2004 ISUZU TF SERIES fuel pressure

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-120 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Step Action Value(s) YES NO
8 Replace the fuel pump.
Is the action complete? — Verify repair —
9
1. Disconnect the vacuum hose from the fuel
pressure regulator.
2. With the engine idling, apply 12-14 inches of
vacuum to the fuel pressure regulator.
Does the fuel pressure indicated by the fuel pressure
gauge drop by the amount specified? 21-105 kPa
(3-15 psi) Go to Step 10 Go to Step 11
10 Locate and repair the loss of vacuum to the fuel
pressure regulator.
Is the action complete? — Verify repair —
11 Replace the fuel pressure regulator.
Is the action complete? — Verify repair —
12
1. Run the fuel pump with the Tech 2.
2. After pressure has built up, turn off the pump and
clamp the supply hose shut with suitable locking
pliers.
Does the fuel pressure indicated by the fuel pressure
gauge remain constant? — Go to Step 13 Go to Step 15
13 Visually inspect the fuel supply line and repair any
leaks.
Was a problem found? — Verify repair Go to Step 14
14 Remove the fuel tank and inspect for leaky hose or
in-tank fuel line.
Was a problem found? — Verify repair Go to Step 8
15
1. If the pliers are still clamped to the fuel supply
hose, remove the locking pliers.
2. With suitable locking pliers, clamp the fuel return
line to prevent fuel from returning to the fuel tank.
3. Run the fuel pump with the Tech 2.
4. After pressure has built up, remove power to the
pump.
Does the fuel pressure indicated by the fuel pressure
gauge remain constant? — Go to Step 11 Go to Step 16
16 Locate and replace any leaking fuel injector(s).
Is the action complete? — Verify repair —
17
Is the fuel pressure indicated by the fuel pressure
gauge above the specified limit? 376 kPa (55
psi) Go to Step 18 Go to Step 21

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-121
Step Action Value(s) YES NO
18
1. Relieve the fuel pressure. Refer to the Fuel
Pressure Relief.
2. Disconnect the fuel return line from the fuel rail.
3. Attach a length of flexible hose to the fuel rail
return outlet passage.
4. Place the open end of the flexible hose into an
approved gasoline container.
5. Run the fuel pump with the Tech 2.
6. 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 19 Go to Step 20
19 Locate and correct the restriction in the fuel return
line.
Is the action complete? — Verify repair —
20 Visually and physically inspect the fuel rail outlet
passages for a restriction.
Was a restriction found? — Verify repair Go to Step 11
21
Is the fuel pressure indicated by the fuel pressure
gauge above the specified value? 0 kPa (0 psi) Go to Step 22 Go to Step 23
22
1. Command the fuel pump “ON" with the Tech 2.
2. Using suitable pliers which will not damage the fuel
hose, gradually apply pressure with the pliers to
pinch the flexible fuel return hose closed.
CAUTION: Do not let the fuel pressure exceed the
second specified value.
Does the fuel pressure indicated by the fuel pressure
gauge rise above the first specified value? 376 kPa (55
psi). 414 kPa
(60 psi). Go to Step 11 Go to Step 7
23
1. Command the fuel pump “ON" with the Tech 2.
2. Remove the fuel filler cap and listen for the sound
of the fuel pump running.
3. Turn the pump off.
Was the fuel pump running? — Go to Step 7 Go to Fuel
System
Electrical Test
Chart

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-133
Flash
Code Code Type DTC Name DTC Setting Condition Fail-Safe (Back Up) Recovery Condition Related Failure Parts Related
ECM Pin
No. Related
Multiple
DTC
P0131 A O2 Sensor Circuit Low Voltage
(Bank 1 Sensor 1) B21/
B22 P0171/
P1171/
P1172 P0151 A O2 Sensor Circuit Low Voltage
(Bank 2 Sensor 1) 1. No DTC relating to ECT sensor, CMP sensor,
CKP sensor, VSS, injector control circuit,
ignition control circuit and O2 sensor circuit no
activity (bank 1 & 2).
2. Engine speed is between 1000rpm and
4000rpm.
3. Engine coolant temperature is between 70
C
and 110
C.
4. Vehicle speed is between 0km/h and
120km/h.
5. Engine load is between 80% and 160%.
6. Throttle position fluctuation is below 0.28V.
7. O2 sensor bank 1 or bank 2 output voltage is
more than 400mV for 50 seconds. "Open Loop" fuel control. O2 sensor bank 1 or bank 2
output voltage is below 400mV
for 50 seconds. 1. Sensor harness open or short to ground
circuit.
2. O2 sensor malfunction.
3. MAF sensor output is incorrect.
4. Air intake line malfunction.
5. IAC valve malfunction.
6. Low fuel pressure.
7. Injector malfunction.
8. ECM malfunction.
B23/
B24 P0174/
P1171/
P1172 P0132 A O2 Sensor Circuit High Voltage
(Bank 1 Sensor 1) B21/
B22 P0172 P0152 A O2 Sensor Circuit High Voltage
(Bank 2 Sensor 1) 1. No DTC relating to ECT sensor, CMP sensor,
CKP sensor, VSS, injector control circuit,
ignition control circuit and O2 sensor circuit no
activity (bank 1 & 2).
2. Engine speed is between 1000rpm and
4000rpm.
3. Engine coolant temperature is between 70
C
and 110
C.
4. Vehicle speed is between 0km/h and
120km/h.
5. Engine load is between 80% and 160%.
6. Throttle position fluctuation is below 0.28V.
7. O2 sensor bank 1 or bank 2 output voltage is
below 600mV for 50 seconds. "Open Loop" fuel control. O2 sensor bank 1 or bank 2
output voltage is more than
600mV for 50 seconds. 1. Sensor harness open or short to ground
circuit.
2. O2 sensor malfunction.
3. MAF sensor output is incorrect.
4. Air intake line malfunction.
5. AC valve malfunction.
6. Low fuel pressure.
7. Injector malfunction.
8. EVAP purge solenoid valve malfunction.
9. Ignition system malfunction.
10. Spark plug malfunction.
11. ECM malfunction. B23/
B24 P0175 P0134 A O2 Sensor Circuit No Activity
Detected (Bank 1 Sensor 1) B21/
B22 -
15

P0154 A O2 Sensor Circuit No Activity
Detected (Bank 2 Sensor 1) 1.No DTC relating to MAF sensor, ECT sensor,
CMP sensor, CKP sensor, VSS, injector
control circuit and ignition control circuit.
2. Engine coolant temperature is more than
70
C.
3. Vehicle speed is more than 60km/h.
4. O2 sensor bank 1 or bank 2 output voltage is
between 350mV and 600mV. "Open Loop" fuel control. O2 sensor bank 1 or bank 2
output voltage is below 0.35mV
consecutively.
OR
O2 sensor bank 1 or bank 2
output voltage is more than
600mV consecutively. 1. O2 sensor malfunction.
2. ECM malfunction.
B23/
B24 -

6E-134 3.5L ENGINE DRIVEABILITY AND EMISSIONS Flash
Code Code Type DTC Name DTC Setting Condition Fail-Safe (Back Up) Recovery Condition Related Failure Parts Related
ECM Pin
No. Related
Multiple
DTC
P0171 B O2 Sensor System Too Lean
(Bank 1) - -
44
P0174 B O2 Sensor System Too Lean
(Bank 2) 1. No DTC relating to MAF sensor, IAT sensor,
ECT sensor, TPS, CMP sensor, CKP sensor,
VSS, injector control circuit, ignition control
circuit, O2 sensor circuit low voltage & high
voltage (bank 1 & 2) and O2 sensor circuit no
activity (bank 1 & 2).
2. Engine speed is more than 600rpm.
3. Intake air temperature is more than 50
C.
4. Engine coolant temperature is between 35
C
and 120
C.
5. Engine load is more than 20.
6. EVAP purge solenoid valve on-duty is below
100%.
7. Air-fuel ratio correction volume is more than
150% for 20 seconds. No fail-safe function. Air fuel ratio correction volume
is between 50% and 150% for
5 seconds. 1. Sensor harness open or short to ground
circuit.
2. O2 sensor malfunction.
3. MAF sensor output is incorrect.
4. Air intake line malfunction.
5. IAC valve malfunction.
6. Low fuel pressure.
7. Injector malfunction.
8. ECM malfunction.
- -
P0172 B O2 Sensor System Too Rich
(Bank 1) - -
45
P0175 B O2 Sensor System Too Rich
(Bank 2) 1. No DTC relating to MAF sensor, IAT sensor,
ECT sensor, TPS, CMP sensor, CKP sensor,
VSS, injector control circuit, ignition control
circuit, O2 sensor circuit low voltage & high
voltage (bank 1 & 2) and O2 sensor circuit no
activity (bank 1 & 2).
2. Engine speed is more than 600rpm.
3. Intake air temperature is more than 50
C.
4. Engine coolant temperature is between 35
C
and 120
C.
5. Engine load is more than 20.
6. EVAP purge solenoid valve on-duty is below
100%.
7. Air-fuel ratio correction volume is below 50%
for 20 seconds. No fail-safe function. Air fuel ratio correction volume
is between 50% and 150% for
5 seconds. 1. Sensor harness open or short to ground
circuit.
2. O2 sensor malfunction.
3. MAF sensor output is incorrect.
4. Air intake line malfunction.
5. AC valve malfunction.
6. Low fuel pressure.
7. Injector malfunction.
8. EVAP purge solenoid valve malfunction.
9. Ignition system malfunction.
10. Spark plug malfunction.
11. ECM malfunction. - -

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-135
Flash
Code Code Type DTC Name DTC Setting Condition Fail-Safe (Back Up) Recovery Condition Related Failure Parts Related
ECM Pin
No. Related
Multiple
DTC
P1171 D Fuel Supply System Lean
During Power Enrichment
(Bank 1) B21/
B22/
-
44
P1172 D Fuel Supply System Lean
During Power Enrichment
(Bank 2) 1. No DTC relating to MAF sensor, IAT sensor,
ECT sensor, TPS, CMP sensor, CKP sensor,
VSS, injector control circuit, ignition control
circuit, O2 sensor circuit low voltage & high
voltage (bank 1 & 2) and O2 sensor circuit no
activity (bank 1 & 2).
2. Engine speed is between 1000rpm and
6000rpm.
3. Intake air temperature is below 70
C.
4. Engine coolant temperature is between 30
C
and 120
C.
5. Engine load is between 150 and 255.
6. Throttle position output is more than 2.22V
and fluctuation is below 0.28V.
7. Except fuel cut operation.
8. O2 sensor output voltage below 250mV for 10
seconds. No fail-safe function.
O2 sensor output voltage is
more than 520mV for 5
seconds.
1. Sensor harness open or short to ground
circuit.
2. O2 sensor malfunction.
3. MAF sensor output is incorrect. 4. Air intake
line malfunction.
5. IAC valve malfunction.
6. Low fuel pressure.
7. Injector malfunction.
8. ECM malfunction.
B23/
B24 -
P0201 A Injector 1 Control Circuit
A36 - P0202 A Injector 2 Control Circuit
B3 - P0203 A Injector 3 Control Circuit
A35 - P0204 A Injector 4 Control Circuit
B4 - P0205 A Injector 5 Control Circuit
A34 -
31
P0206 A Injector 6 Control Circuit 1. No DTC relating to CMP sensor and CKP
sensor.
2. Under sequential injection.
3. Injection pulse is between 2.5ms and 7.5 ms.
4. Except fuel cut operation.
5. Engine speed is between 600rpm and
2000rpm.
6. 30 injection signals are not detected
consecutively. No fail-safe function. 30 injection signals are
detected consecutively. 1. Injector harness open circuit, short to ground
or short to voltage.
2. Injector malfunction.
3. ECM malfunction.
B5 -

6E-144 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Too low fuel pressure (poor fuel) will cause one or more of following DTCs to be set.





P0131 (Flash Code 15): O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)





P0151 (Flash Code 15): O2 Sensor Circuit Low Voltage (Bank 2 Sensor 1)





P0171 (Flash Code 44): O2 Sensor System Too Lean (Bank 1)





P0174 (Flash Code 44): O2 Sensor System Too Lean (Bank 2)





P1171 (Flash Code 44): Fuel Supply System Lean During Power Enrichment (Bank 1)





P1172 (Flash Code 44): Fuel Supply System Lean During Power Enrichment (Bank 2)

Too high fuel pressure (excessive fuel) will cause one or more of following DTCs to be set.





P0132 (Flash Code 15): O2 Sensor Circuit High Voltage (Bank1 Sensor 1)





P0152 (Flash Code 15): O2 Sensor Circuit High Voltage (Bank 2 Sensor 1)





P0172 (Flash Code 45): O2 Sensor System Too Rich (Bank 1)





P0175 (Flash Code 45): O2 Sensor System Too Rich (Bank 2)




RTW36ELF000101

6E-194 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Condition For Setting The DTC and Action Taken When The DTC Sets
Flash
Code Code Type DTC Name DTC Setting Condition Fail-Safe (Back Up)
P0131 A O2 Sensor Circuit Low
Voltage (Bank 1
Sensor 1) 15
P0151 A O2 Sensor Circuit Low
Voltage (Bank 2
Sensor 1) 1. No DTC relating to ECT sensor, CMP sensor, CKP sensor,
VSS, injector control circuit, ignition control circuit and O2
sensor circuit no activity (bank 1 & 2).
2. Engine speed is between 1000rpm and 4000rpm.
3. Engine coolant temperature is between 70
C and 110
C.
4. Vehicle speed is between 0km/h and 120km/h.
5. Engine load is between 80% and 160%.
6. Throttle position fluctuation is below 0.28V.
7. O2 sensor bank 1 or bank 2 output voltage is more than
400mV for 50 seconds. "Open Loop" fuel control.

CIRCUIT DESCRIPTION
The Engine Control Module (ECM) supplies a bias
voltage of about 450 mV between the heated oxygen
sensor (HO2S) signal high and signal low circuits. The
ECM constantly monitors the HO2S signal during
“closed loop" operation and compensates for a rich o
r
lean condition by decreasing or increasing injector pulse
width as necessary. If HO2S voltage remains
excessively low for an extended period of time, DTC
P0131 or P0151 will be set.
DIAGNOSTIC AIDS
Check for the following conditions:
 Heated oxygen sensor wiring – The sensor pigtail
may be routed incorrectly and contacting the exhaus
t
system.
 Poor ECM to engine block grounds.
 Fuel pressure – The system will go lean if pressure is
too low. The ECM can compensate for some
decrease. However, If fuel pressure is too low, a DTC
P0131 or P0151 may be set. Refer to 6E-116 Fue
l
System Diagnosis.

 Lean injector(s) – Perform “Injector Balance Test."
 Exhaust leaks – An exhaust leak may cause outside
air to be pulled into the exhaust gas stream past the
HO2S, causing the system to appear lean. Check fo
r
exhaust leaks that may cause a false lean condition
to be indicated.
 MAF sensor –The system can go lean if the MAF
sensor signal indicates an engine airflo
w
measurement that is not correct. Disconnect the MAF
sensor to see if the lean condition is corrected. If so,
replace the MAF sensor.
 Fuel contamination –Water, even in small amounts,
can be delivered to the fuel injectors. The water can
cause a lean exhaust to be indicated. Excessive
alcohol in the fuel can also cause this condition.
Refer to 6E-116 Fuel System Diagnosisfor the
procedure to check for fuel contamination.
 If none of the above conditions are present, replace
the affected HO2S.