P2027 Evaporative Emissions (EVAP) Fuel Vapor Temperature Sensor Circuit High Voltage

P2027 Evaporative Emissions (EVAP) Fuel Vapor Temperature Sensor Circuit High Voltage is a generic OBD-II diagnostic trouble code indicating that the vehicle's control module has detected a higher-than-expected voltage signal in the EVAP fuel vapor temperature sensor circuit.

The EVAP system is designed to control fuel vapors produced inside the fuel tank and fuel system so that they are not released directly into the atmosphere. The fuel vapor temperature sensor provides the engine or emissions control module with information about the temperature of fuel vapor within the EVAP system.

In simple terms, P2027 means that the ECM or PCM is seeing an abnormally high electrical voltage from the EVAP fuel vapor temperature sensor circuit.

The phrase "High Voltage" does not necessarily mean that the fuel vapor itself is too hot.

Instead, the problem is generally related to the electrical signal reaching the control module.

Possible causes include:

• Faulty EVAP fuel vapor temperature sensor

• Open sensor circuit

• Broken signal wire

• Disconnected sensor

• Loose connector

• Corroded terminals

• Poor terminal contact

• Short to voltage

• Damaged wiring

• Missing sensor ground

• Incorrect reference voltage

• Moisture intrusion

• Wiring chafing

• Heat-damaged harness

• Incorrect sensor installation

• Faulty control module

• Software or calibration problems

One particularly important possibility is an open circuit. On many temperature-sensor systems, an open circuit can allow the signal voltage to rise toward the reference voltage, causing the control module to interpret the condition as a high-voltage fault.

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What Does P2027 Mean?

The code description contains several important terms.

Evaporative Emissions (EVAP)

EVAP stands for Evaporative Emission Control System.

Its purpose is to prevent gasoline vapors from escaping into the atmosphere.

Gasoline naturally produces vapor, particularly as fuel temperature and ambient temperature change.

The EVAP system captures these vapors and allows them to be managed by the engine under appropriate operating conditions.

A typical EVAP system may include:

• Fuel tank

• Fuel filler neck

• Fuel cap or capless filler system

• Charcoal canister

• Purge valve

• Vent valve

• EVAP hoses

• Pressure sensor

• Temperature sensor

• Leak-detection components

The exact configuration varies by manufacturer and vehicle.

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Fuel Vapor Temperature Sensor

The fuel vapor temperature sensor measures temperature conditions associated with fuel vapor in the EVAP system.

Depending on the vehicle, it may be:

• A separate temperature sensor

• Integrated into the EVAP system

• Integrated into a vapor or pressure-sensing assembly

The sensor sends an electrical signal to the control module.

The module uses this information together with other EVAP parameters to evaluate system operation.

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Circuit High Voltage

This is the most important part of P2027.

A high-voltage circuit code does not necessarily mean excessive fuel vapor temperature.

It means the electrical signal monitored by the control module is higher than the value it expects.

For example, the control module may normally see a variable voltage from the sensor.

If the signal rises close to the circuit's reference voltage because of an open circuit or another electrical problem, the module may identify the condition as:

EVAP fuel vapor temperature sensor circuit high voltage

Therefore, the first diagnostic step should be to determine whether the high voltage is being caused by:

1. A defective sensor

2. An open circuit

3. A short to voltage

4. A wiring problem

5. A connector problem

6. A reference-voltage problem

7. A control-module problem

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How Does the EVAP Fuel Vapor Temperature Sensor Work?

Many automotive temperature sensors use a thermistor.

A common design is an NTC thermistor, where electrical resistance decreases as temperature increases.

The control module monitors the sensor circuit and uses the electrical characteristics of the sensor to calculate temperature.

The simplified process is:

Fuel vapor temperature changes → Sensor resistance changes → Circuit voltage changes → ECM calculates temperature

If the circuit becomes open, the expected electrical relationship changes.

Depending on the circuit design, the signal can rise toward the reference voltage.

This can result in a high-voltage diagnostic code.

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Why Can an Open Circuit Cause P2027?

An open circuit is one of the most important possibilities to understand.

Consider a simplified temperature-sensor circuit:

Reference voltage → Sensor → Ground

The sensor's resistance influences the voltage monitored by the control module.

If the sensor is disconnected or the signal wire breaks:

Sensor disconnected → Electrical circuit becomes open → Signal voltage rises → ECM detects high voltage → P2027

This means P2027 can sometimes be caused by a relatively simple problem such as:

• Unplugged connector

• Broken wire

• Failed splice

• Loose terminal

• Damaged sensor

The sensor itself may not necessarily be defective.

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Symptoms of P2027

P2027 often causes limited driving symptoms because the EVAP system is primarily an emissions-control system.

Check Engine Light

The most common symptom is an illuminated Check Engine Light.

The light may appear after the control module detects the high-voltage condition during one or more diagnostic cycles.

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EVAP or Emissions Warning

Some vehicles may display an emissions-related warning message.

The exact warning depends on the manufacturer.

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Increased Evaporative Emissions

If the EVAP system cannot properly monitor vapor temperature, emissions-control performance may be affected.

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Gasoline Smell

A gasoline smell may sometimes accompany an EVAP problem.

However, P2027 by itself does not prove that there is a fuel leak.

If gasoline smell is present, the fuel system and EVAP system should be inspected for physical leaks.

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Difficult Refueling

Some vehicles with EVAP problems may experience:

• Fuel nozzle repeatedly clicking off

• Slow fuel filling

• Difficulty refueling

These symptoms are more commonly associated with EVAP ventilation restrictions and are not specific to P2027.

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Slight Fuel-Economy Changes

Fuel economy may change in some circumstances, but P2027 alone does not necessarily cause a noticeable fuel-consumption problem.

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Normal Engine Performance

Many vehicles with P2027 will continue to:

• Start normally

• Idle normally

• Accelerate normally

• Drive normally

The Check Engine Light may be the only obvious symptom.

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Common Causes of P2027

Faulty EVAP Fuel Vapor Temperature Sensor

The sensor may have an internal electrical failure.

Possible failures include:

• Internal open circuit

• Incorrect resistance

• Internal connection failure

• Sensor degradation

• Implausible temperature output

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Open Sensor Circuit

An open circuit is a major possibility with a high-voltage fault.

Possible causes include:

• Broken signal wire

• Disconnected sensor

• Damaged connector

• Broken terminal

• Failed splice

• Severed wiring

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Broken Signal Wire

A signal wire can break inside its insulation.

The outside of the wire may appear normal while the conductor inside is electrically open.

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Disconnected Sensor Connector

A connector that has become unplugged can leave the sensor circuit open and cause the signal voltage to rise.

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Corroded Connector Terminals

Corrosion can interfere with the electrical connection.

Possible results include:

• Increased resistance

• Signal instability

• Intermittent connection

• Open-circuit behavior

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Poor Terminal Tension

A terminal can look clean while failing to maintain sufficient contact with the sensor pin.

Vibration can then cause the circuit to open temporarily or completely.

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Short to Voltage

If the sensor signal wire contacts a powered circuit, the control module may see a voltage higher than expected.

Possible causes include:

• Damaged insulation

• Harness chafing

• Incorrect previous repair

• Wiring routed incorrectly

• Melted wiring

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Missing Sensor Ground

Depending on the circuit design, a poor or missing sensor ground can cause an abnormal signal.

Possible causes include:

• Broken ground wire

• Corroded ground point

• Loose ground connection

• Damaged ground splice

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Incorrect Reference Voltage

If the sensor receives an incorrect reference voltage, the resulting signal may exceed the expected range.

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Moisture Intrusion

EVAP components and wiring may be exposed to:

• Rain

• Road spray

• Mud

• Snow

• Road salt

Moisture inside a connector can cause corrosion and electrical faults.

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Wiring Chafing

EVAP wiring may rub against:

• Fuel tank brackets

• Body panels

• Suspension components

• Exhaust components

• Metal edges

Over time, the insulation can wear away and create electrical faults.

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Heat-Damaged Wiring

If the harness is routed near exhaust components, excessive heat can damage the insulation and electrical conductors.

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Incorrect Sensor Installation

An incorrectly installed or incorrect replacement sensor may produce an electrical signal that does not match the control module's expected characteristics.

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Faulty Control Module

In rare cases, the control module may have an internal input-circuit problem.

The module should generally be considered only after the sensor, wiring, connector, supply, and ground have been tested.

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Software or Calibration Problem

A software or calibration problem may cause incorrect monitoring of the EVAP temperature-sensor circuit.

A manufacturer software update may be available for some vehicles.

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Vehicles Commonly Affected by P2027

P2027 can occur on vehicles equipped with an EVAP fuel vapor temperature sensor and the corresponding emissions-monitoring strategy.

Examples may include:

• Ford Mustang

• Ford F-150

• Ford Explorer

• Chevrolet Silverado

• Chevrolet Tahoe

• Chevrolet Suburban

• GMC Sierra

• GMC Yukon

• Cadillac Escalade

• Dodge Charger

• Dodge Challenger

• Jeep Grand Cherokee

• Ram 1500

• Toyota Tundra

• Toyota Sequoia

• Toyota Tacoma

• Nissan Altima

• Nissan Pathfinder

• Nissan Armada

• BMW 3 Series

• BMW 5 Series

• Mercedes-Benz C-Class

• Mercedes-Benz E-Class

• Volkswagen Passat

• Audi A4

This list is not exhaustive.

The exact application of P2027 depends on the vehicle's EVAP system, engine, model year, sensor design, and control-module configuration.

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How Is P2027 Diagnosed?

The main diagnostic question is:

Is the EVAP fuel vapor temperature actually high, or is the sensor circuit producing an abnormally high electrical voltage?

The circuit should be tested before assuming that the fuel vapor temperature is excessive.

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Step 1: Scan for Additional Trouble Codes

Use a suitable diagnostic scan tool to retrieve all stored and pending codes.

Look for faults involving:

• EVAP temperature sensor

• EVAP pressure sensor

• Purge valve

• Vent valve

• Fuel tank pressure

• EVAP leaks

• Wiring

• Communication

Additional codes can help identify the root cause.

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Step 2: Review Freeze-Frame Data

Review the operating conditions under which P2027 was stored.

Check available information such as:

• Engine temperature

• Ambient temperature

• Fuel level

• Vehicle speed

• Engine load

• EVAP temperature

• EVAP pressure

• Battery voltage

If the vehicle has been sitting for hours but the EVAP temperature sensor reports an extremely high temperature, an electrical problem becomes more likely.

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Step 3: Monitor Live Sensor Data

Use a scan tool to monitor the EVAP fuel vapor temperature sensor.

Look for:

• Extremely high temperature readings

• Frozen readings

• Implausible readings

• Sudden changes

• Readings inconsistent with actual conditions

A high temperature reading on a cold vehicle can be an important clue.

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Step 4: Inspect the Sensor

Inspect the sensor for:

• Physical damage

• Corrosion

• Contamination

• Incorrect installation

• Damaged terminals

• Loose connection

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Step 5: Inspect the Connector

Check for:

• Disconnected terminals

• Corrosion

• Moisture

• Bent pins

• Loose pins

• Poor terminal tension

• Damaged seals

• Broken locking mechanism

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Step 6: Check for an Open Circuit

Test the applicable sensor circuit for continuity according to the manufacturer's procedure.

Check:

• Signal wire

• Ground

• Reference or supply circuit

• Harness connections

• Splices

An open signal circuit is a major possibility with P2027.

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Step 7: Check Sensor Reference or Supply Voltage

Measure the applicable voltage at the sensor.

Compare the measurement with the manufacturer's specification.

Do not assume that every EVAP temperature sensor uses the same electrical configuration.

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Step 8: Check Sensor Ground

Verify that the sensor has a proper ground where required.

A poor ground can cause incorrect sensor signals.

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Step 9: Check for a Short to Voltage

Test the signal circuit for unwanted contact with:

• Battery voltage

• Ignition voltage

• Another powered circuit

A short to voltage can directly cause a high-voltage signal.

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Step 10: Check for a Short to Ground

Although a short to ground generally produces a lower signal, it should still be checked when diagnosing the complete circuit.

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Step 11: Check Sensor Resistance

If the sensor is a thermistor, measure its resistance.

Compare the measured value with the manufacturer's specification at the actual sensor temperature.

An internally open sensor may show:

• Very high resistance

• Infinite resistance

• Unstable resistance

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Step 12: Compare Sensor Reading With Actual Temperature

Compare the scan-tool temperature reading with the actual environmental and vehicle conditions.

For example, if the vehicle has been parked overnight and the EVAP temperature sensor reports an extreme temperature, the sensor or circuit may be faulty.

The sensor does not necessarily need to match ambient temperature exactly because it measures a different location.

The purpose is to identify clearly implausible readings.

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Step 13: Perform a Wiggle Test

Monitor the sensor signal while carefully moving the wiring and connector.

If the voltage changes when the harness is moved, an intermittent wiring or connector problem may exist.

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Step 14: Inspect the EVAP Harness

Follow the wiring around:

• Fuel tank

• EVAP canister

• EVAP valves

• Underbody areas

• Exhaust components

Look for:

• Chafing

• Broken wires

• Heat damage

• Crushed wiring

• Loose clips

• Previous repairs

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Step 15: Inspect Other EVAP Components

If additional EVAP codes are present, inspect:

• Charcoal canister

• Purge valve

• Vent valve

• EVAP hoses

• Fuel tank connections

• Pressure sensor

• Leak-detection components

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Step 16: Check for Physical EVAP Leaks

If other EVAP leak codes are present, perform the appropriate leak test.

A smoke test may be used where appropriate.

However, a physical EVAP leak does not automatically explain a high-voltage sensor-circuit code.

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Step 17: Check Fuel Level

Fuel level can influence EVAP operating conditions and diagnostic testing.

Verify the fuel level and compare it with the manufacturer's test requirements.

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Step 18: Check the Control Module Input

If the sensor and wiring are confirmed to be correct, verify that the control module is correctly receiving and interpreting the signal.

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Step 19: Check Manufacturer Technical Information

Look for:

• Technical Service Bulletins

• Known sensor failures

• Wiring harness issues

• Connector problems

• Sensor revisions

• Software updates

• EVAP diagnostic procedures

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Step 20: Perform a Complete EVAP Verification

After repairs, verify:

• Fuel vapor temperature signal

• Sensor circuit voltage

• Sensor resistance where applicable

• EVAP pressure

• Purge operation

• Vent operation

• EVAP leak status

• EVAP diagnostic monitor status

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How to Fix P2027

The correct repair depends on the actual reason for the high voltage.

Replace the Fuel Vapor Temperature Sensor

If testing confirms that the sensor itself is defective, replace it with the correct vehicle-specific component.

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Repair an Open Circuit

If the sensor circuit is open, repair or replace the damaged wiring.

Possible repairs include:

• Repairing broken conductors

• Repairing damaged splices

• Replacing damaged wiring

• Restoring connector terminals

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Repair the Sensor Connector

If the connector has:

• Corrosion

• Moisture damage

• Loose terminals

• Bent pins

• Damaged seals

• Poor terminal tension

repair or replace it as necessary.

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Repair a Short to Voltage

If the signal wire is contacting battery voltage or another powered circuit, locate and repair the damaged wiring.

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Repair Sensor Ground Problems

Repair:

• Broken ground wires

• Corroded grounds

• Loose ground connections

• Damaged ground splices

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Correct Reference Voltage Problems

If the reference or supply voltage is outside specification, diagnose and repair the applicable electrical circuit.

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Repair EVAP Harness Damage

Repair harness damage caused by:

• Chafing

• Heat

• Vibration

• Moisture

• Road debris

• Previous repairs

Secure the harness correctly after repair.

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Repair Related EVAP Problems

If additional EVAP faults are discovered, repair the affected components.

These may include:

• Purge valve

• Vent valve

• Charcoal canister

• EVAP hoses

• Fuel tank connections

• Pressure sensor

• Leak-detection components

Do not replace unrelated EVAP components solely because P2027 is stored.

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Repair or Replace the Control Module

If the sensor and complete circuit are confirmed to be correct but the control module continues to report an incorrect high voltage, the module may require further testing, programming, repair, or replacement.

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Update Control Module Software

If the manufacturer has released a software update addressing P2027 or EVAP temperature-sensor monitoring, apply the appropriate update.

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Clear the Code and Verify the Repair

After completing the repair:

1. Clear P2027.

2. Monitor the EVAP fuel vapor temperature data.

3. Verify that the sensor signal is within the expected range.

4. Check sensor supply and ground.

5. Verify the circuit for an open condition.

6. Check for shorts to voltage.

7. Perform a wiggle test where appropriate.

8. Operate the EVAP system under the required conditions.

9. Complete the appropriate drive cycle.

10. Confirm that P2027 and related codes do not return.

The repair should be considered successful only when the sensor circuit operates within specification and P2027 does not return.

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What Happens If P2027 Is Ignored?

P2027 generally does not cause immediate engine failure.

The vehicle may continue to operate normally.

However, an unresolved EVAP sensor fault can affect:

• EVAP system monitoring

• Emissions diagnostics

• Fuel-vapor control

• Readiness monitors

• Check Engine Light status

If the vehicle also has an actual fuel or vapor leak, the situation can be more serious.

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Can You Drive With P2027?

In most cases, a vehicle with P2027 can still be driven if it starts and operates normally.

The fault generally concerns an EVAP temperature-sensor circuit rather than a system required for basic engine operation.

However, the problem should still be diagnosed.

Do not ignore the problem if the vehicle also has:

• Strong gasoline smell

• Visible fuel leakage

• Difficult refueling

• Fuel-system problems

• Multiple EVAP codes

• Starting problems

• Rough engine operation

A strong gasoline smell or visible fuel leak requires prompt inspection.

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Is P2027 a Serious Code?

P2027 is generally considered a low-to-moderate severity diagnostic trouble code.

It normally does not cause immediate loss of engine power or prevent the vehicle from starting.

However, the high-voltage sensor fault can prevent the EVAP system from being monitored correctly and may prevent emissions-related readiness monitors from completing.

The severity is greater if P2027 occurs together with:

• Fuel leaks

• Strong fuel-vapor smell

• EVAP pressure problems

• Multiple EVAP faults

• Fuel-system problems

Therefore, the code should be diagnosed even if the vehicle appears to drive normally.

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P2027 vs. P2026

P2026, P2027, and P2028 are closely related EVAP fuel vapor temperature sensor codes.

Code	General Meaning
P2026	EVAP Fuel Vapor Temperature Sensor Range / Performance
P2027	EVAP Fuel Vapor Temperature Sensor Circuit High Voltage
P2028	EVAP Fuel Vapor Temperature Sensor Circuit Intermittent

The distinction is important.

P2026 indicates that the sensor signal is outside its expected operating range or performance characteristics.

P2027 indicates that the electrical signal is specifically too high.

P2028 indicates that the sensor circuit signal is intermittent.

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P2027 vs. P2028

Both codes concern the EVAP fuel vapor temperature sensor circuit, but they describe different electrical behavior.

P2027 → High voltage

The control module detects a voltage above the expected circuit range.

P2028 → Intermittent

The circuit or signal becomes abnormal intermittently.

An intermittent open connection can sometimes produce a high-voltage condition while the circuit is open and later result in an intermittent code as the connection comes and goes.

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P2027 vs. P2029 and P2030

These codes concern different systems.

Code	General Meaning
P2027	EVAP Fuel Vapor Temperature Sensor Circuit High Voltage
P2028	EVAP Fuel Vapor Temperature Sensor Circuit Intermittent
P2029	Fuel-Fired Heater Disabled Malfunction
P2030	Fuel-Fired Heater Performance Malfunction

P2027 concerns the EVAP fuel vapor temperature sensor circuit.

P2029 and P2030 concern a fuel-fired heater system.

Therefore, P2027 should not automatically be diagnosed as a fuel-fired heater problem.

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P2027 vs. P2045

P2045 also contains the words "Circuit High", but it concerns a different system.

P2027 refers to the EVAP fuel vapor temperature sensor circuit.

P2045 refers to the reductant temperature sensor circuit.

The two codes should not be confused simply because both describe a high electrical signal.

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How to Prevent P2027

Not every sensor or electrical failure can be prevented, but proper maintenance can reduce the risk.

Recommended practices include:

• Inspect EVAP wiring during routine service.

• Keep wiring secured away from exhaust heat.

• Repair damaged wiring promptly.

• Check EVAP connectors for corrosion.

• Prevent moisture from entering connectors.

• Inspect EVAP hoses regularly.

• Avoid damaging EVAP wiring during fuel-tank repairs.

• Keep harnesses away from sharp metal edges.

• Secure wiring against excessive vibration.

• Address gasoline smells immediately.

• Repair fuel-vapor leaks promptly.

• Use the correct replacement sensor.

• Make sure sensor connectors are fully seated.

• Avoid incorrect wiring repairs.

• Do not ignore Check Engine Light warnings.

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Final Thoughts

P2027 Evaporative Emissions (EVAP) Fuel Vapor Temperature Sensor Circuit High Voltage indicates that the vehicle's control module has detected an abnormally high electrical voltage in the EVAP fuel vapor temperature sensor circuit.

The most important point is that "High Voltage" does not necessarily mean that the fuel vapor temperature itself is too high.

The high signal may instead be caused by:

• Faulty fuel vapor temperature sensor

• Open sensor circuit

• Broken signal wire

• Disconnected connector

• Corroded terminals

• Poor terminal tension

• Short to voltage

• Damaged wiring

• Missing sensor ground

• Incorrect reference voltage

• Moisture intrusion

• Wiring chafing

• Heat damage

• Control-module problems

• Software or calibration issues

An open circuit is particularly important to check because a disconnected sensor or broken signal wire can cause the circuit voltage to rise toward the reference voltage.

The correct diagnostic approach is therefore to determine whether the high voltage originates from the sensor itself or from the electrical circuit.

A technician should scan for additional codes, review freeze-frame data, monitor live sensor readings, inspect the sensor and connector, test for an open circuit, verify reference and supply voltage, check the sensor ground, test for shorts to voltage, inspect the harness, and compare sensor resistance with manufacturer specifications where applicable.

The sensor should not automatically be replaced simply because P2027 is stored.

Likewise, the high-voltage condition should not automatically be interpreted as excessive fuel vapor temperature.

In most cases, P2027 does not prevent normal vehicle operation. However, it can interfere with EVAP emissions monitoring and may prevent emissions-related readiness monitors from completing.

Once the underlying fault has been repaired, the code should be cleared and the vehicle should be operated through the appropriate diagnostic conditions to confirm that the sensor circuit remains within specification and P2027 does not return.