Poor connection or corrosion at the ignition switch, its connector or the ignition/start relay; Low battery voltage or weak battery causing voltage dips during cranking; Loose, corroded or damaged battery terminals, earths or main power feeds; Wiring fault in the ignition-on or start signal circuit to the affected module (open circuit, high resistance, short or chafing); Worn ignition switch or faulty start/ignition relay giving an inconsistent signal; Faulty body control module, fuse box or the affected control module's internal input circuit; Outdated or faulty software in the affected module, where the manufacturer has documented this as a cause.

U3023

Control Module Input Power Circuit A - Ignition Input On/Start Circuit Correlation.

Generic
Network
Generic code
Medium severity

How this code is built

U: SystemNetwork
3: Defined bySAE, the same on every car
0: AreaNetwork area 0
23: FaultThe specific fault in that area

What it means

U3023 is a generic network and module code meaning a control module has found that its ignition input (on/run) and its start (crank) input do not agree. For example, it may see a crank signal without a valid ignition-on signal, or the two inputs may change state in an implausible order. The module sets the code when this correlation check fails. The exact inputs compared and the set conditions vary by manufacturer, model and module.

Symptoms

Warning lights on the dashboard, possibly with a message about the electrical system or starting
Engine cranks but does not start, or does not crank at all
Intermittent no-start or stalling, especially when the key is turned or the engine is cranking
Other modules on the vehicle setting communication or low voltage codes at the same time
Erratic dashboard behaviour or accessories cutting out when cranking

Possible causes

Poor connection or corrosion at the ignition switch, its connector or the ignition/start relaylikely
Low battery voltage or weak battery causing voltage dips during crankinglikely
Loose, corroded or damaged battery terminals, earths or main power feedslikely
Wiring fault in the ignition-on or start signal circuit to the affected module (open circuit, high resistance, short or chafing)possible
Worn ignition switch or faulty start/ignition relay giving an inconsistent signalpossible
Faulty body control module, fuse box or the affected control module's internal input circuitrare
Outdated or faulty software in the affected module, where the manufacturer has documented this as a causerare

How to diagnose

Read all stored codes and freeze frame data, noting which module set U3023 and what voltage and ignition state were recorded, then check for other power, voltage or communication codes
Test battery condition and charging system output, and check battery terminal tightness and cleanliness
Inspect fuses, relays and their sockets for the ignition and start circuits, using the wiring diagram for the specific model
Inspect the connectors at the affected module and at the ignition switch for corrosion, pushed-out pins, moisture or heat damage
Check the main earths and power feeds for voltage drop under load, including while cranking
Monitor the ignition-on and start input status in live data while turning the key through each position and cranking, looking for dropouts or mismatched states
Test the ignition and start signal circuits for continuity, short to earth or to power, and high resistance, following the manufacturer procedure
Check for manufacturer service bulletins or available software updates for the affected module

How to fix

Clean and tighten battery terminals and earth connections, and repair any damaged main power feeds
Replace a weak or failing battery, and repair the charging system if output is out of specification
Repair or replace damaged wiring, terminals or connectors in the ignition-on or start circuit
Replace a faulty ignition switch or ignition/start relay confirmed by testing
Update the module software only if the manufacturer lists it as a fix for this fault
Replace the affected control module only after power, earth, wiring and signal inputs have been proven good, and code it as required

Can I keep driving?

Medium severity

If the car starts and runs normally, it can be driven carefully for a short time while you arrange a repair, but it may fail to start or stall without warning. If it stalls, loses power or won't start reliably, stop driving it and have it checked.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.