P0178
DTC P0178CIRCUIT DESCRIPTION
Alcohol content and fuel temperature information is supplied to the powertrain control module (PCM) from the fuel composition sensor (FCS). The FCS has an ignition 1 circuit, a signal circuit, and a ground circuit. The FCS uses a microprocessor inside the sensor to measure the ethanol percentage and fuel temperature, and changes output signals accordingly. The signal circuit carries both the ethanol percentage, and the fuel temperature within the same signal. The signal is both variable frequency and variable pulse width. The frequency signal indicates the ethanol percentage, and the pulse width indicates fuel temperature. The PCM provides an internal pull up to 5 volts on the signal circuit, and the FCS pulls the 5 volts to ground in pulses. The normal range of operating frequency is between 50-150 Hz. The normal pulse width ranges between 1-5 milliseconds. If the PCM detects a signal less than 45 Hz DTC P0178 will set.
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 below 45 Hz for 12.5 seconds.
DIAGNOSTIC AIDS
- The hertz and millisecond parameters react immediately to any change in the FCS circuits, but may not react long enough to set this DTC.
- A reading of 16 Hz in the Freeze Frame/Failure Records indicates a circuit failure.
- An intermittent condition may not be detected because the sensor does not immediately power down and the connection may be restored before voltage drops below the operating threshold.
- If this DTC will not reset and the parameters are steady, thoroughly inspect all FCS circuits for an intermittent open.
- If a intermittent condition is suspected go to Diagnostic aids for Circuit Testing and wiring Repair Procedures.
TEST
