GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2000 🢒 S/T Isuzu - 2WD 🢒 DTC 🢒 DTC P0179 Fuel Composition Sensor Circuit High Frequency

Conditions for Running the DTC
    • Engine run time is more than 30 seconds.
    • Ignition voltage is more than 10.9 volts.

Conditions for Setting the DTC

The fuel composition sensor (FCS) frequency is more than 155 Hz for 6.25 seconds.

Action Taken When the DTC Sets
    • The powertrain control module (PCM) illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The PCM turns the MIL OFF after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A last test failed (current DTC) clears when the diagnostic runs and does not fail.
    • A History DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
    • Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

The Hz and ms parameters on the scan tool react immediately to any change of state in the ground or signal circuits. Hz and ms may show a change, but the signal may not occur long enough to set the code. Watch Hz and ms to identify intermittent problems in these two circuits. The Freeze Frame and Failure Records may be used to reproduce conditions at the time of the failure. An Hz reading of 16 in the Freeze Frame and Failure Records indicates a hard fault occurred.

The ignition positive voltage circuit needs a hard fault to set a code. An intermittent fault here may not show up by looking at Hz or ms. If the DTC will not reset and Hz and ms are steady, thoroughly inspect all FCS circuits while paying close attention to the ignition positive voltage circuit wire and or terminals for an intermittent open.

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

The following may cause an intermittent:

    • Mis-routed harness
    • Rubbed through wire insulation
    • Broken wire inside the insulation
    • Poor terminal contact

Test Description

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

  1. This step checks for a frequency that is out of range, or intermittent at the time of the test .

  2. This step determines if the intermittent high frequency is due to water droplets passing through the sensor.

    3.

  3. This step compares the reading from the fuel composition sensor with an external test tool to determine the accuracy of the vehicle sensor and the compatibility of the fuel in the tank

Step

Action

Values

Yes

No

1

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

-

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install a scan tool.
  2. Start the engine and allow the engine to idle.
  3. Read the fuel composition frequency on the scan tool.

Is the reading steady, above the specification?

155 Hz

Go to Step 5

Go to Step 3

3
  1. Allow the engine to idle.
  2. Agitate the fuel in the fuel tank by pushing the rear of the vehicle from side to side for 5 seconds.
  3. Monitor the scan tool fuel composition frequency for 5 minutes.

Does the frequency rise above the specification at any time?

155 Hz

Go to Step 4

Go to Diagnostic Aids

4
  1. Turn the engine OFF.
  2. Relieve the fuel system pressure. Refer to Fuel Pressure Relief .
  3. Remove the flexible fuel line from the injector fuel rail.
  4. Place the flexible fuel line into a suitable container and activate the fuel pump. Collect about 1 liter of fuel and allow the fuel sample to settle.

Is any water present in the sample of fuel taken?

--

Go to Step 9

Go to Step 5

5

Important: Clean the beaker with a clean dry paper towel before taking a fuel sample. Be careful not to allow fingerprints, sweat, water or any other outside debris contaminate the fuel sample, beaker, tester or fuel gauge as this will cause an error in the test result, leading to a misdiagnosis.

  1. Perform a fuel test using the J-44175 fuel composition tester.
  2. Install a fuel pressure gauge into the service port located on the rear of the injector rail.
  3. Start the engine and open the valve on the fuel pressure gauge. Allow enough fuel to pass through the gauge to flush any previous fuel from inside the hose.
  4. Draw fuel from the fuel pressure gauge into the beaker supplied with the test kit.
  5. Transfer the fuel from the beaker into the fuel tester.
  6. Turn ON the fuel tester and note the red and green LED.

Is the green LED ON?

--

Go to Step 7

Go to Step 6

6

Is the red LED ON?

--

Go to Step 10

Go to Step 13

7
  1. Connect a DMM to the fuel tester terminals.
  2. Set the DMM to the AC Hz scale and take a reading of the fuel sample.
  3. Start the engine and monitor the fuel composition frequency on the scan tool.

Is the readings from the scan tool and the DMM within the specified amount?

11 Hz

Go to Step 10

Go to Step 8

8
  1. Drain the sample fuel from the fuel tester.
  2. Allow any residual fuel in the tester to evaporate.
  3. Fill the fuel composition tester with (acetone) and take a reading with the DMM set to AC Hz scale.

Is the reading within 10 Hz of the specification?

50 Hz

Go to Step 11

Go to Step 13

9
  1. Connect the flexible fuel line to the injector rail if it was previously removed.
  2. Disconnect the fuel composition sensor electrical harness.
  3. Install 3 jumper wires between the fuel composition sensor and the electrical connector harness.
  4. Connect a DMM set to AC Hz scale, to the fuel composition sensor ground and signal circuit jumpers.
  5. Start the engine and monitor the fuel composition frequency on the scan tool and the Hz reading on the DVM.

Is the DVM and the scan tool reading within the specification?

11 Hz

Go to Step 11

Go to Step 10

10
  1. The fuel is contaminated.
  2. Drain the fuel tank.
  3. Replace the fuel with E85 or less.

Is the action complete?

--

Go to Step14

--

11

Replace the fuel composition sensor.

Is the action complete?

--

Go to Step 14

--

12

Important: The PCM must be reprogrammed.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 14

--

13

Replace the 9 volt battery and retest. If the result is the same, the tester will need to be sent out for repair.

--

--

--

14
  1. Select DTC and Clear DTC information function with a scan tool.
  2. Start the engine.
  3. Allow the engine to idle until the engine reaches normal operating temperature.
  4. Select DTC and Specific DTC function.
  5. Enter the DTC number that was set.
  6. Operate the vehicle within the Conditions for Setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic Ran and Passed?

-

Go to Step 15

Go to Step 2

15

Does the scan tool display any additional undiagnosed DTCs?

-

Go to applicable DTC table

System OK