U3035

What it means

U3035 means a control unit received a communication authentication signal that was invalid or corrupted. The module checks messages from another module on the network, and the authentication data was not in the expected format or value. U3xxx codes are largely manufacturer-defined, so which modules and functions are involved depends on the model.

Symptoms

• Warning lights on the dashboard, depending on which module logged the fault
• Engine cranks but will not start, or starts and then stops (where immobiliser or security authentication is involved)
• Key or keyless entry not recognised
• Other communication fault codes stored in several modules
• Some features unavailable, such as driver aids or remote functions
• Intermittent faults that appear after battery disconnection or low voltage

Possible causes

• Low or unstable battery or supply voltage corrupting network messageslikely
• Damaged wiring, poor connections or corrosion on the communication networklikely
• A module replaced or repaired without the correct security pairing or adoption procedurepossible
• Mismatched or outdated software or configuration between modulespossible
• Faulty control unit sending or checking the authentication datapossible
• Faulty gateway module or key or transponder system componentrare

How to diagnose

1. Read all stored and pending codes from every module, and note the freeze frame data and which module set U3035
2. Check battery condition and charging voltage, as low voltage commonly causes network faults
3. Find out whether any module has recently been replaced, repaired, reprogrammed or had the battery disconnected
4. Inspect the connectors, earths and wiring on the affected modules and the network for damage, water ingress and corrosion
5. Check the network for short or open circuits and correct signal levels, following the manufacturer's wiring information
6. Check whether the affected modules have software or configuration mismatches, using manufacturer-approved diagnostic equipment
7. Clear the codes and retest to see whether U3035 returns, and whether it is current or historic
8. Check for manufacturer technical bulletins relating to this code on your model and engine

How to fix

• Charge or replace a weak battery and repair any charging system faults
• Repair or replace damaged wiring, connectors or earths on the network
• Carry out the manufacturer's security pairing or adoption procedure on any replaced module
• Update or correct the module software and configuration where the manufacturer specifies a fix for this fault
• Replace a confirmed faulty control unit or gateway, then complete the required setup procedure

Can I keep driving?

Nearby codes

• U3034GenericCommunication Authentication Key/Certificate Missing/Invalid
• U3036GenericCommunication Authentication Signal Performance