My fuel gauge went wrong at the same time. Are the two related?

Almost certainly, and that is genuinely good news. The vapor temperature sensor and the fuel level sender leave the tank through the same connector, so a single corroded or unlatched plug takes both out together. Two symptoms arriving at once points at one repair rather than two, and it tells you where to look before you spend anything on diagnosis.

What does a water leak in the cabin have to do with an emissions code?

More than it sounds like. On many vehicles the tank-top connector is reached through an access panel under the rear seat or boot floor, which sits at the lowest point of the rear floorpan. Water from a blocked sunroof drain, a failed door seal or a leaking rear screen collects there and sits on the connector. That corrodes terminals through rather than merely bridging them, which is exactly the open circuit this code reports. Fixing the connector without fixing the leak just resets the clock.

Why does the voltage reading matter before I plug anything back in?

Because two very different faults look identical on the scan tool. A signal sitting near the reference voltage is an open circuit — inexpensive and harmless. A signal at battery voltage means the wire has found a power feed, which puts twelve to fourteen volts onto an input built for about five and can damage the module's input circuitry. Measuring before reconnecting is what stops a wiring fault from turning into a module fault.

Can I just keep driving with it?

Yes, and many people do for months without noticing anything. The vapor temperature reading only feeds the leak-detection monitor, which needs it to tell thermal expansion apart from a real leak. Without it the module skips the test. Nothing about running, economy or safety changes. What you lose is the ability to complete emissions readiness, which matters at inspection time and not before.

OBD-II trouble code

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

The circuit has come apart somewhere rather than touched something. Openings on this sensor cluster around two places — the connector on top of the tank and the sealed pass-through where the wires leave the pump flange — and both of them fail for reasons you can predict.

Low severityPowertrainEvaporative EmissionsDrivable short-term

Quick facts

System: Powertrain
Category: Evaporative Emissions
Severity: Low severity
Drivable: Usually safe to drive short-term
Repair cost range: $0 – $800
DIY difficulty: Advanced DIY

What does P2027 mean?

A high reading on this circuit is a broken connection, not a hot tank. The module holds the signal input up through an internal resistor and relies on the thermistor to pull it back down; take the thermistor out of the picture and the input has nothing left holding it, so it floats to the top. Every kind of break produces the same result — a severed signal wire, a lost ground, a terminal that has retreated into its cavity, a sensor that has failed open. The module cannot tell those apart, and neither can the code.

What it can tell you is where to look, because openings on this particular circuit are not randomly distributed. Two locations account for most of them, and both fail through a specific mechanism worth understanding before the tank comes down.

The first is the electrical connector on top of the fuel tank. On many vehicles that connector is reachable through an access panel under the rear seat cushion or under the boot floor, which sounds convenient and is actually the problem. That panel sits at the lowest point of the rear floorpan, and everything liquid that gets into the cabin ends up there. A blocked sunroof drain, a perished rear door seal, a leaking rear screen bond, a spilled drink, a wet dog — all of it runs downhill to the same place and pools on top of the access cover. Water sitting on a connector in a warm, enclosed, poorly ventilated space corrodes terminals from the outside in, and unlike the bridging corrosion that causes low-voltage faults, this kind eats the metal through. The green product it leaves behind is a poor conductor, so the failure it produces is an open circuit rather than a short. That is why cabin water leaks and this code belong in the same conversation.

The second is the pass-through in the pump module flange, where the wires cross from inside the tank to outside it. That seal has to hold fuel vapor in while carrying conductors across, and it is the point where warm vapor meets cooler outside air. Condensation forms there routinely. Over years the terminals on the inboard side corrode, or the moulded seal hardens, cracks and admits vapor and moisture directly into the connector body. This one is unforgiving because it is not repairable in place; the flange is part of the module assembly.

There is one variation worth measuring for before anything is reconnected. A signal wire touching a power feed will also read at the top of the range, but it puts twelve to fourteen volts onto an input designed for about five. The measurement separates them cleanly: a reading that settles near the reference voltage is an ordinary open circuit, while a reading at battery voltage is a short to power and needs finding before the module sees any more of it.

One diagnostic shortcut is specific to this circuit and costs nothing. The vapor temperature sensor's wires leave the tank in the same connector as the fuel level sender's. If the fuel gauge has also gone strange — reading empty, reading full, refusing to move — then the fault is almost certainly in that shared connector rather than in the sensor, and you have localised the job to a single component before touching a meter.

Common causes

Corroded terminals in the tank-top connector, most often on vehicles with a history of water getting into the rear footwell or boot
Signal wire broken open, frequently inside insulation that still looks perfect from the outside
Sensor ground open, which floats the input high exactly as a broken signal wire does
Terminal backed out of its cavity in the connector so it no longer meets the mating pin
Failed seal at the pump module flange pass-through, letting vapor and condensation reach the conductors
Thermistor failed internally open through age or thermal cycling
Connector left unlatched after fuel pump, sender or filler neck work
Signal wire shorted to battery voltage — uncommon, but the one version of this fault that can damage the module
Rodent-severed wire in the underbody run, which is worth checking on vehicles that sit for long periods

Symptoms

Check engine light on while the vehicle drives entirely normally
Fuel vapor temperature displayed at the extreme top of its range on a scan tool, or as an implausible fixed value
EVAP monitor stuck at not-ready and never completing
Fuel gauge misreading or stuck at the same time, which points straight at the shared tank-top connector
Damp rear carpet, a musty smell in the cabin or a known water leak in the vehicle's history
Fault that appeared shortly after fuel pump, sender or rear suspension work
Companion EVAP leak or purge codes stored because the monitor cannot run properly

Diagnostic steps

1.Check the fuel gauge first. It costs nothing and the sender shares the tank-top connector with this sensor, so a gauge that has also gone wrong localises the fault to that connector before any tool comes out.
2.Measure the actual signal voltage before reconnecting anything. Near the reference voltage means a plain open circuit. At battery voltage it is a short to power, and that must be found and cleared or the module input can be damaged.
3.Lift the rear seat cushion or boot floor and look for the access panel. Check for water, staining or corrosion on and around it — a cabin leak that has been dripping onto that cover is a common and completely fixable root cause.
4.Unlatch the connector and inspect both halves under good light. Look for green or white deposits, terminals sitting lower than their neighbours, and any pin that feels loose when the mating half is offered up.
5.With the sensor disconnected and the key on, confirm the reference voltage and a clean ground at the harness side. A missing ground produces this code just as reliably as a missing signal.
6.Jumper the signal pin to ground at the harness connector and watch the live value. If it drops to the bottom of the scale, everything from the connector back to the module is intact and the fault lies in the sensor or the flange pass-through.
7.Inspect the pump module flange where the wires cross into the tank. A hardened, cracked or fuel-swollen seal there means the module assembly is the repair, because that pass-through cannot be serviced separately.
8.Wiggle-test the underbody run while watching live data if the fault is intermittent. A conductor broken inside intact insulation shows up here and in no other test.
9.Fix any water leak you find before or alongside the electrical repair. Replacing terminals under a still-leaking sunroof drain guarantees a repeat visit.

Repair cost

$0 – $800

Zero is a real outcome here, not padding — a connector left unlatched after recent tank work costs nothing to reseat, and it is common enough to check first. From there, a terminal and pigtail repair on the tank-top connector runs $150 to $350. A broken wire in the underbody run is $100 to $300. Where the sensor or the flange pass-through has failed, the sensor is not sold separately on most vehicles, so the repair is a fuel pump and sender module at $200 to $600 plus 1.5 to 3 hours of access. If a cabin water leak caused the corrosion, budget separately for the drain, seal or bond that let the water in, because the electrical repair alone will not hold.

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DIY vs shop

This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.