GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2000 🢒 S/T Isuzu - 2WD 🢒 DTC 🢒 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 FT values will indicate a change made to the fuel delivery. The ideal fuel trim values are around 128 (0 percent). Whenever the oxygen sensor signal is indicating a lean condition, the PCM will add fuel resulting in fuel trim values above 128 (0 to 100 percent). Whenever a rich condition is detected, the fuel trim values will read below 128 (0 to -100 percent), indicating that the PCM is reducing the amount of fuel delivered. Whenever the exhaust emissions reach an excessive level due to a rich condition, a fuel trim DTC will set.

Conditions for Running the DTC
    • DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0300, P0325, P0335, P0341, P0342, P0446, P0502, P0503, P0506, P0507, P0601, P0602, P1133, and P1441 are not set.
    • The intake air temperature (IAT) is between -25°C (-13°F) and 115°C (175°F).
    • The engine coolant temperature (ECT) is between 60°C (140°F) and 115°C (239°F).
    • Engine speed is between 550 RPM and 3600 RPM.
    • Vehicle speed is below 82 mph.
    • MAP is above 26 kPa.
    • BARO is more than 72 kPa.
    • Fuel ethanol composition less than 88 percent.
    • Fuel level is more than 9.8 percent.

Conditions for Setting the DTC

The fuel trim index is below 65.

Action Taken When the DTC Sets
    • The malfunction indicator lamp (MIL) illuminates if the fault is active within the same conditions for 2 out of 80 ignition cycles.
        OR
    • The MIL will illuminates after two consecutive ignition cycles in which the diagnostic runs with the fault active.
    • The PCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records buffers stores this information.
    • A history DTC is stored.

Conditions for Clearing the MIL/DTC
    • The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault within the Freeze Frame conditions that the DTC failed.
    • A history DTC will clear after 40 consecutive warm up cycles without a fault.
    • A scan tool can 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
    • Check 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. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

    2.

  2. A more negative value indicates the PCM is leaning the fuel mixture (rich condition) and a more positive value indicates the PCM is richening the fuel mixture (lean condition).

    3.

  3. 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 the normal operating temperature.
  3. Monitor the Long Term FT using the scan tool.

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

-18 %

Go to Step 3

Go to Step 4

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 this diagnostic to Run, 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 IAC, if a low or unsteady idle is being experienced.
    • Check for throttle body coking or for objects blocking the IAC passages.
    • Check the O2S 1 electrical connector for contact with the exhaust system.
    • Check the fuel pressure regulator for proper operation. Refer to Fuel System Diagnosis .
    • Check for excessive fuel in the crankcase. Change the 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.

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

380-410

kPa (55-60 psi)

Go to Step 6

Go to Step 12

6

Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test .

Was an injector condition found?

--

Go to Step 10

Go to Step 7

7

Perform the Evaporative Emission Control System Diagnosis .

Was a condition 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.

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

-18 %

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.

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

-18 %

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.

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

-18 %

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 the scan tool in order to clear the DTCs.
  2. Start the engine.
  3. Select DTC and the Specific DTC function.
  4. Enter the DTC number which was set.
  5. Operate the vehicle, within the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

--

Go to Step 14

Go to Step 2

14

Does the scan tool display any additional undiagnosed DTCs?

--

Go to Applicable DTC Table

System OK