Isuzu N-Series. Manual - part 440

6E-96 EMISSION AND ELECTRICAL DIAGNOSIS

DTC-P42 Quick On Start (QOS) Relay Control Circuit High Voltage

N6A1212E

EMISSION AND ELECTRICAL DIAGNOSIS 6E-97

Location of Relay

Legend

1. Relay box (Installed on the left side rear of the 

cab)

N6A1184E

NO

RELAY NAME

X-20

Glow plug

X-21

Starter

X-22

Marker lamp

X-23

Rear fog

X-24

A/C COMP, 4WD ind. lamp

X-25

Exh, Brake control

X-26

CSD, A/C ON SIGNAL

X-27

Condenser fan

X-28

Exh. Brake cut

6E-98 EMISSION AND ELECTRICAL DIAGNOSIS

Inspection for quick on start (QOS) power cut relay

Resistance value

Legend

A. QOS relay

N6A1214E

Legend

A. QOS relay

N6A1215E

Inspection Point

Resistance

Reference

Inspection 
relay unit

4 

←→  5

23  (

Ω) (for 12 volt)

100 (

Ω) (for 24 volt)

2 

←→ 3

∞

Not be supplied electricity to coil

Below 0.5 (

Ω)

Be supplied electricity to coil

EMISSION AND ELECTRICAL DIAGNOSIS 6E-99

Step

Action

Value

YES

NO

1

Was the “on-board diagnostic (OBD) system
check” performed?

—

Go to Step 2

Go to self diag 

system check

2

1. Ignition “OFF”, with scan tool disconnect-

ed.

2. Disconnect the Relay solenoid switch

from the Relay box.

3. Apply a circuit tester with the voltage

range or a test light to the output circuit for
the Relay.

4. Ignition “ON”, Engine “OFF”.

Is voltage as prescribed, or is test Light lit until
18 seconds?

≥8V or light 

“ON” (for 12 

Volt)

≥16V or light 

“ON” (for 24 

Volt)

Go to Step 3

Go to Step 4

3

1. Ignition “OFF”
2. Disconnect the ECM connector from

ECM.

3. Check the short to voltage of Relay circuit

between the ECM and Relay connector.

4. Repair if necessary.

Has DTC 42 been corrected?

—

Go to Step 6

Go to Step 5

4

Replace the VSV.

Is the action complete?

—

Go to Step 6

—

5

Replace the ECM.

Is the action complete?

—

Go to Step 6

—

6

1. Reconnect all the connectors removed.
2. Ignition “ON”, Engine “OFF”

Is DTC 42 all right under Scan Tool Check?

—

Go to Step 7

Go to Step 2

7

Is any current trouble other than DTC 42 dis-
played by scan tool?

—

Go to trouble code 

section

Trouble code clear