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DTC codes / U06xx · Network communication / U0604

U0604Lost Communication With Fuel Pressure Sensor B

U0604 is a communication fault where the module that monitors fuel pressure sensor B stops receiving valid data over the vehicle's controller area network (CAN) bus. The computer has detected that the expected periodic message from the sensor or its control module is missing or corrupted, not that the sensor itself has failed electrically.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaNetwork communication

Symptoms you may notice

  • Illumination of the check engine light or a dedicated service warning, often with no other noticeable symptoms.
  • Intermittent or complete loss of fuel pressure readings on a dashboard gauge or scan tool live data stream.
  • Rough running, hesitation, or stalling if the missing signal is used for fuel pump control or injector timing.
  • Reduced engine power or limp-home mode triggered by the module that lost the sensor data.
  • A stored code in multiple modules indicating communication loss with the same sensor or its control module.

Common causes, most likely first

  1. Damaged, corroded, or loose wiring or connector pins in the circuit between fuel pressure sensor B and its control module.
  2. Failed fuel pressure sensor B or its integrated electronics, causing it to stop transmitting on the CAN bus.
  3. A faulty control module that the sensor communicates through, such as the fuel pump control module or powertrain control module (PCM).
  4. CAN bus wiring faults, including opens, shorts, or excessive resistance on the communication lines.
  5. Low battery voltage or a weak charging system causing modules to drop offline intermittently.
  6. Water intrusion or heat damage at the sensor connector or along the harness routing.
  7. Aftermarket accessories or poor previous repairs introducing electrical noise or incorrect bus termination.

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes in every module, then check for service bulletins or software updates related to communication faults on this bus.
  2. Inspect the fuel pressure sensor B connector and harness for corrosion, chafing, or loose pins, and perform a wiggle test while watching live data.
  3. Measure battery voltage and charging system output to rule out low-voltage dropouts before condemning any module.
  4. Check CAN bus resistance and voltage levels at the diagnostic connector to confirm the bus is healthy and properly terminated.
  5. Substitute a known-good fuel pressure sensor B or its control module only after wiring and power checks pass, then clear codes and verify communication returns.
  6. If the fault persists, perform a guided diagnostic routine for the specific module network and check for intermittent opens with a lab scope on the CAN lines.

Communication loss is not always the sensor

  • A U0604 often sets because the module that owns fuel pressure sensor B lost power or ground momentarily, not because the sensor itself failed.
  • Technicians frequently replace the sensor only to find a corroded connector pin or a chafed harness section causing the intermittent communication loss.
  • This code can be stored alongside misfire or fuel trim codes that mislead diagnosis toward fuel delivery when the real issue is a data bus fault.
  • Some vehicles use the same bus for multiple pressure sensors, so a single shorted sensor can take down communication for several components and set multiple U-codes.
  • Aftermarket electrical accessories or improper jump-starting can introduce voltage spikes that temporarily drop modules off the bus and set U0604 without a hard failure.

Can I keep driving with U0604?

You can usually drive carefully to a repair shop if the engine runs normally, but avoid heavy acceleration or towing because a lost fuel pressure signal may cause stalling or limp mode. Stop driving if the engine runs rough, stalls, or shows reduced power, as fuel delivery may be compromised.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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