Isuzu N-Series. Manual - part 775

 Engine Control System (4JH1)    6E-151

4

1.

Test the control circuit of the A/C compressor
relay between the ECM (pin 41 of B-234
connector) and the A/C compressor relay (pin
2 of X-24 connector) for a short to battery or
ignition voltage.

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Step 6

5

Replace the A/C compressor relay.

Did you complete the replacement?

—

Go to Step 7

—

6

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 7

—

7

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.

Start the engine.

5.

Turn ON the blower motor switch and the A/C
compressor switch.

6.

Monitor the DTC Information with the Tech 2
when the A/C Relay Command parameter is
ON.

Did the DTC fail this ignition?

—

Go to Step 3

Go to Step 8

8

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

6E-152    Engine Control System (4JH1) 

P0703 (Symptom Code A, B) (Flash Code 25)

Circuit Description
The brake pedal switch is installed on the brake pedal
bracket.  The brake pedal 1 switch is a normally open
type switch and the brake pedal 2 switch is a normally
closed type switch.  When the brake pedal is pressed,
the brake pedal 1 switch signal is provided to the
engine control module (ECM) and the stoplights are
turned ON.  Then, the brake pedal 2 switch signal to
the ECM is stopped (low voltage).  If the ECM detects
the brake switch signals out of correlation, this DTC will
set.

Condition for Running the DTC

• The ignition switch is ON.
• The engine speed is higher than 1500 RPM.
• The accelerator pedal position is more than 10%.
• The vehicle speed is higher than 15 km/h (9 MPH).

Condition for Setting the DTC

• The ECM detects that the brake pedal 1 switch

(normally open type switch) signal and brake pedal
2 switch (normally closed type switch) signal
correlation error for longer than 30 seconds within
the enabling conditions ever since ignition switch is
ON.  (Symptom Code A)

• The ECM detects that the brake pedal 1 switch

(normally open type switch) signal and brake pedal
2 switch (normally closed type switch) signal
correlation error for longer than 30 seconds.
(Symptom Code B)

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 diagnostic

runs and does not fail.

• 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.

• Misadjusted brake pedal switch will cause this

DTC to set.

DTC P0703 (Symptom Code A, B) (Flash Code 25)
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.

Observe the Brake Pedal 1 Switch parameter
with the Tech 2 while fully depressing and
releasing the brake pedal.

Does the Tech 2 indicate Applied when the brake
pedal is applied and Released when the brake
pedal is released?

—

Go to Step 10

Go to Step 3

3

1.

Check to ensure the brake pedal switch is
adjusted correctly.  The plunger should be all
the way in when the pedal is released, yet
should not impede with the brake pedal full
upward travel.

2.

Adjust the brake pedal switch as necessary.

Did you find and correct the condition?

—

Go to Step 20

Go to Step 4

4

1.

Turn OFF the ignition.

2.

Inspect the Stop Light (10A) fuse (F-5) in the
glove box fuse block.

Is the Stop Light (10A) fuse (F-5) open?

—

Go to Step 5

Go to Step 6

 Engine Control System (4JH1)    6E-153

5

Replace the Stop Light (10A) fuse (F-5).  If the fuse
continues to open, repair the short to ground on
one of the circuits that is fed by the Stop Light (10A)
fuse (F-5) or replace the shorted attached
component fed by the Stop Light (10A) fuse (F-5).

Did you complete the repair?

—

Go to Step 20

—

6

1.

Turn OFF the ignition.

2.

Disconnect the brake pedal switch harness
connector.

3.

Connect a test lamp between the voltage feed
circuit of the brake pedal 1 switch harness (pin
1 of B-66 connector) and a known good
ground.

Does the test lamp illuminate?

—

Go to Step 7

Go to Step 8

7

1.

Turn ON the ignition, with the engine OFF.

2.

Observe the Brake Pedal 1 Switch parameter
with the Tech 2 while momentarily jumping 3-
amp fused jumper wire across the brake pedal
1 switch harness connector between pins 1
and 4 of the B-66 connector.

Does the Tech 2 indicate Applied when the circuit is
jumpered and Released when the circuit is not
jumpered?

—

Go to Step 16

Go to Step 9

8

Repair the open circuit or high resistance on the
voltage feed circuit between the Stop Light (10A)
fuse (F-5) and the brake pedal 1 switch (pin 1 of B-
66 connector).

Did you complete the repair?

—

Go to Step 20

—

9

1.

Test the brake pedal 1 switch signal circuit
between the ECM (pin 30 of B-234 connector)
and the brake pedal 1 switch (pin 4 of B-66
connector) for the following conditions:

• An open circuit
• A short to battery or ignition voltage
• High resistance

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 20

Go to Step 17

10

Observe the Brake Pedal 2 Switch parameter with
the Tech 2 while fully depressing and releasing the
brake pedal.

Does the Tech 2 indicate Applied when the brake
pedal is applied and Released when the brake
pedal is released?

—

Go to Diagnostic 

Aids

Go to Step 11

11

1.

Check to ensure the brake pedal switch is
adjusted correctly.  The plunger should be all
the way in when the pedal is released, yet
should not impede with the brake pedal full
upward travel.

2.

Adjust the brake pedal switch as necessary.

Did you find and correct the condition?

—

Go to Step 20

Go to Step 12

Step

Action

Value(s)

Yes

No

6E-154    Engine Control System (4JH1) 

12

1.

Turn OFF the ignition.

2.

Disconnect the brake pedal switch harness
connector.

3.

Turn ON the ignition, with the engine OFF.

4.

Connect a test lamp between the voltage feed
circuit of the brake pedal 2 switch harness (pin
2 of B-66 connector) and a known good
ground.

Does the test lamp illuminate?

—

Go to Step 13

Go to Step 14

13

1.

Turn ON the ignition, with the engine OFF.

2.

Observe the Brake Pedal 2 Switch parameter
with the Tech 2 while momentarily jumping 3-
amp fused jumper wire across the brake pedal
2 switch harness connector between pins 2
and 3 of the B-66 connector.

Does the Tech 2 indicate Released when the circuit
is jumpered and Applied when the circuit is not
jumpered?

—

Go to Step 16

Go to Step 15

14

Repair the open circuit or high resistance on the
voltage feed circuit between the ECM main relay
(pin 5 of X-14 connector) and the brake pedal 2
switch (pin 2 of B-66 connector).

Did you complete the repair?

—

Go to Step 20

—

15

1.

Test the brake pedal 2 switch signal circuit
between the ECM (pin 65 of B-234 connector)
and the brake pedal 2 switch (pin 3 of B-66
connector) for the following conditions:

• An open circuit
• A short to battery or ignition voltage
• High resistance

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 20

Go to Step 17

16

1.

Turn OFF the ignition.

2.

Disconnect the brake pedal switch harness
connector.

3.

Inspect for an intermittent and for poor
connections at the harness connector of the
brake pedal switch (pins 1, 2, 3 and 4 of B-66
connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 20

Go to Step 18

17

1.

Turn OFF the ignition.

2.

Disconnect the ECM harness connector.

3.

Inspect for an intermittent and for poor
connections on the brake switch circuits at the
harness connector of the ECM (pins 30 and
65 of B-234 connector).

4.

Repair the connection(s) as necessary.

Did you find and correct the condition?

—

Go to Step 20

Go to Step 19

18

Replace brake pedal switch.  Refer to Brake Switch
Replacement in this section.

Did you complete the replacement?

—

Go to Step 20

—

Step

Action

Value(s)

Yes

No