U0604 code meaning
Lost Communication With Fuel Pressure Sensor B
Network system Generic code U06xx codes Check engine light
What U0604 means
Sensor B is the second fuel pressure measuring point, for example a low-pressure sensor in the feed line of a direct injection engine or a second rail on V engines; which pressure it reads depends on the maker. U0604 flags that this digital sensor has stopped sending valid SENT frames to the engine controller. Nobody publishes a manufacturer description for this code. By analogy with Ford's SENT checks for oil and filter pressure sensors, the controller would look for driver errors, a line held high or low or missing frames and confirm after a few seconds. CARB 1968.2 requires separate lost-communication codes for coded digital inputs. P018A is the analog circuit code for sensor B, U0603 the counterpart for sensor A. Depending on the role, pump control or the second rail falls back to defaults.
U0604 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.3 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0604
- Check engine light on
- Hesitation or reduced power under load
Common causes of U0604
- Most likelyDamaged signal, supply or ground wire to sensor B
- PossibleSensor B failed internally
- Less likelySensor A and B connectors swapped or loose
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Fuel pressure sensor bSensor wiring
What each part of U0604 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 04 | The exact fault in that area. |
What to do next
- Note U0604 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 U0604
What does U0604 mean?
U0604 means "Lost Communication With Fuel Pressure Sensor B". Sensor B is the second fuel pressure measuring point, for example a low-pressure sensor in the feed line of a direct injection engine or a second rail on V engines; which pressure it reads depends on the maker. It is a generic code, so it means the same on every make.
Is it safe to drive with U0604?
Drive gently and only to a workshop. With U0604 the car can go into limp mode (reduced power) to protect itself.
Will U0604 fail an emissions test?
Yes, it can. U0604 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 U0604 to fix?
Difficulty: medium. A typical repair takes 0.3 to 2 hours of work. This is a job for a workshop.
Will U0604 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.