Circuit Description
The Fuel Tank Pressure sensor changes resistance based on the fuel tank pressure (or vacuum). A vacuum is considered negative pressure.
The PCM provides a 5.0 volt reference and a ground. The Fuel Tank Pressure sensor signal varies between ground and 5.0 volts as the fuel tank pressure varies. The Fuel Tank Pressure sensor voltage increases as the fuel tank pressure decreases. The Fuel Tank Pressure sensor voltage decreases as the fuel tank pressure increases. The PCM uses the Fuel Tank Pressure sensor voltage for EVAP system leak detection. This DTC sets when the Fuel Tank Pressure sensor signal goes above a predetermined value.
Conditions for Setting the DTC
The engine is operating.
Conditions for Setting the DTC
| • | The Fuel Tank Pressure sensor voltage is greater than 4.90 volts. |
| • | All conditions present for greater than 5.0 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 OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
Diagnostic Aids
Important:
• Remove any debris from the PCM\TAC module connector surfaces before
servicing the PCM\TAC module. Inspect the PCM\TAC module connector gaskets
when diagnosing/replacing the modules. Ensure that the gaskets are installed
correctly. The gaskets prevent contaminate intrusion into the PCM\TAC
modules. • For any test that requires probing the PCM or a component
harness connector, use the Connector Test Adapter Kit J 35616
. Using this kit prevents damage
to the harness/component terminals. Refer to
Using Connector Test Adapters
in Wiring Systems.
| • | The following may cause an intermittent: |
| - | Poor connections; Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems. |
| - | Mis-routed harness. |
| - | Rubbed through wire insulation. |
| - | Broken wire inside the insulation. |
| • | The EVAP Pressure Sensor range is 7.5 in. H2O of pressure to -17.5 in. H2O of pressure (vacuum). |
| • | The vacuum and pressure in the EVAP system is measured in inches of H2O (water). Most gauges measure vacuum in inches of Hg (mercury) and pressure in psi (pounds per square inch). The following shows how the values compare: |
in. H2O | in. Hg. | psi |
|---|---|---|
1 in. H2O | 0.07 in. Hg | 0.0361 psi. |
5 in. H2O | 0.36 in. Hg | 0.180 psi. |
10 in. H2O | 0.73 in. Hg | 0.361 psi. |
15 in. H2O | 1.10 in. Hg | 0.541 psi. |
| • | Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This isolates when the DTC failed. |
| • | For an intermittent, refer to Symptoms . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if the malfunction is present.
-
Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616 . Using this kit prevents any damage to the harness connector terminals.
-
This step checks whether the signal circuit is shorted to a voltage.
-
This step checks whether a ground circuit is available at the Fuel Tank Pressure sensor. For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616 . Using this kit will prevent any damage to the harness connector terminals.
-
Remove the Fuel Tank Pressure sensor vacuum hose and check if vacuum is available to the sensor. Also, inspect the vacuum hose for being disconnected, and for nicks and cuts.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Did DTC P1639 fail this ignition cycle? | -- | |||
Monitor the Fuel Tank Pressure sensor voltage on the Engine 1 Data List on the scan tool. Is the Fuel Tank Pressure sensor voltage above the specified value? | 4.3V | |||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Diagnostic Aids | ||
Is the Fuel Tank Pressure sensor voltage below the specified value? | 1V | |||
Probe the Fuel Tank Pressure sensor ground circuit with a test lamp J 35616-200 connected to B+. Is the test lamp illuminated? | -- | |||
7 |
Is the Fuel Tank Pressure sensor signal circuit shorted? | -- | ||
8 | Measure the voltage at the 5 volt reference circuit to the battery ground using a DMM J 39200 . Is the voltage near the specified value? | 5V | ||
Check for a plugged or leaking vacuum supply to the Fuel Tank Pressure sensor. Is the vacuum supply OK? | -- | |||
10 |
Did the terminal require replacement? | -- | ||
11 |
Did you find and correct the condition? | 5ohms | ||
12 |
Important: Program the replacement PCM. Refer to Powertrain Control Module/Throttle Actuator Control Module Replacement . Replace the PCM. Is the action complete? | -- | -- | |
13 | Replace the Fuel Tank Pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | -- | |
14 | Repair the faulty vacuum supply. Is the action complete? | -- | -- | |
15 | Repair the 5 volt reference circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
16 |
Does the scan tool indicate that this test ran and passed? | -- | ||
17 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
