Dodge Ram Truck 1500-2500-3500. Manual — part 1181

P0172-FUEL SYSTEM 1/1 RICH (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 purge fuel multiplier and the result
is below a certain value for 30 seconds over 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

O2 SENSOR

(K41) O2 SENSOR 1/1 SIGNAL CIRCUIT OPEN

(K41) O2 SENSOR 1/1 SIGNAL CIRCUIT SHORTED TO VOLTAGE

1/1 O2 SENSOR HEATER OPERATION

EVAP SYSTEM OPERATION

TP SENSOR VOLTAGE GREATER THAN 0.92 OF A VOLT WITH THROTTLE CLOSED

TP SENSOR

FUEL FILTER/PRESSURE REGULATOR

MAP SENSOR

ECT SENSOR

ENGINE MECHANICAL CONDITION

PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).

Diagnostic Test

1.

GOOD TRIP EQUAL TO ZERO

NOTE: Check for contaminates that may have damaged the O2 Sensor: contaminated fuel, unapproved sil-
icone, oil and coolant.
Ignition on, engine not running.

With the scan tool, read DTCs and record the related Freeze Frame data.

NOTE: Any O2 Sensor, TPS, ECT, MAP, or EVAP DTCs must be repaired before continuing.

Is the Good Trip Counter displayed and equal to zero?

Yes

>> Go To 2

No

>> Refer to the INTERMITTENT CONDITION Symptom (Diagnostic Procedure).

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

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ENGINE - ELECTRICAL DIAGNOSTICS - SRT-10

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P0172-FUEL SYSTEM 1/1 RICH (CONTINUED)

2.

CHECKING FUEL PRESSURE

Turn the ignition off.

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.
Install a fuel pressure gauge.

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 379 KPa +/- 14 KPa (55 psi +/- 2 psi).

Choose a conclusion that best matches your fuel pressure reading.

Within Specification

Go To 3

Above Specification

Replace the fuel filter/pressure regulator.

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

CAUTION: Stop All Actuations.

3.

O2 SENSOR OPERATION

Ignition on, engine not running.

With the scan tool, monitor all of the O2 Sensor voltage readings.

Is the voltage above 4.5 volts for all of the O2 Sensors?

Yes

>> Go To 4

No

>> Go To 11

4.

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 between 4 and 5 volts.
Ignition on, engine not running.

With the scan tool, actuate the O2 Heater Test.

With the scan tool, monitor O2 Sensor voltage for at least 2 minutes.

Does the voltage stay above 4.5 volts?

Yes

>> Replace the O2 Sensor that had the voltage reading above 4.5 volts.

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

No

>> Go To 5

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P0172-FUEL SYSTEM 1/1 RICH (CONTINUED)

5.

EVAP SYSTEM OPERATION

NOTE: The engine must be at operating temperature and in closed loop to perform this test.
Start the engine.

WARNING: When the engine is operating, do not stand in a direct line with the fan. Do not put your hands
near the pulleys, belts, or fan. Do not wear loose clothing.
Allow the engine to reach normal operating temperature.

With the scan tool select System Tests, perform the Purge Vapors Test.

Observe the Short Term Adaptive value and press 3 to flow.

NOTE: Short Term Adaptive value change.

Did the Short Term Adaptive value change?

Yes

>> Go To 6

No

>> Refer to the Driveability category and perform the appropriate Diagnostic test.

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

6.

TP SENSOR VOLTAGE GREATER THAN 0.92 OF A VOLT WITH THROTTLE CLOSED

Ignition on, engine not running.

With the scan tool, read TP Sensor voltage.

NOTE: The throttle must be against the stop.

Is the voltage 0.92 of a volt or less with the Throttle closed?

Yes

>> Go To 7

No

>> Check for a binding throttle condition. If OK, replace the Throttle Position Sensor.

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

7.

TP SENSOR SWEEP

With the scan tool, read the TP Sensor voltage.

While monitoring the scan tool, slowly open and close the throttle.

Does the voltage increase and decrease smoothly?

Yes

>> Go To 8

No

>> Replace the Throttle Position Sensor.

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

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P0172-FUEL SYSTEM 1/1 RICH (CONTINUED)

8.

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 in Sensors, read the MAP Sensor vacuum value.

Is the scan tool reading within 1

(

of the Vacuum Gauge reading?

Yes

>> Go To 9

No

>> Replace the MAP Sensor.

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

NOTE: Remove the vacuum gauge before continuing.

9.

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 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 Engine Coolant Temperature value. The temp value change should be a
smooth transition from start up to normal operating temp 82°C (180°F). The value should reach at least 82°C
(180°F).

Did the Engine Coolant Temperature value increase smoothly and reach at least 82°C?

Yes

>> Go To 10

No

>> Replace the Engine Coolant Temperature Sensor.

Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

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ENGINE - ELECTRICAL DIAGNOSTICS - SRT-10

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