check engine ISUZU TF SERIES 2004 Workshop Manual

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-117
CIRCUIT DESCRIPTION
When the ignition switch is turned “ON," the Engine
Control Module (ECM) will turn “ON" the in-tank fuel
pump. The in-tank fuel pump will remain “ON" as long
as the engine is cranking or running and the ECM is
receiving 58X crankshaft position pulses. If there are no
58X crankshaft position pulses, the ECM will turn the
in-tank fuel pump “OFF" 2 seconds after the ignition
switch is turned “ON" or 2 seconds after the engine
stops running.
The in-tank fuel pump is an electric pump within an
integral reservoir. The in-tank fuel pump supplies fuel
through an in-line fuel filter to the fuel rail assembly. The
fuel pump is designed to provide fuel at a pressure
above the pressure needed by the fuel injectors. A fuel
pressure regulator, attached to the fuel rail, keeps the
fuel available to the fuel injectors at a regulated
pressure. Unused fuel is returned to the fuel tank by a
separate fuel return line.
TEST DESCRIPTION
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. Connect the fuel pressure gauge to the fuel feed line
as shown in the fuel system illustration. Wrap a shop
towel around the fuel pressure connection in order to
absorb any fuel leakage that may occur when
installing the fuel pressure gauge. With the ignition
switch “ON" and the fuel pump running, the fuel
pressure indicated by the fuel pressure gauge
should be 333-376 kPa (3.4-3.8 kg/cm
2 / 48-55 psi).
This pressure is controlled by the amount o
f
pressure the spring inside the fuel pressure regulator
can provide.
3. A fuel system that cannot maintain a constant fuel
pressure has a leak in one or more of the following
areas:
 The fuel pump check valve.
 The fuel pump flex line.
 The valve or valve seat within the fuel pressure
regulator.
 The fuel injector(s).
4. Fuel pressure that drops off during acceleration,
cruise, or hard cornering may case a lean condition.
A lean condition can cause a loss of power, surging,
or misfire. A lean condition can be diagnosed using
a Tech 1 Tech 2. If an extremely lean condition
occurs, the oxygen sensor(s) will stop toggling. The
oxygen sensor output voltage(s) will drop below 500
mV. Also, the fuel injector pulse width will increase.

Important: Make sure the fuel system is not operating
in the “Fuel Cut-Off Mode."
When the engine is at idle, the manifold pressure is
low (high vacuum). This low pressure (high vacuum)
is applied to the fuel pressure regulator diaphragm.
The low pressure (high vacuum) will offset the
pressure being applied to the fuel pressure regulato
r
diaphragm by the spring inside the fuel pressure
regulator. When this happens, the result is lower fuel
pressure. The fuel pressure at idle will vary slightly
as the barometric pressure changes, but the fuel
pressure at idle should always be less than the fuel
pressure noted in step 2 with the engine “OFF."
16.Check the spark plug associated with a particula
r
fuel injector for fouling or saturation in order to
determine if that particular fuel injector is leaking. I
f
checking the spark plug associated with a particular
fuel injector for fouling or saturation does no
t
determine that a particular fuel injector is leaking,
use the following procedure:
 Remove the fuel rail, but leave the fuel lines and
injectors connected to the fuel rail. Refer to Fue
l
Rail Assembly in On-Vehicle Service.
 Lift the fuel rail just enough to leave the fuel
injector nozzles in the fuel injector ports.
CAUTION: In order to reduce the risk of fire and
personal injury that may result from fuel spraying
on the engine, verify that the fuel rail is positioned
over the fuel injector ports and verify that the fuel
injector retaining clips are intact.
 Pressurize the fuel system by connecting a 10
amp fused jumper between B+ and the fuel pump
relay connector.

Visually and physically inspect the fuel injector
nozzles for leaks.
17. A rich condition may result from the fuel pressure
being above 376 kPa (55 psi). A rich condition may
cause a DTC P0132 or a DTC P0172 to set.
Driveability conditions associated with rich conditions
can include hard starting (followed by black smoke)
and a strong sulfur smell in the exhaust.
20.This test determines if the high fuel pressure is due
to a restricted fuel return line or if the high fuel
pressure is due to a faulty fuel pressure regulator.
21.A lean condition may result from fuel pressure belo
w
333 kPa (48 psi). A lean condition may cause a DTC
P0131 or a DTC P0171 to set. Driveability conditions
associated with lean conditions can include hard
starting (when the engine is cold ), hesitation, poo
r
driveability, lack of power, surging , and misfiring.

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-119
Fuel System Diagnosis

Step Action Value(s) YES NO
1
Was the “On-Board Diagnostic (OBD) System Check"
performed? — Go to Step 2 Go to OBD
System Check
2
1. Turn the ignition “OFF."
2. Turn the air conditioning system “OFF."
3. Relieve fuel system pressure and install the fuel
pressure gauge.
Refer to 6E-118 FUEL GAUGE INSTALLATION
4. Turn the ignition “ON."
NOTE: The fuel pump will run for approximately 2
seconds. Use the Tech 2 to command the fuel
pump “ON".
5. Observe the fuel pressure indicated by the fuel
pressure gauge with the fuel pump running.
Is the fuel pressure within the specified limits? 290-376 kPa
(42-55 psi) Go to Step 3 Go to Step 17
3
The fuel pressure will drop when the fuel pump stops
running, then it should stabilize and remain constant.
Does the fuel pressure indicated by the fuel pressure
gauge remain constant? — Go to Step 4 Go to Step 12
4
1. When the vehicle is at normal operation
temperature, turn the ignition “ON" to build fuel
pressure and observe the measurement on the
gauge.
2. Start the engine and observe the fuel pressure
gauge.
Did the reading drop by the amount specified after the
engine was started? 21-105 kPa
(3-15 psi) Go to Step 5 Go to Step 9
5
Is fuel pressure dropping off during acceleration,
cruise, or hard cornering? — Go to Step 6 Check for
improper fuel
6 Visually and physically inspect the following items for
a restriction:
 The in-line fuel filter.
 The fuel feed line.
Was a restriction found? — Verify repair Go to Step 7
7 Remove the fuel tank and visually and physically
inspect the following items:
 The fuel pump strainer for a restriction.
 The fuel line for a leak.
 Verify that the correct fuel pump is in the vehicle.
Was a problem found in any of these areas? — Verify repair Go to Step 8

6E-122 3.5L ENGINE DRIVEABILITY AND EMISSIONS
A/C SYSTEM CIRCUIT DIAGNOSIS



RTW36EMF000101

CIRCUIT DESCRIPTION
When air conditioning and blower fan are selected, and
if the system has a sufficient refrigerant charge, a
12-volt signal is supplied to the A/C request input of the
Engine Control Module (ECM). The A/C request signal
may be temporarily canceled during system operation
by the electronic thermostat in the evaporator case. The
electronic thermostat may intermittently remove the
control circuit ground for the A/C thermostat relay to
prevent the evaporator from forming ice. When the A/C
request signal is received by the ECM, the ECM
supplies a ground from the compressor clutch relay i
f
the engine operating conditions are within acceptable
ranges. With the A/C compressor relay energized,
voltage is supplied to the compressor clutch coil.
The ECM will enable the compressor clutch to engage
whenever A/C has been selected with the engine
running, unless any of the following conditions are
present:

 The A/C request switch is "Off".
 The engine speed is lower than 550rpm or greate
r
than 6375rpm.
 The engine coolant temperature is greater than
120
.
DIAGNOSTIC AIDS
To diagnose an the intermittent fault, check for the
following conditions:
 Poor connection at the ECM–Inspect connections fo
r
backed-out terminals, improper mating, broken locks,
improperly formed or damaged terminals, and poo
r
terminal-to-wire connection.
 Damaged harness–Inspect the wiring harness fo
r
damage. If the harness appears to OK, observe the
A/C clutch while moving connectors and wiring
harnesses related to the A/C. A sudden clutch
malfunction will indicate the source of the intermitten
t
fault.

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-123
A/C CLUTCH DIAGNOSIS
This chart should be used for diagnosing the electrical
portion of the A/C compressor clutch circuit. A Tech 2
will be used in diagnosing the system. The Tech 2 has
the ability to read the A/C request input to the ECM. The
Tech 2 can display when the ECM has commanded the
A/C clutch “ON." The Tech 2 should have the ability to
override the A/C request signal and energize the A/C
compressor relay.




A/C Clutch Control Circuit Diagnosis
Step Action Value (s) Yes No
1
Was the "On-Board Diagnostic (OBD) System Check"
performed?
- Go to Step 2 Go to On Board
Diagnostic (OBD)
System Check
2
Are the A/C setting conditions met?
- Go to Step 3 Set the setting
condition and Go
to Step 3
3
Is the A/C compressor worked properly?
- Diagnosis
completed Go to Step 4
4
Does the blower motor operate?
- Go to Step 6 Go to Step 5
5
Repair the blower motor circuit.
Is the action complete?
- Verify repair -
6
1. Using the Tech 2, ignition "On" and engine "On".
2. Select the "Miscellaneous Test" and perform the
"A/C Clutch Relay" in the "Relays".
3. Operate the Tech 2 in accordance with procedure.
Was the A/C compressor magnet clutch engaged,
when the Tech 2 is operated?
- Go to Step 15 Go to Step 7
7
Check the "A/C" fuse (10A). If the fuse is burnt out,
repair as necessary.
Was the problem found?
- Verify repair Go to Step 8

6E-124 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Step Action Value (s) Yes No
8
Check for poor/faulty connection at the A/C
compressor, A/C compressor relay or ECM connector.
If a poor/faulty connection is found, repair as
necessary.
Was the problem found?
E-2


X-14







E-61(B)



- Verify repair Go to Step 9
9
 Using the DVM and check the A/C compressor relay.
1. Ignition "Off", engine "Off".
2. Remove the A/C compressor relay from the relay
box.
3. Check the relay coil.
Was the DVM indicated specified value?
X-14






Approximately
140

Go to Step 10 Replace A/C
compressor relay
and verify repair
10
Using the DVM and check the A/C compressor relay
power supply circuit.
1. Ignition "On", engine "Off".
2. Remove the A/C compressor relay from the relay
box.
3. Check the circuit for open or short to ground circuit.
Was the DVM indicated specified value?
X-14





VV

10 – 14.5V Go to Step 12 Go to Step 11
11
Repair the open or short to ground circuit between the
"A/C" fuse (10A) and A/C compressor relay.
Is the action complete?
- Verify repair -

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-125
Step Action Value (s) Yes No
12
 Using the DVM and check the A/C compressor relay
ground circuit.
1. Ignition "Off", engine "Off".
2. Disconnect the ECM connector.
3. Remove the A/C compressor relay from the relay
box.
4. Check the circuit for open or short to ground circuit.
Was the problem found?
E-61(B)
X-14









- Repair faulty
harness and
verify repair Go to Step 13
13
Using the DVM and check the A/C magnet clutch
power supply circuit.
1. Using the Tech 2, ignition "On" and engine "Off".
2. Select the "Miscellaneous Test" and perform the
"A/C Clutch Relay" in the "Relays".
3. Operate the Tech 2 in accordance with procedure.
4. Disconnect the A/C clutch connector. Check the
circuit for open or short to ground circuit.
Was the DVM indicated specified value?
E-2
V



10 – 14.5V Go to Step 27 Go to Step 14
14
Repair the open or short to ground circuit between the
A/C compressor relay and A/C magnet clutch.
Is the action complete?
E-2X-14






- Verify repair -

6E-126 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Step Action Value (s) Yes No
15
Check for poor/faulty connection at the thermo relay,
triple pressure switch, thermostat or ECM connector. If
a poor/faulty connection is found, repair as necessary.
Was the problem found?
E-61(B)
X-15







C-24C-55









- Verify repair Go to Step 16
16
 Using the DVM and check the thermo relay.
1. Ignition "Off", engine "Off".
2. Remove the thermo relay from the relay box.
3. Check the relay coil.
Was the DVM indicated specified value?
X-15






Approximately
140

Go to Step 17 Replace thermo
relay and verify
repair
17
 Using the DVM and check the thermo relay power
supply circuit.
1. Ignition "On", engine "Off".
2. Remove the thermo relay from the relay box.
3. Check the circuit for open or short to ground circuit.
Was the DVM indicated specified value?
X-15





VV

10 – 14.5V Go to Step 19 Go to Step 18
18
Repair the open or short to ground circuit between the
"A/C" fuse (10A) and thermo relay.
Is the action complete?
- Verify repair -

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-127
Step Action Value (s) Yes No
19
Using the DVM and check the triple pressure switch
circuit.
1. Ignition "On", engine "Off".
2. Turn "On" blower motor.
3. Disconnect the triple pressure switch connector.
4. Check the circuit for open or short to ground circuit.
Was the DVM indicated specified value?
C-24
V



10 – 14.5V Go to Step 21 Go to Step 20
20
Repair the open or short to ground circuit between the
thermo relay and triple pressure switch.
Is the action complete?
C-24
X-15





- Verify repair -
21
Using the DVM and check the triple pressure switch.
1. Ignition "Off", engine "Off".
2. Disconnect the triple pressure switch connector.
3. Check the switch.
Was the switch closed?
Triple Pressure
SW






- Go to Step 23 Go to Step 22
22
Replace the triple pressure switch.
Is the action complete?
- Verify repair -

6E-128 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Step Action Value (s) Yes No
23
Using the DVM and check the thermostat circuit.
1. Ignition "On", engine "Off".
2. Turn "On" blower motor.
3. Disconnect the triple pressure switch connector.
4. Check the circuit for open or short to ground circuit.
Was the DVM indicated specified value?
C-55
V



10 – 14.5V Go to Step 25 Go to Step 24
24
Repair the open or short to ground circuit between the
triple pressure switch and thermostat.
Is the action complete?
C-55C-24



- Verify repair -
25
Replace the thermostat.
Is the action complete?
- Verify repair -
26
Using the DVM and check the thermo relay input
circuit.
1. Ignition "Off", engine "Off".
2. Disconnect the ECM connector.
3. Remove the thermo relay from the relay box.
4. Check the circuit for open or short to ground circuit.
Was the problem found?
E-61(B)
X-15










- Repair faulty
harness and
verify repair Go to Step 28
27
Replace the A/C compressor.
Was the problem solved?
- Verify repair -

6E-130 3.5L ENGINE DRIVEABILITY AND EMISSIONS
ECM DIAGNOSTIC TROUBLE CODES (DTC)

DTC Type A

Emission related.

Requests illumination of the MIL (Malfunction Indicator Lamp = Check Engine Lamp) of the first trip with a fail.

Stores a history DTC on the first trip with a fail.

Stores a freeze frame (If empty).

Stores a fail record.

Updates the fail record each time the diagnostic test fails.

DTC Type B

Emission related.

"Armed" after one trip with fail.

"Disarmed" after one trip with a pass.

Requests illumination of the MIL on the second consecutive trip with a fail.

Store a history DTC on the second consecutive trip with a fail. (The DTC will be armed after the first fail.)

Stores a freeze frame on the second consecutive trip with a fail (If empty).

Stores a fail record when the first test fails (not dependent on consecutive trip).

Updates the fail record each time the diagnostic test fails.

DTC Type D

Non emission related.

Does not request illumination of any lamp.

Stores a history DTC on the first trip with a fail.

Does not store a freeze frame.

Stores fail record when test fails.

Updates the fail record each time the diagnostic test fails.