Refer to Engine Controls Schematics
MIL, Generator, and Fuel Composition Sensor
Circuit Description
Alcohol content information is supplied to the PCM from the fuel composition sensor. The fuel composition sensor measures fuel temperature through an internal thermistor. The fuel conductivity and capacitance are electronically measured inside a small fuel cell. The internal circuitry combines the electrical measurement and fuel temperature information using a microprocessor to produce a Hertz frequency output.
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 below 45 Hz for 12.5 seconds.
Action Taken When the DTC Sets
| • | The 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 it may not occur long enough to set the code. Watch Hz and ms to identify intermittent problems in the signal circuit. An intermittent fault in the signal circuit will immediately change the Hz and ms parameters. The Freeze Frame and Failure Records may be used to reproduce conditions at the time of the failure. A reading of 16 Hz in the Freeze Frame and Failure Records indicates a circuit fault occurred.
The ignition positive voltage circuit needs the fault to occur a longer period of time to affect the sensor output. An intermittent fault here may not show up by looking at Hz or ms because the sensor does not immediately power down and the connection may be restored before voltage drops below the operating threshold (such as a loose terminal). 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.
The J-44175 fuel composition tester can be used to check the accuracy of the sensor if a fault is not isolated using this table. If the Fuel Test is performed before the electrical circuits have been tested using this table, the results will be in error.
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.
-
This step verifies that a fault is present.
-
This step is looking for a reference voltage from the PCM. An excessively high or low voltage is an indication of a problem with the circuit, or a malfunctioning PCM.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | |
Is the FCS reading below the specified value? | 45 Hz | Go to Step 4 | Go to Step 3 | |
3 |
Does the scan tool indicate that DTC P0178 failed this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
4 |
Is the test lamp illuminated? | -- | Go to Step 5 | Go to Step 8 |
5 | With the FCS harness connector still disconnected, connect a test lamp between terminals B and C. Is the test lamp illuminated? | -- | Go to Step 6 | Go to Step 9 |
Is the reading near the specified value? | 5.0 V | Go to Step 12 | Go to Step 7 | |
7 | Check the FCS signal circuit for an open, short to ground or short to voltage. Did you find a condition? | -- | Go to Step 14 | Go to Step 10 |
8 | Repair the open in the FCS ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 14 | -- |
9 | Repair the open in the FCS reference circuit. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 14 | -- |
10 | Inspect the PCM connectors for poor connection and/or terminal contact. Did you find a condition? | -- | Go to Step 14 | Go to Step 11 |
11 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 14 | -- |
12 | Check the FCS connector and PCM terminals for proper terminal contact. Did you find a condition? | -- | Go to Step 14 | Go to Step 13 |
13 | Replace the FCS. Refer to Fuel Composition Sensor Replacement . Is the action complete? | -- | Go to Step 14 | -- |
14 |
Does the scan tool indicate the diagnostic 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 |
