Isuzu KB P190. Manual — part 858

Engine Management – V6 – Diagnostics

Page 6C1-2–154

•

Refer to 6D1-1 Charging System – V6 for details of the charging system operation.

•

Since fault condition in a wiring connector may trigger DTCs, always test the connectors related to this diagnostic
procedure for shorted terminals or poor wiring connection before replacing any component. Refer to 8A Electrical -
Body and Chassis for information on electrical fault diagnosis.

•

To assist diagnosis, refer to 3

Wiring Diagrams and Connector Charts in this Section, for the system wiring

diagram and connector charts.

DTC P0625 or P0626 Diagnostic Table

Step Action

Yes

No

1

Has the Diagnostic System Check been performed?

Go to Step 2

Refer to

4.4 Diagnostic
System Check in

this Section

2

1

Switch off the ignition for 30 seconds.

2

Operate the vehicle within the conditions for running the DTC.

3

Using Tech 2, select the DTC display function.

Does DTC P0625 or P0626 fail this ignition cycle?

Go to Step 3

Refer to Additional

Information in this

DTC

3

Test the charging system for any fault condition that may cause
incorrect generator operation. Refer to 6D1-1 Charging System – V6.

Was any fault found and rectified?

Go to Step 6

Go to Step 4

4

Test the Gen F signal circuit for a high resistance, open circuit, short
to ground or short to voltage fault condition. Refer to 8A Electrical -
Body and Chassis for information on electrical fault diagnosis.

Was any fault found and rectified?

Go to Step 6

Go to Step 5

5

Replace the ECM. Refer to Refer to 6C1-3 Engine Management – V6
– Service Operations.

Was the repair completed?

Go to Step 7

—

6

1

Using Tech 2, clear the DTCs.

2

Switch off the ignition for 30 seconds.

3

Start the engine.

4

Operate the vehicle within the conditions for running the DTC.

Does any of the Generator F-terminal circuit DTCs fail this ignition
cycle?

Go to Step 2

Go to Step 8

7

Using Tech 2, select the DTC display function.

Does Tech 2 display any DTCs?

Go to the

appropriate DTC

Table in this Section

System OK

When all diagnosis and repairs are completed, check the system for correct operation.

7.37 DTC P0627, P0628 or P0629

DTC Descriptors

This diagnostic procedure supports the following DTCs:

•

DTC P0627 – Fuel Pump Relay Circuit Malfunction

•

DTC P0628 – Fuel Pump Relay Voltage Low

•

DTC P0629 – Fuel Pump Relay Voltage High

Engine Management – V6 – Diagnostics

Page 6C1-2–155

Circuit Description

The ground circuit of the fuel pump relay coil is directly connected to ground. When the ignition switch is turned on and
all the conditions required to enable fuel pump operation are met, the ECM applies battery voltage to the fuel pump relay
control circuit to operate the fuel pump. Refer to 6C Fuel System – V6 for further information.

The ECM monitors the control circuit of the fuel pump relay for conditions that are incorrect for the commanded state. A
fuel pump relay control circuit DTC sets if the ECM detects a fault condition in this circuit.

Conditions for Running the DTC

Run continuously once the following conditions are met:

•

the ignition is switched on, and

•

the ignition voltage is 10.0 – 16.0 V.

Conditions for Setting the DTC

The ECM detects a condition that are incorrect for the fuel pump relay commanded state.

Conditions for Clearing the DTC

The fuel pump relay control circuit DTCs are Type C DTCs. Refer to 1.4

Diagnostic Trouble Codes in this Section, for

action taken when Type C DTCs set and conditions for clearing Type C DTCs.

Additional Information

•

Refer to 6C Fuel System – V6 for details of the fuel pump operation.

•

For an intermittent fault condition, refer to 5.2

Intermittent Fault Conditions in this Section.

•

Since fault condition in a wiring connector may trigger DTCs, always test the connectors related to this diagnostic
procedure for shorted terminals or poor wiring connection before replacing any component. Refer to 8A Electrical -
Body and Chassis for information on electrical fault diagnosis.

•

To assist diagnosis, refer to 3

Wiring Diagrams and Connector Charts in this Section, for the system wiring

diagram and connector charts.

DTC P0627 to P0629 Diagnostic Table

Step Action

Yes

No

1

Has the Diagnostic System Check been performed?

Go to Step 2

Refer to

4.4 Diagnostic

System Check in

this Section

2

1

Switch off the ignition for 30 seconds.

2

Turn the ignition switch to the Start position or operate the
vehicle within the conditions for running the DTC.

3

Using Tech 2, select the DTC display function.

Does DTC P0627, P0628 and P0629 fail this ignition cycle?

Go to Step 3

Refer to Additional

Information in this

DTC

3

1

Remove the fuel pump relay. Refer to 8A Electrical - Body and
Chassis.

2

Connect a test lamp between the ground circuit of the fuel pump
relay and a 12 V.

Does the test lamp illuminate?

Go to Step 4

Go to Step 5

4

1

Connect a test lamp between the control circuit and ground
circuit of the fuel pump relay.

2

Using Tech 2, command the fuel pump relay on.

Does the test lamp switch from off to on as Tech 2 commands the fuel
pump relay from off to on?

Go to Step 7

Go to Step 6

Engine Management – V6 – Diagnostics

Page 6C1-2–156

Step Action

Yes

No

5

Repair the high resistance or open circuit fault condition in the ground
circuit of the fuel pump relay. Refer to 8A Electrical - Body and
Chassis for information on electrical wiring repair procedures.

Was the repair completed?

Go to Step 9

—

6

Test the control circuit of the fuel pump relay for a high resistance,
open circuit, short to ground or a short to voltage fault condition. Refer
to 8A Electrical - Body and Chassis for information on electrical fault
diagnosis.

Was any fault found and rectified?

Go to Step 9

Go to Step 8

7

Replace the fuel pump relay. Refer to 8A Electrical - Body and
Chassis.

Was the repair completed?

Go to Step 9

—

8

Replace the ECM. Refer to 6C1-3 Engine Management – V6 –
Service Operations.

Was the repair completed?

Go to Step 9

—

9

1

Using Tech 2, clear the DTCs.

2

Switch off the ignition for 30 seconds.

3

Start the engine.

4

Operate the vehicle within the conditions for running the DTC.

Does the fuel pump relay control circuit DTCs fail this ignition cycle?

Go to Step 2

Go to Step 10

10 Using Tech 2, select the DTC display function.

Does Tech 2 display any DTCs?

Go to the

appropriate DTC

Table in this Section

System OK

When all diagnosis and repairs are completed, check the system for correct operation.

7.38 DTC P0645, P0646 or P0647

DTC Descriptors

This diagnostic procedure supports the following DTCs:

•

DTC P0645 – A/C Relay Circuit Malfunction.

•

DTC P0646 – A/C Relay Voltage Low.

•

DTC P0647 – A/C Relay Voltage High.

Circuit Description

The engine control relay applies battery voltage to the coil circuit of the air-conditioning (A/C) clutch relay through the
ignition circuit. Using a device called a driver, the ECM grounds control circuit of the A/C relay to activate the A/C clutch
and operate the A/C compressor. Refer to 2A Heater and Air-conditioning for details of the A/C compressor operation.

The driver has a feedback circuit that is pulled-up to a voltage. The ECM monitors the driver feedback circuit to
determine if the control circuit is open, shorted to ground or shorted to a positive voltage.

An A/C relay control circuit DTC sets if the ECM detects a fault condition in the A/C relay control circuit.

Conditions for Running the DTC

DTC P0645, P0646 or P0647 runs continuously once the following conditions are met:

•

The ignition voltage is 10 – 16 V.

•

The engine speed is greater than 80 rpm

Engine Management – V6 – Diagnostics

Page 6C1-2–157

Conditions for Setting the DTC

Conditions for Setting DTC P0645

The ECM detects an open circuit fault condition in the A/C relay control circuit.

Conditions for Setting DTC P0646

The ECM detects a short to ground fault condition in the A/C relay control circuit.

Conditions for Setting DTC P0647

The ECM detects a short to voltage fault condition in the A/C relay control circuit.

Conditions for Clearing the DTC

The A/C relay control circuit DTCs are Type C DTCs. Refer to 1.4

Diagnostic Trouble Codes in this Section, for

action taken when Type C DTCs set and conditions for clearing Type C DTCs.

Additional Information

•

For an intermittent fault condition, refer to 5.2

Intermittent Fault Conditions in this Section.

•

Refer to 2A Heater and Air-conditioning for details of the A/C system operation.

•

Since a fault condition in a wiring connector may trigger DTCs, always test the connectors related to this
diagnostic procedure for shorted terminals or poor wiring connection before replacing any component. Refer to 8A
Electrical - Body and Chassis for information on electrical fault diagnosis.

•

To assist diagnosis, refer to 3

Wiring Diagrams and Connector Charts in this Section, for the system wiring

diagram and connector charts.

Test Description

The following number refers to the step numbers in the diagnostic table:

3

A fault condition in the HVAC system may trigger this DTC.

DTC P0645, P0646 or P0647 Diagnostic Table

Step Action

Yes

No

1

Has the Diagnostic System Check been performed?

Go to Step 2

Refer to

4.4 Diagnostic
System Check in

this Section

2

1

Switch off the ignition for 30 seconds.

2

Switch on the A/C system or operate the vehicle within the
conditions for running the DTC.

3

Using Tech 2, select the DTC display function.

Does DTC P0645 P0646 or P0647 fail this ignition cycle?

Go to Step 3

Refer to Additional

Information in this

DTC

3

Check for a fault condition in the HVAC system, which can disable the
AC compressor clutch. Refer to 2A Heater and Air-conditioning for
details of the A/C compressor operation.

Was any fault found and rectified?

Go to Step 10

Go to Step 4

4

1

Remove the A/C relay. Refer to 8A Electrical - Body and
Chassis.

2

Connect a test lamp between the ignition circuit of the A/C relay
coil and the ECM housing.

3

Switch on the ignition with the engine not running.

Does the test lamp illuminate?

Go to Step 5

Go to Step 6