U3549: Hydrogen Tank High Pressure Sensor 1 Circuit

What it means

Generic electrical fault on the high-pressure hydrogen tank pressure sensor 1 (typical operating range up to 700 bar on FCEVs).

At a glance

• Usually lights the warning light of the system that lost communication
• The engine or gearbox may go into limp mode

How it works

The hydrogen tank high-pressure sensor 1 reports tank pressure to the vehicle's fuel-cell control system. This code identifies an electrical fault in sensor 1's circuit, so the module may not be able to rely on that pressure signal; it does not by itself establish that tank pressure is actually high or low.

Common causes

Most likely first.

1. Pressure sensor failed
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

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 the fuel-cell, gateway, and other available modules and save freeze-frame data to see whether U3549 is accompanied by pressure-sensor or communication faults.
2. Compare live data for hydrogen tank pressure sensor 1 with other available pressure information and check whether the reading is missing, implausible, or intermittent.
3. Visually inspect the sensor 1 connector and accessible low-voltage wiring for damage, poor seating, corrosion, or signs of moisture; do not disturb hydrogen plumbing.
4. Check sensor 1 circuit power, ground, signal, and continuity using the vehicle manufacturer's wiring diagram and specifications.
5. If the circuit tests correctly, follow the manufacturer's procedure to assess sensor 1 and then check for a confirmed gateway or CAN communication fault.

Common fixes

• Reconnect or repair a loose or damaged sensor 1 electrical connector.
• Repair damaged sensor 1 wiring or a confirmed power or ground fault.
• Replace hydrogen tank pressure sensor 1 if its circuit is sound and the sensor fails the specified test.
• Repair a confirmed gateway or network fault affecting the pressure data.

Can I keep driving?

If the vehicle shows a fuel-cell warning, reduced power, or a hydrogen-system shutdown warning, stop in a safe place and follow the vehicle's instructions; unreliable tank-pressure data can limit or stop operation. Do not inspect or loosen high-pressure hydrogen components yourself.