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Flexible Fuel (Ff) Sensor

DTC P0176 DETECTION CONDITION AND POSSIBLE CAUSE

DTC P0176 FLEXIBLE FUEL (FF) SENSOR
DETECTION CONDITION 
  • P0176 indicates the FF sensor signal to the PCM fell out of the minimum and maximum calibrated range.
POSSIBLE CAUSE 
  • Open or short in FF sensor VPWR circuit.
  • Open in battery ground to FF sensor circuit.
  • Open in FF sensor signal circuit.
  • Short to ground in FF sensor signal circuit.
  • Fuel contamination.
  • Short to VPWR in FF sensor battery ground circuit.
  • Short to VPWR in FF sensor signal circuit.
  • Fuel separation.
  • Damaged FF sensor.
  • Damaged PCM.
HINT  FF Sensor Description 
  • Capacitive device with a signal processing stage.
  • Determines the percentage of ethanol in the fuel.
    • As the percentage of ethanol in the fuel mixture increases, the output frequency of the sensor will increase.
    • The PCM uses this information to calculate the correct air/fuel ratio and spark advance for the vehicle.
G03988120Courtesy of MAZDA MOTORS CORP.
DTC P0176 INSPECTION

STEP INSPECTION ACTION
1
  • Was PCM Quick Test performed? 
 Yes Go to next step.
No Perform PCM Quick Test.
2 CHECK VPWR VOLTAGE TO FF SENSOR
NOTE: To determine whether the vehicle being serviced is an ethanol application, look at the calibration sticker on the driver side door jamb. A prefix of 610C indicates an ethanol vehicle. Another method is to refer to the fuel filler door; it will read ETHANOL.
  • Disconnect FF sensor.
  • Key ON, Engine OFF (KOEO).
  • Measure voltage between VPWR at the FF sensor harness connector and battery negative post.
  • Key OFF.
  • Was the voltage greater than 10.5 V? 
 Yes Go to next step.
No VPWR circuit fault.
Check condition of fuse 13 in Engine Compartment Fuse/Relay Box. If fuse is damaged, check VPWR circuit for short to ground. If OK, repair open circuit.
Go to step 12.
3 CHECK BATTERY GROUND CIRCUIT FOR OPEN IN HARNESS
  • Measure resistance between BATT GND at the FF sensor harness connector and battery negative post.
  • Is resistance less than 10K ohms? 
 Yes Go to next step.
No Repair open circuit.
Go to step 12.
4 CHECK FF SENSOR SIGNAL CIRCUIT FOR OPEN IN HARNESS
  • Disconnect PCM.
  • Install Breakout Box, leave PCM disconnected.
  • Measure resistance of FF SIG circuit between PCM test pin 34 and the FF sensor harness connector.
  • Is resistance less than 5 ohms? 
 Yes Go to next step.
No Repair open circuit.
Go to step 12.
5 CHECK FF SENSOR SIGNAL CIRCUIT FOR SHORT TO POWER AND SHORT TO GROUND
  • Disconnect NGS Tester.
  • Measure resistance between PCM test pin 34 (FF SIG) and PCM test pin 71 (VPWR).
  • Measure resistance between PCM test pin 34 (FF SIF) and PCM test pin 103.
  • Is each resistance greater than 10K ohms? 
 Yes Go to next step.
No Repair short circuit.
Go to step 12.
6 CHECK FF SENSOR DEDICATED FAILURE MODE PID
  • Reconnect FF sensor.
  • Remove Breakout Box.
  • Reconnect PCM.
  • Key ON, Engine Running (KOER).
  • Access FFFM PID with NGS Tester.
  • Is the FFFM PID indicating an ON condition? 
 Yes Possible FF sensor damage.
Go to next step.
No Key OFF.
For Ethanol Vehicles:
If you know the percentage of ethanol in the fuel of the vehicle, go to step 10.
If you do not know the percentage of ethanol in the fuel, go to step 8.
7 CHECK FF SENSOR FREQUENCY
  • Access the FF PID and record the PID frequency value.
  • Is the FF PID indicating a value within 40-160 Hz? 
 Yes Key OFF.
The FF sensor output does not indicate a failure.
For Ethanol Vehicles:
If you know the percentage of ethanol in the fuel of the vehicle, go to step 10.
If you do not know the percentage of ethanol in the fuel, go to step 8.
No Key OFF.
Go to step 11.
8 DETERMINE SEPARATION POINT OF WATER/ETHANOL AND GASOLINE IN THE FUEL
NOTE: This step requires the use of at least a 25 ml graduated cylinder.
  • Fill graduated cylinder with 4 ml of clean water and then pour water into a clean container.
  • Place the hose end of the fuel drain hose assembly in gas can.
  • Connect fuel drain hose assembly to fuel pressure relief valve. Turn connector clockwise to tighten. Turn ON/OFF valve clockwise to open.
  • Key ON.
  • Allow at least 22 ml of fuel to drain into the gas can.
  • Pour 20 ml of the fuel into the graduated cylinder.
  • Add the 4 ml of water into the graduated cylinder to bring total volume to 24 ml.
  • Insert stopper plug in opening of the graduated cylinder. Hold it in place as you shake cylinder to mix water and fuel. Allow liquid to stand and separate.
    NOTE: After about three minutes, the ethanol and water will mix together and settle to the bottom of the cylinder. The gasoline will rise to the top.
  • Record the level on the graduated cylinder where the ethanol/water mixture and gasoline meet.
  • Have all of the steps been completed? 
 Yes Key OFF.
Reconnect fuel pressure relief valve.
Go to next step.
No Key OFF.
Complete all steps before continuing. Gasoline and water will separate.
9 CALCULATE PERCENTAGE OF ETHANOL IN THE FUEL
  • Use the following equation to calculate and record the percentage of ethanol in the fuel sample collected in step 8: Percent ethanol = (A - 4) x 5
    NOTE: The letter A in the above equation equals the level on the graduated cylinder recorded from step 8 where the ethanol/water mixture and gasoline meet. EXAMPLE: If the reading from step 8 is 14 ml then the percentage of ethanol in the fuel mixture is (14-4) x 5, which equals 50. Therefore, the percentage of ethanol in the fuel mixture is 50. See illustration at the beginning of this test.
  • Has the percentage of ethanol in the fuel mixture been determined? 
 Yes The results are accurate to +/- 10%. Pour any remaining fuel back into the vehicle via the fuel filler.
Go to next step.
No Complete the determination of the ethanol percentage before continuing.
10 CHECK FF SENSOR OPERATION: ETHANOL BLEND FUEL
  • Key ON, Engine Running (KOER).
  • Access the FF PID and record frequency.
  • Using the Flexible Fuel Sensor Ethanol Output chart, determine the corresponding frequency range for the known percentage of ethanol.
  • Is the FF PID value within the frequency range shown on the chart? 
 Yes Key OFF.
Replace the PCM.
Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to step 12.
No Key OFF.
Either the FF sensor is not operating properly or the fuel is contaminated.
Drain the fuel tank and refill with known ethanol blend. Start and run the engine to purge the old fuel from the fuel rails. Repeat step 10. If output frequency still does not match the known ethanol fuel blend, Replace the FF sensor.
Go to step 12.
11 CHECK PCM FUNCTION
  • Disconnect FF sensor.
  • Key ON, Engine OFF (KOEO).
  • Access the FF PID.
  • Using the NGS signal simulator (or equivalent tool), feed a 100 Hz signal into the FF SIG circuit at the FF sensor harness connector.
  • Is the FF PID reflecting the frequency input signal? 
 Yes Key OFF.
Replace FF sensor.
Go to step 12.
No Key OFF.
Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Go to step 12.
12 VERIFY TROUBLESHOOTING OF DTCs COMPLETED
  • Make sure to reconnect all disconnected connectors.
  • Clear DTCs from PCM memory using NGS tester generic OBD-II function.
  • Perform PCM Quick Test.
  • Is same DTC present? 
 Yes Replace PCM. See COMPUTERIZED ENGINE CONTROLS .
Repeat PCM Quick Test.
No If any other DTC is present, go to applicable DTC inspection.
If no DTC is present, troubleshooting complete.
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