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DTC codes / U06xx · Network communication / U0603

U0603Lost Communication With Fuel Pressure Sensor A

U0603 is a generic communication fault indicating that a control module on the vehicle's controller area network (CAN) bus has stopped receiving valid messages from the fuel pressure sensor designated as Sensor A. The module that sets this code has detected a loss of the periodic data signal that the sensor normally broadcasts, which can be caused by wiring faults, sensor failure, or network communication problems.

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

Symptoms you may notice

  • Illumination of the check engine light or a dedicated service message on the dashboard
  • Often no symptoms besides the warning light, especially if the sensor signal is only intermittently lost
  • Rough running, hesitation, or a stumble under acceleration if the fuel pressure reading is missing when the engine needs it
  • Reduced engine power or limp-home mode triggered by the module that lost the signal
  • Difficulty starting or an engine that stalls shortly after start-up in more severe cases
  • Poor fuel economy or increased emissions as the module substitutes a default fuel pressure value

Common causes, most likely first

  1. Damaged, corroded, or disconnected wiring or connector at the fuel pressure sensor A or along its harness
  2. Failed fuel pressure sensor A that no longer transmits data on the CAN bus
  3. Open or shorted CAN data lines (CAN high or CAN low) between the sensor and the module that monitors it
  4. Poor ground connection or power supply fault at the sensor or the module that sets the code
  5. A faulty control module that is unable to receive or process the sensor message correctly
  6. Software or calibration issue in the module that interprets the fuel pressure sensor data
  7. Aftermarket accessories or poor previous repairs that disturb the CAN bus wiring or introduce interference

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes, then check for related communication codes in other modules to see if the fault is isolated to fuel pressure sensor A
  2. Inspect the fuel pressure sensor A connector and harness for corrosion, loose pins, chafing, or signs of rodent damage, and repair as needed
  3. Measure reference voltage and ground at the sensor connector with the key on, engine off, to confirm the sensor is receiving power and ground
  4. Check the CAN bus data lines for continuity, shorts to ground, or shorts to voltage between the sensor and the module, using a wiring diagram for the specific vehicle
  5. If wiring and power are good, substitute a known-good fuel pressure sensor A and clear the code to see if communication returns
  6. Perform a module reset or software update if the manufacturer has published a technical service bulletin for this communication fault
  7. After repairs, clear all codes and drive the vehicle through a complete drive cycle to verify that U0603 does not return

Why fuel pressure sensor A loses communication

  • A loose or corroded ground connection at the chassis can cause the sensor's CAN messages to drop out intermittently, setting U0603 without any visible wiring damage at the sensor itself.
  • Some vehicles use a dedicated serial data line for the fuel pressure sensor rather than the main CAN bus, so a scan tool that only checks the main bus may miss the fault entirely.
  • U0603 can be set by a low battery or charging system fault that causes modules to reboot and briefly lose communication, so always check battery voltage and charging output before replacing parts.
  • Aftermarket remote starters, alarms, or poorly installed accessories that tap into CAN wiring are a common hidden cause of communication codes like U0603.
  • The code does not always mean the sensor is dead; a module that is failing to wake up or a network gateway issue can also prevent the fuel pressure message from being received.

Can I keep driving with U0603?

You can usually drive the vehicle to a repair shop if the only symptom is the warning light and the engine runs normally, but avoid heavy acceleration or towing until the fault is repaired. If the engine runs rough, stalls, or enters limp mode, stop driving and have the vehicle towed to prevent damage or unsafe operation.

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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