Diagnostic Aids

Perform this test only when directed by QUICK TEST. This system test is intended to diagnose the following components and circuits:

• Flex Fuel (FF) sensor.
• Wiring harness circuits (FFS SIG, VPWR and PWR GND).
• Powertrain Control Module (PCM).

1. 1) DTC P0176: Check FF Sensor VPWR Circuit
   
   This DTC indicates failure in the FF sensor and/or circuit. Possible causes for this fault are:
   • Faulty FF sensor.
   • Open or shorted wiring harness circuits.
   • Fuel separation or contamination.
   • Faulty Powertrain Control Module (PCM).

   Turn ignition off. Disconnect FF sensor connector. Turn ignition on. Measure voltage between negative battery terminal and VPWR terminal at FF sensor wiring harness connector. See Fig 1. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair VPWR circuit.

   Fig 1: Identifying Flex Fuel Sensor Circuits & Connector Terminals

   Courtesy of FORD MOTOR CO.
2. 2) Check FF Sensor Ground Circuit Resistance
   
   Turn ignition off. Measure resistance between BATT GND terminal at FF sensor wiring harness connector and negative battery terminal. If resistance is more than 10,000 ohms, repair open circuit. If resistance is 10,000 ohms or less, go to next step.
3. 3) Check FFS SIG Circuit Resistance
   
   Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between FFS SIG terminal of FF sensor wiring harness connector and PCM connector pin No. 34. If resistance is 5 ohms or more, repair open circuit. If resistance is less than 5 ohms, go to next step.
4. 4) Check FFS SIG Circuit Short To Power
   
   Disconnect scan tool Data Link Connector (DLC). Measure resistance between PCM connector pins No. 34 and 71 (VPWR). If resistance is 10,000 ohms or less, repair short circuit. If resistance is more than 10,000 ohms, go to next step.
5. 5) Check FFS SIG Circuit Short To Ground
   
   Measure resistance between PCM connector pin No. 34 and pins No. 51, 77 and 103 (PWR GND). If any resistance reading is 10,000 ohms or less, repair short circuit. If all resistance readings are more than 10,000 ohms, go to next step.
6. 6) Check FF Sensor Dedicated Failure Mode PID
   
   Reconnect all components. Start engine and allow to idle. Connect scan tool to DLC. Using scan tool, select FFFM PID from PID/DATA monitor menu. If PID value indicates ON condition, go to next step and check FF sensor. If PID value does not indicate ON condition, proceed as follows:
   • On ethanol vehicles, if percentage of ethanol in fuel is known, go to step  10).
   • On methanol vehicles, if percentage of methanol in fuel is known, go to step  11).
   • If percentage of ethanol or methanol in fuel is not known, go to next step.
7. 7) Check FF Sensor Frequency
   
   Leave engine idling. Using scan tool, select FF PID from PID/DATA monitor menu. If PID value indicates 40-160 Hz, turn ignition off and go to next step. If PID value does not indicate 40-160 Hz, turn ignition off and go to step  12).
8. 8) Determine Water Ethanol/Methanol & Gasoline Separation Point
   
   Rotunda FFV Fuel Test Kit (014-00770), is required for this test. Turn ignition off. Ensure FF sensor is disconnected. Place hose end of fuel drain hose assembly in clean gas can. Connect fuel drain hose to fuel pressure relief valve. Fill beaker with 5 ml of clean water. Turn connector clockwise to tighten. Turn ON/OFF valve clockwise to open. Turn ignition on and leave on until at least 22 ml of fuel is pumped into gas can. Pour 20 ml of fuel into 25 ml graduated cylinder. Pour 4 ml of water into cylinder. Plug cylinder and shake cylinder. Let cylinder stand for 3 minutes, allowing fluids to separate. Water and methanol (or ethanol and water) will blend and settle on the bottom of cylinder. Gasoline will rise to the top. Record fluid levels and go to next step.
9. 9) Determine Ethanol/Methanol Percentage
   
   To determine the percentage of ethanol/methanol in fuel, perform the following equation:
   • Percent of methanol (or ethanol) = (A - 4) x 5.

   The letter "A" in the above equation equals the level on the graduated cylinder recorded from step 8)  where the methanol/water (or ethanol/water) mixture and gasoline meet. See Fig 2. Example, if reading from step 8)  is 14 ml, then the percentage of methanol (or ethanol) in the fuel mixture is (14 - 4) x 5, which equals 50. Therefore the percentage of methanol (or ethanol) in the fuel mixture is 50 percent.

   The accuracy of this equation is plus or minus 10 percent. Dispose of fuel properly. Go to step  11) for methanol powered vehicles or go to next step for ethanol powered vehicles.

   Fig 2: Testing Flex Fuel Sample

   Courtesy of FORD MOTOR CO.
10. 10) Check FF Sensor (Ethanol Vehicles)
    
    Start engine and allow to idle. Using scan tool, select FF PID from PID/DATA monitor menu. Record frequency reading. Use FF PID to determine blend (percentage) of ethanol. SeeFF PID ETHANOL RATING  table. If FF PID value falls within the frequency range, replace PCM. If FF PID value does not fall within the frequency range, check fuel for contamination. If fuel is not contaminated, replace FF sensor. If fuel is contaminated, drain and refill fuel tank. Start engine and allow to idle until old fuel is purged from fuel rails. Repeat this step. If FF PID value still does not fall within the frequency range, replace FF sensor.
    FF PID ETHANOL RATING ⁽¹⁾
    
    

    Ethanol Blend (FF PID%)	Frequency
    Zero	40-60
    15	50-70
    25	60-80
    35	65-85
    45	75-100
    55	80-105
    65	90-110
    75	95-120
    85	105-125
    (1) Ratings may vary between listed values.

11. 11) Check FF Sensor (Methanol Vehicles)
    
    Start engine and allow to idle. Using scan tool, select FF PID from PID/DATA monitor menu. Record frequency reading. Use FF PID to determine blend (percentage) of methanol. See FF PID METHANOL RATING  table. If FF PID value falls within the frequency range, replace PCM. If FF PID value does not fall within the frequency range, check fuel for contamination. If fuel is not contaminated, replace FF sensor. If fuel is contaminated, drain and refill fuel tank. Start engine and allow to idle until old fuel is purged from fuel rails. Repeat this step. If FF PID value still does not fall within the frequency range, replace FF sensor.
    FF PID METHANOL RATING ⁽¹⁾
    
    

    Methanol Blend (FF PID%)	Frequency
    Zero	40-60
    15	55-75
    25	65-85
    35	75-95
    45	85-105
    55	95-115
    65	105-125
    75	115-135
    85	125-145
    (1) Ratings may vary between listed values.

12. 12) Check PCM Function
    
    Disconnect FF sensor. Using scan tool, select FF PID from PID/DATA monitor menu. Using NGS scan tool signal simulator or equivalent, feed a 100Hz signal into FFS SIG circuit terminal at FF sensor wiring harness connector. Turn ignition on. If FF PID value reflects frequency input signal, replace FF sensor. If FF PID value does not reflect frequency input signal, replace PCM.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 20). No test procedures have been omitted.
13. 20) Continuous DTC P0176
    
    Continuous DTC P0176 indicates failure in the FF sensor and/or circuit. Possible causes for this fault are:
    • Faulty FF sensor.
    • Open or shorted wiring harness circuits.
    • Faulty Powertrain Control Module (PCM).

    Perform KOER ON-DEMAND SELF-TEST . If KOER DTC P0176 is present, hard fault is present. Go to step  1). If KOER DTC P0176 is not present, check for intermittent fault. See TEST Z .