Circuit Description
The DTC P2027 Fuel Vapor Temperature Sensor Circuit High Voltage diagnostic monitors the fuel vapor temperature sensor signal. A thermistor is a resistor whose value varies with the temperature. The electrical resistance of the vapor temperature sensor is high when the fuel tank vapor temperature is cold, and the resistance is low when the vapor temperature is warm. The sensor is wired in series with a fixed resistor in the powertrain control module (PCM). The PCM applies 5 volts to the vapor temperature sensor. The PCM monitors the voltage across the sensor and converts the voltage into a temperature reading. The voltage measured by the PCM will be high when the vapor temperature is cold, and low when the vapor temperature is warm.
Temperature | Sensor Resistance | Sensor Signal Voltage |
|---|---|---|
Cold | High | High |
Warm | Low | Low |
Condition for Running the DTC
| • | The ignition is ON. |
| • | The intake air temperature at least -14°C (7°F). |
| • | Barometric pressure (BARO) is more than 75 kPa. |
Conditions for Setting the DTC
| • | The fuel vapor temperature signal voltage is more than 4.6 volts. |
| • | The above condition is met for at least 5 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer. |
| • | The PCM enters the Fail-safe mode and assumes that the fuel vapor temperature is fixed at 20°C (68°F). |
Conditions for Clearing the MIL/DTC
| • | The MIL turns off after 3 consecutively passing cycles without a fault present. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool Clear DTC Information function in order to clear the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | A damaged wiring harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the fuel vapor temperature display on the scan tool while moving the connectors and the wiring harnesses related to the fuel vapor temperature sensor. A change in the fuel vapor temperature display will indicate the location of the fault. |
| • | The scan tool displays a default value of 20°C (68°F) when a short to ground or an open circuit is detected. When an open circuit first occurs the scan tool will indicate -40°C (-40°F). After 5 seconds the MIL illuminates, a DTC P2027 sets, and the scan tool now displays the default value of 20°C (68°F). |
| • | When replacing the fuel vapor temperature sensor, the Temperature to Resistance Value scale may be used to test the sensor at various temperature levels to evaluate the possibility of a shifted and incorrectly calibrated sensor. A shifted sensor could result in poor driveability complaints. Refer to Temperature Versus Resistance . |
| • | A short to voltage in the sensor signal circuit may cause DTC P2027 to set. |
An intermittent malfunction may be caused by a fault in the fuel vapor temperature sensor circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .
If the DTC P2027 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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If the FTP sensor reading is near 58.59 mm Hg (31.23 in H2O) there is a fault in the sensor ground circuit or the sensor.
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The scan tool displays a default value of 20°C (68°F) when there is an open circuit or when a short to voltage is present.
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Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P2027 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P2027 appears in the Not Ran Since Code Cleared list, the DTC P2027 diagnostic has not yet run. When the DTC P2027 does not appear in the Not Ran Since Code Cleared list, the DTC P2027 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P2027 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||
Is the sensor near the specified value? | FTP 58.59 mm Hg (31.23 in H2O) | Go to Step 5 | Go to Step 3 | |
Is the fuel vapor temperature at the specified value? | 20°C (68°F) | Go to Step 4 | Go to Diagnostic Aids | |
4 |
Did you find and correct a condition? | -- | Go to Step 11 | Go to Step 6 |
5 |
Did you find and correct a condition? | -- | Go to Step 11 | Go to Step 6 |
6 |
Was the measured resistance near the specified values in the table? | -- | Go to Step 8 | Go to Step 7 |
7 |
Did you find and correct a condition? | -- | Go to Step 11 | Go to Step 9 |
8 |
Did you find and correct a condition? | -- | Go to Step 11 | Go to Step 10 |
9 | Replace the fuel vapor temperature sensor. Refer to Fuel Vapor Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
Does the DTC run and pass? | -- | Go to Step 12 | Go to Step 2 | |
12 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
