U355F: Cathode Backpressure Valve Control Circuit

Generic electrical fault on the cathode back-pressure valve control. The valve regulates pressure on the cathode (air) side of the fuel cell stack.

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

Most likely causes

• Valve actuator failed
• Gateway module routing CAN messages incorrectly
• CAN terminating resistor (120 Ω) drifted out of spec

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the battery and terminals, and read the codes from all control modules with a multi-system scanner
2. Identify which control module is not responding and check its fuses, power supply, and grounds
3. Disconnect add-on accessories, such as alarms or trackers, and read the codes again
4. Inspect the network connectors for moisture or bent pins
5. Measure the network's resistance and signal using the manufacturer's wiring diagram

Good to know

• Repair difficulty: hard
• It can trigger limp mode.

What each character of U355F means

• U: Communication network
• 3: Generic code: same on every make
• 5: Subsystem depends on the code range
• 5F: Specific fault in that system

Frequently asked questions

Can I keep driving with code U355F?

It depends on which control module has dropped out. If it affects the engine, brakes, or steering, do not continue your trip: call for roadside assistance.

What causes code U355F?

The most common causes are: valve actuator failed; gateway module routing CAN messages incorrectly; cAN terminating resistor (120 Ω) drifted out of spec.

Sources

• github.com: dtc database
• en.wikipedia.org: Proton exchange membrane fuel cell

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.