U0603: Lost Communication With Fuel Pressure Sensor A

What it means

The vehicle bus reports loss of communication with smart fuel pressure sensor A (typically common-rail or low-pressure side). The ECM loses its actual rail-pressure feedback for closed-loop control.

At a glance

• Usually lights the warning light of the system that lost communication
• Affects emissions; the car can fail an emissions test
• The engine or gearbox may go into limp mode

How it works

Fuel pressure sensor A reports pressure over the vehicle network so the engine controller can regulate fuel delivery using feedback. U0603 sets when communication with sensor A is lost, leaving that pressure channel unavailable and potentially forcing a fail-safe strategy.

Common causes

Most likely first.

1. Bus wiring open or shorted
2. Module without power or ground
3. Module failed

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Record freeze-frame data and scan all modules for related fuel-pressure, engine-control, and network codes before clearing faults.
2. Check whether the engine starts, idles, or accelerates poorly and whether live data for fuel pressure sensor A is missing or replaced by a default value.
3. Inspect sensor A’s connector and accessible harness for looseness, corrosion, fuel contamination, chafing, or heat damage.
4. Check the sensor’s specified power, ground, and network wiring to the manufacturer’s specification, and look for other modules or sensors on the same bus that have also dropped offline.
5. If power, ground, and wiring are sound, test sensor A’s communication and verify its configuration before diagnosing the engine controller.

Common fixes

• Repair a loose, corroded, contaminated, or damaged sensor A connector or wiring.
• Restore the sensor’s specified power or ground.
• Repair a shared network fault if other devices have also lost communication.
• Replace fuel pressure sensor A if communication tests confirm it has failed.
• Repair or reconfigure the controller only if vehicle-specific testing points to it.

Can I keep driving?

Avoid driving if the engine stalls, loses power, starts unpredictably, or shows a fuel-system warning; arrange a tow if it cannot run safely. Loss of fuel-pressure feedback can cause poor fueling, stalling, or reduced power, so do not attempt high-speed or heavy-load driving.