection pump control unit (PCU) via a
controller area network (CAN) communication bus.
The PCU also receives signals from the internal inputs:
pump camshaft position (CMP) sensor that is located
inside the fuel injection pump to determine the cam ring
rotation angle and the fuel injection pump speed.  The
fuel temperature (FT) sensor is internal the PCU.
These values are used to compare the desired values
sent from the ECM then PCU determines the injection
timer piston position and fuel injection quantity, and
actuates timing control valve (TCV) & fuel injection
solenoid valve based on control maps in the PCU.
The ECM monitors CAN operational status by
expecting a constant flow of messages from the PCU.
If the ECM fails to receive an expected message from
the PCU, this will set depending on what
communication is lost.

Condition for Setting the DTC

• The ECM detects that the PCU does not receive

the CAN messages from the ECM.  (Symptom
Code A)

• The ECM does not receive the CAN messages

from the PCU.  (Symptom Code B)

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM cuts the fuel injection.

Condition for Clearing the MIL/DTC

• The ECM turns OFF the MIL when the diagnostic

runs and does not fail.

• A history DTC clears after 40 consecutive driving

cycles without a fault.  Or clear with the Tech 2.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

DTC P1651 (Symptom Code A, B) (Flash Code 45)
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 OFF the ignition for 30 seconds.

3.

Start the engine.

4.

Monitor the Diagnostic Trouble Code (DTC)
Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Step 4

3

1.

Turn OFF the ignition.

2.

Disconnect the fuel injection pump control unit
(PCU) harness connector.

3.

Connect a DMM across the controller area
network (CAN) harness (pins 1 and 2 of E-110
connector).

4.

Measure the resistance across the CAN
terminals.

Is the resistance within the specified value?

110 – 130 

Ω

Go to Step 4

Go to Step 9

4

1.

Connect a DMM between the CAN Low signal
circuit (pin 1 of E-110 connector) and a known
good ground.

2.

Turn ON the ignition, with the engine OFF.

Is the DMM voltage within the specified value?

1.5 – 2.5 volts

Go to Step 5

Go to Step 10