Dodge Dakota (ND). Manual — part 670
P0174-FUEL SYSTEM 2/1 LEAN (CONTINUED)
For the Engine circuit diagram (Refer to 9 - ENGINE - SCHEMATICS AND DIAGRAMS).
For a complete wiring diagram Refer to Section 8W.
Theory of Operation
The fuel feedback system will maintain a stoiciometric fuel/air mixture, 14.7:1, by modifying the injector pulsewidth
according to the oxygen content of the exhaust gas. The PCM makes short term and long term fuel corrections to
maintain stoiciometric fuel/air ratio for best catalytic converter efficiency. Short term fuel correction is based on
upstream O2 sensor output and is designed for quick engine response. The long term fuel correction compensated
for variations in the engine specifications, sensor tolerances and component aging and is designed to correct rich
and lean conditions over a longer period of time.
•
When Monitored:
With the engine running in closed loop mode, the ambient/battery temperature above 20 deg. F and altitude
below 8500 ft.
•
Set Condition:
If the PCM multiplies short term compensation by long term adaptive and a certain percentage is exceeded for
two trips, a freeze frame is stored, the MIL illuminates and a trouble code is stored. Two Trip Fault. Three good
trips to turn off the MIL.
Possible Causes
RESTRICTED FUEL SUPPLY LINE
FUEL PUMP INLET STRAINER PLUGGED
FUEL PUMP MODULE
O2 SIGNAL CIRCUIT
O2 RETURN CIRCUIT
O2 SENSOR HEATER OPERATION
O2 SENSOR
MAP SENSOR OPERATION
ECT SENSOR OPERATION
ENGINE MECHANICAL
FUEL FILTER/PRESSURE REGULATOR (HIGH)
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.
ACTIVE DTC
Diagnose all other trouble codes before continuing.
NOTE: Check for contaminants that may have damaged an O2 Sensor: contaminated fuel, unapproved sil-
icone, oil and coolant.
Ignition on, engine not running.
With a scan tool, read DTCs.
Is the DTC active at this time?
Yes
>> Go To 2
No
>> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
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ENGINE ELECTRICAL DIAGNOSTICS
ND
P0174-FUEL SYSTEM 2/1 LEAN (CONTINUED)
2.
CHECKING FUEL PRESSURE
WARNING: The fuel system is under a constant pressure (even with the engine off). Before testing or ser-
vicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow
these instructions can result in personal injury or death.
Install a fuel pressure gauge to the fuel rail.
Ignition on, engine not running.
With the scan tool, actuate the ASD Fuel System test and observe the fuel pressure gauge.
NOTE: Fuel pressure specification is 407 KPa +/- 34 KPa (59 psi +/- 5 psi).
Turn the ignition off.
CAUTION: Stop All Actuations.
Choose a conclusion that best matches your fuel pressure reading.
Within Specification
Go To 3
Above Specification
Replace the fuel filter/pressure regulator.
Perform POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
Below Specification
Go To 12
3.
O2 SENSOR OPERATION
Start the engine.
Allow the engine to reach normal operating temperature.
NOTE: If one of the O2 Sensor’s Signal or Return circuit is shorted to ground the scan tool will display all
O2 Sensor voltage readings low. The O2 Sensor that is shorted to ground will display a voltage reading
near or at 0 volts.
NOTE: If one of the O2 Sensor Signal or Return circuits are shorted to voltage, the scan tool will display all
O2 Sensor voltage readings high.
NOTE: After the repairs have been made, verify proper O2 Sensor operation. If all the O2 Sensor voltage
readings have not returned to normal, follow the diagnostic procedure for the remaining O2 Sensors.
With the scan tool, monitor the 2/1 O2 Sensor voltage reading.
Is the voltage switching between 2.5 and 3.4 volts?
Yes
>> Go To 4
No
>> Go To 8
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ENGINE ELECTRICAL DIAGNOSTICS
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P0174-FUEL SYSTEM 2/1 LEAN (CONTINUED)
4.
2/1 O2 SENSOR HEATER OPERATION
Turn the ignition off.
NOTE: Wait a minimum of 10 minutes to allow the O2 Sensor to cool down before continuing the test. Allow
the O2 Sensor voltage to stabilize at 5.0 volts.
NOTE: Perform the following test on all O2 Sensors.
Ignition on, engine not running.
With a scan tool, actuate the 2/1 O2 Heater Test.
With the scan tool, monitor 2/1 O2 Sensor voltage for at least 2 minutes.
Does the voltage stay above 4.5 volts?
Yes
>> Replace the 2/1 O2 Sensor.
Perform POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
>> Go To 5
5.
MAP SENSOR OPERATION
Turn the ignition off.
Connect a Vacuum Gauge to a Manifold Vacuum source.
Start the engine.
Allow the engine to idle.
NOTE: If engine will not idle, maintain a constant RPM above idle.
With the scan tool, read the MAP Sensor vacuum value.
Is the scan tool reading within 1
(
of the Vacuum Gauge reading?
Yes
>> Go To 6
No
>> Replace the MAP Sensor.
Perform POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
6.
ECT SENSOR OPERATION
NOTE: For this test to be valid, the thermostat must be operating correctly.
NOTE: This test works best if performed on a cold engine (cold soak).
Ignition on, engine not running.
With the scan tool, read the Engine Coolant Temperature (ECT) Sensor value. If the engine was allowed to sit
overnight (cold soak), the temperature value should be a sensible value that is somewhere close to the ambient
temperature.
NOTE: If engine coolant temperature is above 82°C (180°F), allow the engine to cool until 65°C (150°F) is
reached.
Start the Engine.
During engine warm-up, monitor the ECT Sensor value. The temperature value change should be a smooth tran-
sition from start up to normal operating temperature 82°C (180°F). The value should reach at least 82°C (180°F).
Did the ECT value increase smoothly and did it reach at least 180°F (82°C)?
Yes
>> Go To 7
No
>> Replace the Engine Coolant Temperature Sensor.
Perform POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
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ENGINE ELECTRICAL DIAGNOSTICS
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P0174-FUEL SYSTEM 2/1 LEAN (CONTINUED)
7.
ENGINE MECHANICAL
Turn the ignition off.
Check for any of the following conditions/mechanical problems.
AIR INDUCTION SYSTEM - must be free from leaks.
ENGINE VACUUM - must be at least 13 inches in neutral
ENGINE VALVE TIMING - must be within specifications
ENGINE COMPRESSION - must be within specifications
ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks.
ENGINE PCV SYSTEM - must flow freely
TORQUE CONVERTER STALL SPEED - must be within specifications
POWER BRAKE BOOSTER - no internal vacuum leaks
FUEL - must be free of contamination
FUEL INJECTOR - plugged or restricted injector; control wire not connected to correct injector
Are there any engine mechanical problems?
Yes
>> Repair as necessary.
Perform POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No
>> Go To 11
8.
O2 SENSOR
Ignition on, engine not running.
Disconnect the 2/1 O2 Sensor harness connector.
With the scan tool, monitor the 2/1 O2 Sensor voltage.
O2 Sensor voltage should read 5.0 volts on the scan tool with the con-
nector disconnected.
Connect a jumper wire between the (K43) O2 Sensor 2/1 Signal circuit
and the (K902) O2 Return Upstream circuit in the O2 Sensor harness
connector.
NOTE: The voltage should drop from 5.0 volts to 2.5 volts with
the jumper wire in place.
Did the O2 Sensor voltage change from 5.0 volts to 2.5 volts
when the jumper wire was installed?
Yes
>> Replace the 2/1 O2 Sensor.
Perform POWERTRAIN VERIFICATION TEST. (Refer to 9
- ENGINE - STANDARD PROCEDURE)
No
>> Go To 9
NOTE: Remove the jumper wire before continuing.
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