U066F: Lost Communication With Low Pressure Fuel System Sensor

What it means

The vehicle bus reports loss of communication with smart low-pressure fuel system sensor. Lift-pump pressure feedback is unavailable; high-pressure pump and injection switch to a fail-safe map.

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

The low-pressure fuel system sensor reports lift-pump pressure to the vehicle network so the engine controller can account for fuel supply before the high-pressure pump and injectors. The control module sets U066F when communication with this sensor is lost, forcing fuel control to use a fail-safe map and potentially limiting power.

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. Scan all modules for communication faults and review freeze-frame data for fuel pressure, engine load, and other devices that dropped offline at the same time.
2. Check scan-tool data to confirm whether the low-pressure fuel system sensor is online and whether its pressure reading is available.
3. Inspect the sensor connector and harness along the low-pressure fuel lines for looseness, corrosion, fuel contamination, or damage.
4. Use the manufacturer's wiring information to check sensor power and ground and test the network wiring for opens, shorts, or poor connections.
5. If power, ground, and wiring are sound, test communication at the sensor and determine whether the sensor module has failed.

Common fixes

• Reconnect or clean the low-pressure fuel sensor connector and repair damaged wiring.
• Restore a missing or poor power or ground connection to the sensor.
• Repair an open or short in the network wiring to the low-pressure fuel system sensor.
• Replace the sensor if its power, ground, and network connections are good but it remains offline.

Can I keep driving?

Because the engine may be in a reduced-power fuel fail-safe mode, avoid high speeds, hard acceleration, and towing; arrange prompt diagnosis. If the engine stumbles, stalls, or cannot maintain safe speed, pull over and stop driving.