U0642 code meaning
Lost Communication With EVAP System Pressure Sensor/Switch Circuit B
Network system Generic code U06xx codes Check engine light
What U0642 means
A second EVAP pressure sensor, B, appears where one reading is not enough, for instance when tank and canister are separated by an isolation valve and each side needs its own value, as in sealed tanks of plug-in hybrids that see higher pressures. Which location is called B is up to the manufacturer. U0642 is the lost-communication code for this sensor when it reports digitally; its analog counterpart logs P24D5 to P24D9. No manufacturer documents U0642 publicly. Because CARB 1968.2 (e)(15.2.1)(B)(i) demands a separate code for a digital input that stops talking, the code exists independently of U0641. While B is silent, the controller cannot compare both sides or check the isolation valve, so the leak test is suspended and a MIL is to be expected.
U0642 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0642
- MIL on
- EVAP monitor incomplete
- On sealed tanks possibly a delayed fuel door release
Common causes of U0642
- Most likelySignal, supply or ground line to sensor B open or chafed
- PossibleCorroded or unplugged connector at sensor B
- PossibleSensor B electronics failed
- Less likelyReceiving controller input or software fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
EVAP pressure sensor bVehicle bus wiring
What each part of U0642 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 42 | The exact fault in that area. |
What to do next
- Note U0642 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 U0642
What does U0642 mean?
U0642 means "Lost Communication With EVAP System Pressure Sensor/Switch Circuit B". A second EVAP pressure sensor, B, appears where one reading is not enough, for instance when tank and canister are separated by an isolation valve and each side needs its own value, as in sealed tanks of plug-in hybrids that see higher pressures. It is a generic code, so it means the same on every make.
Is it safe to drive with U0642?
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 U0642 fail an emissions test?
Yes, it can. U0642 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 U0642 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U0642 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.