U0640 code meaning
Lost Communication With EVAP Fuel Vapor Temperature Sensor Circuit
Network system Generic code U06xx codes Check engine light
What U0640 means
Many fuel tank pressure senders also measure the temperature of the vapor in the tank, and when such a sender reports digitally, typically over SENT, both values share one data stream. U0640 is stored when the engine controller no longer receives valid temperature data from this sensor. Despite the word circuit in the title, the fault concerns the digital link; an analog vapor temperature sensor reports wiring faults as P2024 to P2028. Audi documents U0640 together with U0641 for 2021–2023 A4 and A5 models with the 2.0 TFSI EA888: electrical interference on the vent system signal sets both codes sporadically, the cure is swapping two wires of a twisted bundle in the harness, and a new sender does not help. The MIL comes on, while the car drives normally.
U0640 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0640
- Check engine light on
- Often stored together with U0641
- Evaporative system monitor does not complete
Common causes of U0640
- Most likelyInterference or chafing on the shared signal line of the tank pressure/temperature sender
- PossibleLoose or corroded connector at the tank sender
- Less likelyElectronics of the sender failed (only if the code is stored permanently)
- Less likelyEngine controller software or input fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
EVAP vapor temp sensorVehicle bus wiring
What each part of U0640 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 40 | The exact fault in that area. |
What to do next
- Note U0640 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0640
What does U0640 mean?
U0640 means "Lost Communication With EVAP Fuel Vapor Temperature Sensor Circuit". Many fuel tank pressure senders also measure the temperature of the vapor in the tank, and when such a sender reports digitally, typically over SENT, both values share one data stream. It is a generic code, so it means the same on every make.
Is it safe to drive with U0640?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U0640 fail an emissions test?
Yes, it can. U0640 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U0640 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will U0640 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.