Isuzu N-Series. Manual - part 790

 Engine Control System (4JH1)    6E-211

5

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 6

Go to Step 11

6

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 7

Go to Step 13

7

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 8

Go to Step 15

8

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 12

Go to Step 15

9

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 17

Go to Step 14

10

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 17

Go to Step 16

11

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 17

Go to Step 16

Step

Action

Value(s)

Yes

No

6E-212    Engine Control System (4JH1) 

12

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 15

Go to Diagnostic 

Aids

13

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 17

Go to Step 15

14

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 17

Go to Step 16

15

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 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

—

17

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.

5.

Monitor the DTC Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Step 18

18

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-213

P1690 (Symptom Code 4) (Flash Code 77)

Circuit Description
The malfunction indicator lamp (MIL) is located on the
instrument panel cluster (IPC).  The battery voltage is
supplied to the MIL.  The engine control module (ECM)
turns the MIL ON by grounding the MIL control circuit.
After a fixed time passes, the ECM turns OFF the MIL
with the ignition ON and the engine OFF.  The MIL has
the following functions:

• The MIL informs the driver that a malfunction has

occurred and the vehicle should be taken in for
service as soon as possible.

• The MIL illuminates during a bulb test and a

system test.

• A DTC will be stored if a MIL is requested by the

ECM.

If the ECM detects an open circuit or short circuit on the
MIL control circuit, this DTC will set.

Condition for Running the DTC

• The ignition switch is ON.  

Condition for Setting the DTC

• The ECM detects a low voltage condition on the

MIL control circuit for longer than 3 seconds when
the MIL is commanded OFF.

Action Taken When the DTC Sets

• The ECM does not illuminates the MIL when the

diagnostic runs and fails.

Condition for Clearing the DTC

• 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 P1690 (Symptom Code 4) (Flash Code 77)
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.

Perform the Malfunction Indicator Lamp (MIL)
test with the Tech 2.

4.

Command the MIL ON with the Tech 2.

Does the MIL turn ON when commanded ON with
the Tech 2?

—

Go to Step 3

Go to Step 4

3

Command the MIL OFF with the Tech 2.

Does the MIL OFF?

—

Go to Step 17

Go to Step 10

4

1.

Turn OFF the ignition.

2.

Inspect the Meter (10A) fuse (F-16) in the
glove box fuse block.

Is the Meter (10A) fuse (F-16) open?

—

Go to Step 5

Go to Step 6

5

Replace the Meter (10A) fuse (F-16).  If the fuse
continues to open, repair the short to ground on
one of the circuits that fed by the Meter (10A) fuse
(F-16) or replace the shorted attached component
fed by the Meter (10A) fuse (F-16).

Did you complete the repair?

—

Go to Step 19

—

6E-214    Engine Control System (4JH1) 

6

1.

Turn OFF the ignition.

2.

Disconnect the engine control module (ECM)
harness connector.

3.

Turn ON the ignition, with the engine OFF.

4.

Connect a 3-amp fused jumper wire between
the MIL control circuit of the ECM harness
connector (pin 42 of B-234 connector) and a
known good ground.

Does the MIL illuminate?

—

Go to Step 11

Go to Step 7

7

1.

Turn OFF the ignition.

2.

Remove the instrument panel cluster (IPC).

3.

Remove the MIL bulb from the IPC (meter
assembly).

Is the MIL bulb burned out?

—

Go to Step 15

Go to Step 8

8

1.

Disconnect the IPC harness B-51 connector.

2.

Connect a test lamp between the voltage feed
circuit of the MIL (pin 8 of B-51 connector) and
a known good ground.

3.

Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

—

Go to Step 9

Go to Step 12

9

1.

Turn OFF the ignition.

2.

Reconnect the ECM harness connector.

3.

Connect a test lamp between the voltage feed
circuit and control circuit of the MIL (pins 4 and
8 of B-51 connector).

4.

Turn ON the ignition, with the engine OFF.

5.

Perform the MIL test with the Tech 2.

6.

Command the MIL ON with the Tech 2.

Does the test lamp turn ON when commanded ON
with the Tech 2?

—

Go to Step 14

Go to Step 13

10

1.

Test the control circuit of the MIL between the
ECM (pin 42 of B-234 connector) and the IPC
(pin 4 of B-51 connector) for a short to ground.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 18

11

1.

Turn OFF the ignition.

2.

Disconnect the ECM harness connector.

3.

Inspect for an intermittent and for a poor
connection on the MIL control circuit at the
harness connector of the ECM (pin 42 of B-
234 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 19

Go to Step 18

12

Repair the open circuit or high resistance on the
voltage feed circuit of the MIL between the IPC (pin
8 of B-51 connector) and Meter (10A) fuse (F-16).

Did you complete the repair?

—

Go to Step 19

—

Step

Action

Value(s)

Yes

No