GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2000 🢒 S/T Isuzu - 4WD 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4L60-E 🢒 DTC P0172 Fuel Trim System Rich

System Description

In order to provide the best possible combination of driveability, fuel economy, and emission control, a Closed Loop air and fuel metering system is used. While in a Closed Loop, the powertrain control module (PCM) monitors the oxygen sensor signal voltage. The PCM adjusts fuel delivery based on signal voltage. The Long and Short Term fuel trim (FT) values will indicate a change made to the fuel delivery. The ideal FT values are around 0 percent. Whenever the oxygen sensor signal is indicating a Rich condition, the PCM will subtract fuel resulting in FT values from 0 to -100 percent. Whenever the exhaust emissions reach an excessive level due to a rich condition, DTC P0172 will set.

Conditions for Running the DTC
    • No active MAP DTCs
    • No active IAT DTCs
    • No active ECT DTCs
    • No active TP DTCs
    • No active oxygen sensor DTCs
    • No active injector control DTCs
    • No active misfire DTCs
    • No active knock sensor DTCs
    • No active CKP DTCs
    • No active CMP DTCs
    • No active EVAP DTCs
    • No active VSS DTCs
    • No active IAC DTCs
    • No active PCM memory DTCs
    • Intake air temperature (IAT) is between -25°C (-13°F) and 115°C (175°F)
    • Engine coolant temperature is between 60°C (140°F) and 115°C (239°F)
    • Engine speed is between 850 RPM and 3,400 RPM
    • Vehicle speed is below 82 mph (132 km/h)
    • MAP is above 26 kPa
    • BARO is above 72 kPa
    • The fuel level is above 10 percent

Conditions for Setting the DTC
    • Fuel trim index is below 75 (-40 percent).
    • Above conditions present for over 16 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.
    • The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame and Failure Records.

Conditions for Clearing the MIL/DTC
    • The MIL will turn off after 3 consecutive ignition cycles in which the diagnostic runs without a fault.
    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • Use a scan tool to clear the DTCs.

Diagnostic Aids
    • Inspect for a poor connection at the PCM. Inspect harness connectors for the following conditions:
       - Backed out terminals
       - Improper mating
       - Broken locks
       - Improperly formed or damaged terminals
       - Poor terminal to wire connection
    • Inspect for a damaged harness. If the harness appears to be OK, observe the O2S 1 display on the scan tool while moving the connectors and wiring harness related to the engine harness. A change in the display will indicate the location of the fault.

Test Description

The numbers below refer to the step numbers on the diagnostic table:

  1. A more negative value indicates the PCM is leaning the fuel mixture (rich condition).

    2.

  2. This step checks for a fuel delivery concern.

Step

Action

Values

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: : If any DTCs are set other than P0172, refer to those DTCs before proceeding with this diagnostic.

  1. Install the scan tool.
  2. Idle the engine in closed loop at normal operating temperature.
  3. With the scan tool, observe the Long Term FT.

Does the Long Term FT value read closer to the specified value?

-14 %

Go to Step 4

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Review the Freeze Frame and Failure Records for this DTC and observe the parameters.
  3. Turn OFF the ignition for 15 seconds.
  4. Start the engine.
  5. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, and as close to the conditions recorded in Freeze Frame or Failure Records as possible.
  6. Select DTC and the Specific DTC function.
  7. Enter the DTC number which was set.

Does the scan tool indicate that this diagnostic failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

Visually and physically check the following items:

    • The air filter for being restricted.
    • The air intake duct for being collapsed or restricted.
    • The MAF sensor for proper installation and any screen blockage.
    • IAC: If a low or unsteady idle is being experienced.
    • Check for throttle body coking or objects blocking the IAC passages.
    • O2S 1 electrical connector for contact with the exhaust system.
    • Check the fuel pressure regulator for proper operation or a slow diaphragm leak. Refer to Fuel System Diagnosis .
    • Excessive fuel in the crankcase. Change oil if necessary.

Did any of the above checks isolate a condition requiring repair?

--

Go to Step 9

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Turn ON the ignition with the engine OFF.
  3. The fuel pump should run for about 2 seconds.
  4. It may be necessary to cycle the ignition ON more than once in order to obtain maximum pressure.
  5. Monitor the fuel pressure with the fuel pump running. The fuel pressure should be within the first specified value range.
  6. When the fuel pump stops, the fuel pressure may vary slightly, then it should hold steady within the second value range.

Is fuel pressure within the specified value ranges and does it hold?

248-325

kPa (41-47 psi)

Go to Step 6

Go to Step 12

6

Perform the Fuel Injector Balance Test .

Was an injector problem found?

--

Go to Step 10

Go to Step 7

7

Perform the Evaporative Emission Control System Diagnosis .

Was a problem found?

--

Go to Step 8

Go to Diagnostic Aids

8
  1. Repair the EVAP System.
  2. Use the Fuel Trim Reset function on the scan tool.
  3. Operate the vehicle in closed loop while monitoring the Long Term FT display.
  4. The Long Term FT should increase above the specified value.

Is the Long Term FT value closer to 0 percent than the specified value?

-14 %

Go to Step 11

Go to Step 4

9
  1. Repair the items found in Step 4.
  2. Use the Fuel Trim Reset function on the scan tool.
  3. Operate the vehicle in closed loop while monitoring the Long Term FT display.
  4. The Long Term FT value should increase above the specified value.

Is the Long Term FT value closer to 0 percent than the specified value?

-14 %

Go to Step 11

Go to Step 5

10
  1. Replace the fuel injector. Refer to Fuel Injector Replacement .
  2. Use the Fuel Trim Reset function on the scan tool.
  3. Operate the vehicle in closed loop while monitoring the Long Term FT display.
  4. The Long Term FT value should increase above the specified value.

Is the Long Term FT value closer to 0 percent than the specified value?

-14 %

Go to Step 11

Go to Step 5

11

Rich condition is not present.

Does a driveability symptom still exist?

 

Go to Symptoms

Go to Step 13

12

Refer to Fuel System Diagnosis .

Is the action complete?

--

Go to Step 13

--

13
  1. Use a scan tool, to clear the DTCs.
  2. Operate the vehicle, within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC reset?

--

System OK

Go to Step 2