Circuit Description
The PCM uses the 5 Volt Reference B circuit to feed the fuel tank pressure sensor.
The PCM monitors the voltage on the 5 Volt Reference B circuit. If the voltage is outside an acceptable range, DTC P1639 will set.
Conditions for Running the DTC
The ignition switch is ON.
Conditions for Setting the DTC
| • | The PCM detects a voltage out of range condition on the 5 Volt Reference B circuit. |
| • | The condition exists for less than 1 second. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test runs and fails. |
| • | The PCM stores the conditions present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF after the third consecutive trip in which the diagnostic runs and passes. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
If the condition is intermittent, refer to Intermittent Conditions in Symptoms.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if the fuel pump control circuit is causing the condition.
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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.
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This step determines the location of the condition. If the scan tool displays 5 volt reference B OK, then the fault is isolated to the fuel tank pressure sensor, or jumper harness.
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This step determines if the 5 volt reference circuit is shorted to a ground.
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If the DMM displays 5 volts, inspect the fuel tank jumper harness for signs of damage.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | ||
Does the scan tool display 5 volt reference B fault? | -- | |||
Does the 5 volt reference B display fault when the fuel pump is enabled? | -- | |||
Does the scan tool indicate that this diagnostic failed this ignition? | -- | Go to Intermittent Conditions | ||
Does the scan tool display 5 volt reference B as fault? | -- | |||
Probe the fuel tank pressure sensor 5 volt reference circuit at connector C415 with a test lamp connected to B+. Does the test lamp illuminate? | -- | |||
Is the voltage near the specified value? | 5V | |||
8 | Test the fuel tank pressure sensor 5 volt reference circuit for a short to ground between connector C415 and the PCM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
9 | Test the fuel tank pressure sensor 5 volt reference circuit for a short to voltage between connector C415 and the PCM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
10 | Inspect the fuel tank pressure sensor jumper harness for damage. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
11 | Repair the 5 volt reference circuit for a short to voltage, or short to ground, between the sensor harness connector and connector C415. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
12 | Repair the fuel tank pressure sensor 5 volt reference circuit for a short to the fuel pump control circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
13 | Replace the Fuel Tank Pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | -- | |
14 |
Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | |
15 | Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, if applicable. Does the scan tool indicate that this test ran and passed? | -- | ||
16 | Select the Capture Info option and the Review Info option with the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |
