Isuzu KB P190. Manual - part 859

Engine Management – V6 – Diagnostics 

Page 6C1-2–158 

 

Step Action 

Yes 

No 

5 

1 

Connect a test lamp between the control circuit of the A/C relay 
and a 12 V. 

2 

Switch on the ignition with the engine not running. 

3 

Using Tech 2, command the A/C relay on and then off. 

Does the test lamp turn on and off when the A/C relay is commanded 
on and off? 

Go to Step 8 

Go to Step 7 

6 

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

Was the repair completed? 

Go to Step 10 

— 

7 

Test the control circuit of the A/C relay 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 10 

Go to Step 9 

8 

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

Was the repair completed? 

Go to Step 10 

— 

9 

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

Was the repair completed? 

Go to Step 10 

— 

10  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 A/C relay control circuit DTCs fail this ignition cycle?

Go to Step 2 

Go to Step 11 

11  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. 

7.39  DTC P0685, P0686 or P0687 

DTC Descriptors 

This diagnostic procedure supports the following DTCs: 

• 

DTC P0685 – Engine Control Ignition Relay Circuit Malfunction 

• 

DTC P0686 – Engine Control Ignition Relay Circuit Low Voltage 

• 

DTC P0687 – Engine Control Ignition Relay Circuit High Voltage 

Circuit Description 

The supply voltage circuit of the engine control relay is directly connected to battery voltage. When the ignition switch is 
turned on, the ECM grounds the relay control circuit to provide ignition voltage to various sensors and components that 
controls the engine operation. 

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

Engine Management – V6 – Diagnostics 

Page 6C1-2–159 

 

Conditions for Running the DTC 

DTCs P0685, P0686 and P0687 run continuously once the following conditions are met: 

• 

The ignition is switched on 

• 

The ignition voltage is 10.0 – 16.0 V. 

Conditions for Setting the DTC 

The ECM detects a condition that is incorrect for the engine control relay commanded state. 

Conditions for Clearing the DTC 

The engine control 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. 

• 

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. 

Test Description 

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

4 

Removal of the ECM Fuse 29 enables the ECM to power down completely prior to the test procedure. 

DTC P0685, P0686 or P0687 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 P0685, P0686 and P0687 fail this ignition cycle? 

Go to Step 3 

Refer to Additional 

Information in this 

DTC 

3 

1 

Remove the engine control relay. Refer to 8A Electrical - Body 
and Chassis. 

2 

Connect a test lamp between the battery voltage circuit of the 
engine control relay and a good ground. 

Does the test lamp illuminate? 

Go to Step 4 

Go to Step 5 

4 

1 

Switch off the ignition. 

2 

Remove and reinstall the ECM fuse 29 from the engine 
compartment fuse and relay panel assembly. 

3 

Connect a test lamp between the control circuit and the battery 
voltage circuit of the engine control relay. 

4 

Switch on the ignition. 

Does the test lamp switches from off to on when the ignition switch is 
turned form off to on? 

Go to Step 7 

Go to Step 6 

Engine Management – V6 – Diagnostics 

Page 6C1-2–160 

 

Step Action 

Yes 

No 

5 

Repair the high resistance or open circuit fault condition in the battery 
voltage circuit of the engine control 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 engine control 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 engine control 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 engine control 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. 

7.40 DTC 

P0700 

DTC Descriptor 

This diagnostic procedure supports DTC P0700 – Malfunction Indicator (MI) Request from Transmission Control Module 
(TCM). 

Circuit Description 

The engine control module (ECM) communicates directly with the transmission control module (TCM) and other control 
modules connected to the GM LAN serial data communication circuit through the GM LAN protocol. 

DTC P0700 – Malfunction Indicator Request from TCM sets if the following condition exists: 

• 

The TCM detects an emission related fault condition and sets a TCM DTC that represent the fault condition. 

• 

The ECM receives a serial data signal from the TCM requesting the illumination of the malfunction indicator. 

Conditions for Running the DTC 

DTC P0700 runs continuously when the ignition is switched on. 

Conditions for Setting the DTC 

The ECM receives a serial data signal from the TCM requesting the illumination of the malfunction indicator lamp (MIL). 

Engine Management – V6 – Diagnostics 

Page 6C1-2–161 

 

Conditions for Clearing the DTC 

DTC P0700 – Malfunction Indicator Request from TCM is a Type A DTCs. Refer to 1.4 

Diagnostic Trouble Codes in 

this Section, for action taken when a Type A DTC sets and conditions for clearing Type A DTCs. 

Additional Information 

• 

Refer to 6C1-1 Engine Management – V6 – General Information for details of the ECM operation. 

• 

For an intermittent fault condition, refer to 5.2 

Intermittent Fault Conditions in this Section. 

• 

To assist diagnosis, refer to 3 

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

diagram and connector charts. 

DTC P0700 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 P0700 fail this ignition cycle? 

Go to Step 3 

Refer to Additional 

Information in this 

DTC 

3 

Are other powertrain DTCs also set? 

Go to the 

appropriate DTC 

Table in this Section 

Refer to 7C2 

Automatic 

Transmission – 

4L60E – Electrical 

Diagnosis 

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

7.41 DTC 

P0704 

DTC Descriptor 

This diagnostic procedure supports DTC P0704 – Clutch Switch Input Circuit Malfunction. 

Circuit Description 

The clutch pedal switch disengages the cruise control when the clutch is depressed, in much the same way that the 
brake pedal switch is used to disengage the cruise control feature. 

The cruise control cancel switch is normally closed when the clutch pedal is at rest, opening when the pedal is pressed. 
Activation of this switch removes the signal to the ECM which will then deactivate the cruise control. 

Conditions for Running the DTC 

Runs continuously when the ignition is switched and the engine is running. 

Conditions for Setting the DTC 

The ECM detects 15 gear changes with less than three clutch switch inputs. 

N O T E  

The ECM determines that a gear change has 
been performed by the engine speed / vehicle 
speed ratio.