On Board Diagnostics II PCED

1999 PCED On Board Diagnostics II

SECTION 5: Pinpoint Tests

DE: Flexible Fuel (FF) Sensor

DE1 DTC P0176: CHECK VPWR VOLTAGE TO FF SENSOR

Note: To determine whether the vehicle being serviced is an ethanol or methanol application, look at the calibration sticker on the door jamb. A prefix of 610 C indicates an ethanol vehicle. A prefix of 610 G indicates a methanol vehicle. Another method is to refer to the fuel filler door; it will read either METHANOL or ETHANOL.

Disconnect FF sensor.
Key on.
Measure VPWR circuit voltage between the VPWR circuit at the FF sensor harness connector and battery negative post.

Is the voltage greater than 10.5 volts?

Yes	No
KEY OFF. GO to DE2 .	VPWR circuit fault. KEY OFF. CHECK condition of related fuses/fuse links. If OK, REPAIR open circuit. If fuse/fuse link is damaged, CHECK VPWR circuit for short to ground. REPAIR as necessary.

DE2 CHECK BATTERY GROUND CIRCUIT FOR OPEN IN HARNESS

Measure resistance between battery ground circuit at the FF sensor harness connector and battery negative post.

Is resistance less than 10,000 ohms?

Yes	No
GO to DE3 .	REPAIR open circuit.

DE3 CHECK FF SENSOR SIGNAL CIRCUIT FOR OPEN IN HARNESS

Measure resistance between PCM harness connector pin 34 and FF sensor signal circuit at the FF sensor harness connector.

Is resistance less than 5 ohms?

Yes	No
GO to DE4 .	REPAIR open circuit.

DE4 CHECK FF SENSOR SIGNAL CIRCUIT FOR SHORT TO POWER

Disconnect scan tool.
Disconnect PCM.
Measure resistance between PCM harness connector pin 34 and pin 71.

Is resistance greater than 10,000 ohms?

Yes	No
GO to DE5 .	REPAIR short circuit.

DE5 CHECK FF SENSOR SIGNAL CIRCUIT FOR SHORT TO GROUND

Measure resistance between PCM harness connector pin 34 and pins 51, 77 and 103.

Is each resistance greater than 10,000 ohms?

Yes	No
GO to DE6 .	REPAIR short circuit.

DE6 CHECK FF SENSOR DEDICATED FAILURE MODE PID

Flex fuel sensor connected.
Connect scan tool.
Connect PCM.
Key on, engine running.

Is the FFFM PID indicating an ON condition?

Yes	No
Possible FF sensor damage. GO to DE7 .	KEY OFF. For Ethanol Vehicles: If you know the percentage of ethanol in the fuel of the vehicle, GO to DE10 . For Methanol Vehicles: If you know the percentage of methanol in the fuel of the vehicle, GO to DE11 . If you do not know the percentage of ethanol or methanol in the fuel, GO to DE8 .

DE7 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	No
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 DE10 . For Methanol Vehicles: If you know the percentage of methanol in the fuel of the vehicle, GO to DE11 . If you do not know the percentage of ethanol or methanol in the fuel, GO to DE8 .	KEY OFF. GO to DE12 .

DE8 DETERMINE SEPARATION POINT OF WATER/METHANOL (OR WATER/ETHANOL) AND GASOLINE IN THE FUEL

Note: This step requires the Rotunda Fuel Composition Test Kit 014-00770 or equivalent.

Fill beaker with 5 ml of clean water.
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 22 ml of fuel to drain into the gas can.
Pour 20 ml of the fuel into 25 ml graduated cylinder.
Pour enough water from the beaker into the 25 ml graduated cylinder to bring total volume to 24 ml.
Insert stopper plug in opening of 25 ml 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 methanol and water (or 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 methanol/water (or ethanol/water) mixture and gasoline meet.

Have all of the steps been completed?

Yes	No
KEY OFF. RECONNECT fuel pressure relief valve. GO to DE9 .	KEY OFF. COMPLETE all steps before continuing. Gasoline and water will separate. However, if the fuel does not appear to separate, then the fuel is either 100% methanol or a mixture of methanol and water.

DE9 CALCULATE PERCENTAGE OF METHANOL (OR ETHANOL) IN THE FUEL

Use the following equation to calculate and record the percentage of methanol (or ethanol) in the fuel sample collected in step DE8 :

Percent methanol (or ethanol) = (A - 4) x 5

Note: The letter A in the above equation equals the level on the graduated cylinder recorded from step DE8 where the methanol/water (or ethanol/water) mixture and gasoline meet; see illustration below.

EXAMPLE: If the reading from step DE8 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.

Has the percentage of methanol (or ethanol) in the fuel mixture been determined?

Yes	No
The results are accurate to +/- 10%. POUR any remaining fuel back into the vehicle via the fuel filler. For ethanol vehicles: GO to DE10 . For methanol vehicles: GO to DE11 .	COMPLETE the determination of the methanol (or ethanol) percentage before continuing.

DE10 CHECK FF SENSOR OPERATION: ETHANOL BLEND FUEL

Key on, engine running.
Access the FF PID and record frequency.
Using chart below, 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	No
KEY OFF. REPLACE the PCM.	KEY OFF. Either the FF sensor is not operating properly or the fuel is contaminated. LOWER and DRAIN the fuel tank and refill with known ethanol blend. START and RUN engine to purge the old fuel from the fuel rails, then REPEAT step DE10 . If output frequency still does not match the known ethanol fuel blend, REPLACE the FF sensor.

DE11 CHECK FF SENSOR OPERATION: METHANOL FUEL BLEND

Key on, engine running.
Access the FF PID and record frequency.
Using the chart below, determine the corresponding frequency range for the known percentage of methanol.

Is the FF PID value within the frequency range shown on the chart?

Yes	No
KEY OFF. REPLACE the PCM.	KEY OFF. Either the FF sensor is not operating properly or the fuel is contaminated. LOWER and DRAIN the fuel tank and refill with known methanol blend. START and RUN engine to purge the old fuel from the fuel rails, then REPEAT step DE11 . If output frequency still does not match the known methanol fuel blend, REPLACE the FF sensor.

DE12 CHECK PCM FUNCTION

Disconnect FF sensor.
Connect scan tool.
Access the FF PID.
Using the NGS signal simulator, or equivalent tool, feed a 100 Hz signal into the FFS signal circuit at the FF sensor harness connector.
Key on.

Is the FF PID reflecting the frequency input signal?

Yes	No
KEY OFF. REPLACE FF sensor.	KEY OFF. REPLACE PCM (refer to Section 2 , Flash EEPROM).

DE20 DTC P0176: COMPLETE KOER SELF-TEST

Output all KOER self-test DTCs.

Note: Ignore all other DTCs output at this time.

Is P0176 output in KOER?

Yes	No
KEY OFF. GO to DE1 and ADDRESS the KOER DTC.	KEY OFF. The FF sensor circuit fault is intermittent. GO to Pinpoint Test Step Z1 .