U3502

What it means

U3502 means a control module has detected that its input power supply (power feed 'A') is higher than the acceptable range. The module monitors its own supply voltage and set the code when it stayed too high. Which module stored it, and the exact voltage limits, depend on the vehicle.

Symptoms

• Battery or charging warning light on the dashboard
• Headlights or interior lights unusually bright or flickering
• Other warning lights or communication fault codes appearing at the same time
• Intermittent or erratic operation of electronic systems
• Battery needing frequent water top-ups (where applicable), or a hot or swollen battery
• Possible limp-mode or system shutdown in the affected module

Possible causes

• Charging system overvoltage, such as a faulty alternator regulator or faulty charge controllikely
• Poor or corroded earth connection or battery terminal causing abnormal voltage readings at the modulelikely
• Faulty or incorrect battery, or a battery with a failing cellpossible
• Recent jump start, external charger or aftermarket electrical equipment applying excess voltagepossible
• Damaged wiring, connector or fuse/relay feed to the affected modulepossible
• Internal fault in the control module's power supply or its voltage monitoringrare
• Outdated software in the module or charge control system (only where the manufacturer lists it as a known issue)rare

How to diagnose

1. Read all stored codes in every module and note which module set U3502, plus any freeze frame or voltage data and any related charging or communication codes
2. Ask about recent jump starts, battery charging, battery replacement or fitted accessories
3. Visually inspect battery terminals, main earth straps, fuses and the connectors on the affected module for corrosion, looseness or damage
4. Measure battery voltage with the engine off, then running at idle and at raised revs, and compare with the manufacturer's specification (smart charging systems vary the voltage by design)
5. Check the alternator output and regulator operation, including any charge control signal from the engine control unit, following the model's procedure
6. Test the battery state of health and check the voltage drop across the positive and earth circuits under load
7. Check the supply voltage and earth at the affected module's connector against the wiring diagram
8. Check for manufacturer software updates or technical bulletins for the module, then clear the code and road test to see if it returns

How to fix

• Repair or replace the alternator or its regulator if output voltage is above specification
• Clean, tighten or repair battery terminals and earth connections
• Replace the battery if it is faulty or of the wrong type, and confirm the charging system is healthy afterwards
• Repair damaged wiring or connectors in the power feed to the affected module
• Remove or correct faulty aftermarket electrical equipment or charger connections
• Replace or update the control module only after the supply voltage is proven correct and the manufacturer confirms a fault or a software fix

Can I keep driving?

Nearby codes

• U3501GenericControl Module Input Power A Circuit Low
• U3503GenericControl Module Input Power A Circuit Intermittent/Erratic