U0655 code meaning
Lost Communication With Diesel Intake Air Flow B Position Sensor
Network system Generic code U06xx codes Check engine light
What U0655 means
Some diesels carry a second intake air flow valve, labelled B; which flap gets that letter depends on the engine layout and the maker. When its angle sensor is a digital SENT unit, U0655 reports that the engine controller no longer receives usable position frames from it. No manufacturer documents this code in public. GM's 2025 diesel tables give SENT link codes only to valve A (U0654, Type A, 6.25 ms checks), and CARB requires a separate code whenever a digital input stops communicating. Analog sensor faults on the B side are P2396 to P239A, drive faults P2390 to P2395. Expect the flap to be switched off and left to its spring, with EGR control and regeneration limited and a likely MIL on emission-certified engines.
U0655 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0655
- Check engine light
- Particulate filter regeneration postponed or blocked
- Little change in drivability in many cases
Common causes of U0655
- Most likelyContaminated or loose connector at throttle unit B
- PossibleSignal, supply or ground wire to sensor B damaged
- PossibleDigital position sensor of valve B failed
- Less likelyEngine controller input fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Diesel intake airflow position sensor bVehicle bus wiring
What each part of U0655 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 55 | The exact fault in that area. |
What to do next
- Note U0655 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 U0655
What does U0655 mean?
U0655 means "Lost Communication With Diesel Intake Air Flow B Position Sensor". Some diesels carry a second intake air flow valve, labelled B; which flap gets that letter depends on the engine layout and the maker. It is a generic code, so it means the same on every make.
Is it safe to drive with U0655?
Drive gently and only to a workshop. With U0655 the car can go into limp mode (reduced power) to protect itself.
Will U0655 fail an emissions test?
Yes, it can. U0655 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 U0655 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will U0655 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.