U3508

What it means

U3508 is a generic code meaning a control module has judged the voltage on its input power 'C' circuit to be outside the expected range or not performing as it should. The module monitors its own supply voltage and set the code when the reading was too high, too low, unstable or implausible. Which supply feed is 'C' and which module reports it depends on the make, model and system, so check the vehicle-specific wiring information.

Symptoms

• Warning lights on the dashboard, or several systems reporting faults at once
• Intermittent loss of function from the affected module, such as a system dropping out and returning
• Other modules logging communication or low-voltage codes
• Hard starting or a weak battery condition
• Flickering lights or erratic gauges
• No obvious symptoms, with the code found only during a scan

Possible causes

• Weak or poorly charged battery, or a poor battery terminal connectionlikely
• Charging system fault causing low or excessive voltage, such as a worn alternator or faulty regulationlikely
• Corroded, loose or damaged connector, pin or earth connection on the module's power or ground circuitlikely
• Open circuit, high resistance or short in the power supply wiring, fuse or relay feeding the modulepossible
• Previous repair work, accessories or aftermarket wiring interfering with the supplypossible
• Faulty control module with an internal power supply or monitoring faultrare
• Outdated or faulty module software, where the manufacturer lists it as a known causerare

How to diagnose

1. Scan all modules, record every stored code and the freeze frame data, and note which module set U3508 and whether it is current or historic
2. Check the battery's state of charge and condition, and inspect the terminals and main cables for looseness and corrosion
3. Measure battery voltage with the engine off, while cranking and while running, to confirm the charging system is within specification
4. Look up the circuit that U3508 refers to in the vehicle-specific wiring information, and identify the fuses, relays and earths for that module
5. Inspect the module's connectors and related earth points for corrosion, water ingress, bent pins and chafed wiring
6. Voltage-drop test the power and earth feeds to the module under load, and wiggle-test the harness while watching live data
7. Check for outstanding technical bulletins or software updates for the affected module and model
8. Clear the codes, road test and rescan to see whether the fault returns

How to fix

• Charge or replace the battery, and clean and tighten the terminals and earth straps
• Repair or replace the alternator or charging control components if output is out of specification
• Repair corroded or damaged connectors, terminals and wiring, and restore good earth connections
• Replace faulty fuses, relays or power supply wiring once the cause of the failure is found
• Remove or correct any faulty aftermarket wiring or accessories affecting the supply
• Update the module software where an official update addresses the fault, or replace the module only after the supply and earth are proven good

Can I keep driving?

Nearby codes

• U3507GenericControl Module Input Power B Circuit Intermittent/Erratic
• U3509GenericControl Module Input Power C Circuit Low