Circuit Description
Alcohol content information is supplied to the powertrain control module (PCM) from the fuel composition sensor. The fuel composition sensor (FCS) measures fuel temperature through an internal thermistor. The fuel conductivity and capacitance are electronically measured inside a small fuel cell. Internal circuitry combines the electrical measurement and fuel temperature information using a microprocessor to produce a Hertz frequency output.
Circuitry inside the sensor provides a default output of 170 Hz if the fuel conductivity is too high or an internal fault is detected. A test of the fuel must be made to determine the cause of the 170 Hz output.
Conditions for Running the DTC
| • | The engine run time is more than 30 seconds. |
| • | The ignition voltage is more than 10.9 volts. |
Conditions for Setting the DTC
The FCS frequency is more than 155 Hz for 12.5 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
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 fault may not occur long enough to set the DTC. Watch Hz and ms to identify intermittent problems in these two circuits.
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. Verify 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.
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This step inspects for a frequency that is out of range or intermittent at the time of the test.
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This step determines if the intermittent high frequency is due to water droplets passing through the sensor.
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This step compares the reading from the FCS 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 |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Is the reading steady, above the specification? | 155 Hz | Go to Step 5 | Go to Step 3 | |
Does the frequency rise above the specification at any time? | 155 Hz | Go to Step 4 | Go to Diagnostic Aids | |
4 |
Is any water present in the sample of fuel taken? | -- | Go to Step 9 | Go to Step 5 |
5 | Connect the flexible fuel line to the injector rail. Perform an accuracy test of the fuel composition tester.
Is the reading within 6 Hz of the specification? | 136 Hz | Go to Step 6 | Go to Step 11 |
|
Important: Drain the acetone completely from the tester. 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.
Is the green LED ON? | -- | Go to Step 8 | Go to Step 7 | |
7 | Is the red LED ON? | -- | Go to Step 9 | Go to Step 11 |
8 |
Is the reading from the scan tool and the DMM within the specified amount? | 12 Hz | Go to Step 9 | Go to Step 10 |
9 | Connect the flexible fuel line to the injector rail.
Did you complete the replacement? | -- | Go to Step 13 | -- |
10 | Replace the FCS. Refer to Fuel Composition Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
11 | Replace the 9-volt battery and refill with a fuel sample. Is the RED or GREEN led ON? | -- | Go to Step 5 | Go to Step 12 |
12 | The fuel composition tester has a malfunction. Send tester to a repair facility. Refer to the user manual for shipping and address information. | -- | -- | -- |
13 |
Does the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 |
14 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
