Isuzu N-Series. Manual - part 708

6E-254    Engine Control System (4HK1) 

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

Step

Action

Value(s)

Yes

No

 Engine Control System (4HK1)    6E-255

P1625 (Flash Code 416)

Circuit Description
The engine control module (ECM) main relay is
energized to feed the battery voltage to the ECM
through the relay switch side when the ECM receives
an ignition voltage switch ON signal. When the ignition
switch is OFF, the ECM main relay is de-energized
after a certain length of time passed.
If the ECM detects the ECM main relay is turned OFF
before ECM commanded OFF, this DTC will set. (ECM
main relay open stuck DTC)
If the ECM detects the ECM has been ON when the
relay is commanded OFF, this DTC will also set. (ECM
main relay close stuck DTC)

Condition for Running the DTC
ECM main relay open stuck DTC

• DTC P1630 is not set.
• The ignition switch is ON.
• The ignition voltage is more than 18 volts.
• The ignition ON time is longer than 3 seconds.

Condition for Setting the DTC
ECM main relay open stuck DTC

• The ECM detects a low voltage condition on the

ECM main relay voltage feed circuit when the relay
is commanded ON for longer than 5 seconds.

ECM main relay close stuck DTC

• The ECM detects that the ECM has been ON

when the relay is commanded OFF for longer than
10 seconds.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

Condition for Clearing the MIL / DTC

• The ECM turns OFF the MIL when the key is

cycled after a current DTC clears.

• A current DTC clears when the diagnostic runs and

does not fail.

• A history DTC clears after 20 consecutive driving

cycles without a fault. Or clear with the Tech 2 or
accelerator pedal operation.

Diagnostic Aid

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

• Faulty or sticking ECM main relay will set this DTC.

DTC P1625 (Flash Code 416)
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.

Turn ON the ignition.

4.

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

Does the DTC fail this ignition?

—

Go to Step 3

Go to Diagnostic 

Aids

3

Does the engine start?

—

Go to Step 4

Go to Step 8

4

1.

Turn OFF the ignition.

2.

Disconnect the ECM main relay.

Does the engine start?

—

Go to Step 5

Go to Step 6

5

Repair the short to battery on the voltage feed
circuits to the engine control module (ECM)
between the ECM (pins 2 and 5 of J-191
connector) and the ECM main relay (pin 2 of X-18
connector).

Did you complete the repair?

—

Go to Step 13

—

6E-256    Engine Control System (4HK1) 

6

1.

Turn OFF the ignition for 30 seconds.

2.

Replace the ECM main relay with the glow
relay or replace with a known good relay.

3.

Turn ON the ignition, with the engine OFF.

4.

Turn ON the ignition.

5.

Monitor the DTC Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 7

Go to Step 11

7

1.

Test the voltage supply circuits to the ECM
main relay between the ECM (pins 21 and 40
of J-191 connector) and the ECM main relay
(pin 4 of X-18 connector) for a short to battery.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

8

1.

Turn OFF the ignition for 30 seconds.

2.

Replace the ECM main relay with the glow
relay or replace with a known good relay.

3.

Start the engine.

Does the engine start?

—

Go to Step 11

Go to Step 9

9

1.

Turn OFF the ignition.

2.

Inspect for an intermittent, for poor tightening
and corrosion at the chassis ground terminal
(J-9).

3.

Repair the tightening or clean the corrosion as
necessary.

4.

Inspect the ECM (40A) slow blow fuse for
open.

5.

Replace the ECM (40A) slow blow fuse if
open. If it continues to open, repair the short to
ground on one of the circuits that is fed by the
ECM (40A) slow blow fuse.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 10

Step

Action

Value(s)

Yes

No

 Engine Control System (4HK1)    6E-257

10

1.

Turn OFF the ignition.

2.

Disconnect the ECM main relay.

3.

Inspect for an intermittent and for poor
connections and corrosion on each ECM main
relay terminal (pins 2, 3, 4 and 5 of X-18
connector).

4.

Disconnect the ECM harness connector.

5.

Inspect for an intermittent, for poor
connections and corrosion on the ECM main
relay voltage supply and feed circuits at the
harness connector of the ECM (pins 2, 5, 21
and 40 of J-191 connector).

6.

Test for high resistance on each ECM main
relay circuit.

• Between pins 2 and 5 of J-191 and pin 2

of X-18 connector

• Between pins 21 and 40 of J-191

connector and pin 4 of X-18 connector

• Between ECM (40A) slow blow fuse and

pin 3 of X-18 connector

• Between pin 5 of X-18 connector and

chassis ground (J-9)

7.

Repair the connection(s) or circuit(s) as
necessary.

Did you find and correct the condition?

—

Go to Step 13

Go to Step 12

11

Replace the ECM main relay.

Did you complete the replacement?

—

Go to Step 13

—

12

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 13

—

13

1.

Reconnect all previously disconnected relay
or harness connector(s).

2.

Clear the DTCs with the Tech 2.

3.

Turn OFF the ignition for 30 seconds.

4.

Turn ON the ignition.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 14

14

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