For 1990-2009 cars
Engine Controls Components
Fuel System
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### 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 fuel tank pressure varies. The Fuel Tank Pressure sensor voltage increases as the fuel tank pressure decreases (negative pressure, or vacuum). The Fuel Tank Pressure sensor voltage decreases (positive pressure, low voltage) 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 ignition switch is in the RUN position.

### 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

The EVAP Pressure Sensor monitors a range from 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 water (H2O). Most gauges measure vacuum in inches of mercury (Hg) and pressure in pounds per square inch (psi). The following shows how the values compare:

in H2O | in Hg | psi
--- | --- | ---
1in 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

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step determines if the malfunction is present. If DTC P1635 sets at the same time, this indicates that the 5.0 volt reference circuit is either shorted to ground or shorted to a voltage. The 5 volt reference circuit is internally connected within the PCM. The A/C Refrigerant Pressure sensor may be causing this DTC to set. Refer to DTC P1635 for further diagnosis.

1. 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.

2. This step tests whether the signal circuit is shorted to a voltage.

3. This step tests whether a ground circuit is available for the Fuel Tank Pressure sensor at the body pass through connector.

4. This step tests whether a ground circuit is available for the Fuel Tank Pressure sensor.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn ON the ignition leaving the engine OFF.
2. Monitor the Fuel Tank Pressure sensor voltage using the scan tool.

Is the Fuel Tank Pressure sensor voltage above the specified value?

4.3V

Go to Step 4

Go to Step 3

3 |

1. Turn ON the ignition leaving the engine OFF.
2. Review the Freeze Frame and/or Failure Records data for this DTC and observe the parameters.
3. Turn OFF the ignition for 15 seconds.
4. Idle the engine.
5. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in the Freeze Frame/Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
6. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, then enter the DTC number using the scan tool.

Does the scan tool indicate that this diagnostic failed this ignition?

Go to Step 4

Go to Diagnostic Aids

4 |

1. Disconnect the Fuel Tank Pressure sensor jumper harness at the body pass through connector. Refer to

   #### Outside Left of Rear Floor Pan, Forward of Rear Axle

   (1) | C405B
   (2) | I/P wiring harness
   (3) | C405C
   (4) | Rear wheel speed sensor harness

   in Wiring Systems.
2. Observe the Fuel Tank Pressure sensor voltage displayed on the scan tool.

Is the Fuel Tank Pressure sensor voltage below the specified value?

1.0V

Go to Step 5

Go to Step 11

5 | Probe the sensor ground circuit at the body pass through connector (PCM side) with the test lamp J 35616-200 connected to B+. Is the test lamp illuminated? | -- | Go to Step 6 | Go to Step 12
6 | Measure the voltage at the 5.0 volt reference circuit at the body pass through connector to the battery ground using the DMM J 39200 . Is the voltage near the specified value? | 5.0V | Go to Step 7 | Go to Step 19
7 |

1. Inspect for a poor connections at the body pass through connector. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
2. If you find a poor connection, repair the terminal as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and repair the condition?

--

Go to Step 20

Go to Step 8

8 |

1. Turn OFF the ignition.
2. Re-connect the Fuel Tank Pressure sensor jumper harness to the body pass through connector.
3. Lower the fuel tank to gain access to the Fuel Tank Pressure sensor. Refer to Fuel Tank Replacement .
4. Disconnect the Fuel Tank Pressure Sensor electrical connector.
5. Turn ON the ignition leaving the engine OFF.
6. Observe the Fuel Tank Pressure sensor voltage using a scan tool.

Is the Fuel Tank Pressure sensor voltage below the specified value?

1.0V

Go to Step 9

Go to Step 14

9 | Probe the Fuel Tank Pressure sensor ground circuit with the test lamp J 35616-200 connected to B+ at the Fuel Tank Pressure sensor jumper harness (PCM side). Is the test lamp illuminated? | -- | Go to Step 10 | Go to Step 15
10 | Measure the voltage at the Fuel Tank Pressure sensor 5.0 volt reference circuit to the battery ground using the DMM J 39200 . Refer to Measuring Voltage in Wiring Systems. Is the voltage near the specified value? | 5.0V | Go to Step 17 | Go to Step 16
11 |

1. Test the Fuel Tank Pressure sensor signal circuit for a short to voltage or a short to the 5 volt reference circuit between the body pass through connector and the PCM. Refer to Measuring Voltage in Wiring Systems.
2. Repair the Fuel Tank Pressure sensor signal circuit if the circuit is shorted. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 13

12 |

1. Test for continuity of the Fuel Tank Pressure sensor ground circuit between the body pass through connector and the PCM. Refer to Testing for Continuity in Wiring Systems.
2. Repair the open or the poor connection if the Fuel Tank Pressure sensor ground circuit measures over the specified value. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

2ohms

Go to Step 20

Go to Step 13

13 | Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | Go to Step 20 | --
14 | Repair the poor connection or the signal circuit for a short to voltage in the Fuel Tank Pressure sensor jumper harness. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 20 | --
15 | Repair the poor connection or open ground circuit in the Fuel Tank Pressure sensor jumper harness. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 20 | --
16 | Repair the 5 volt reference circuit in the Fuel Tank Pressure jumper harness for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 20 | --
17 |

1. Inspect for a poor sensor ground terminal connection at the Fuel Tank Pressure sensor jumper harness connector. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
2. If you find a poor connection repair the terminal as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 18

18 | Replace the Fuel Tank Pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | Go to Step 20 | --
19 | Repair the 5 volt reference circuit for a short to voltage between the PCM and the jumper harness. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 20 | --
20 |

1. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool.
2. Idle the engine at the normal operating temperature.
3. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool.
4. 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?

--

Go to Step 21

Go to Step 2

21 | 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 | System OK