Weak battery, poor battery terminal connections or low system voltage causing the module to see an invalid ignition on/start signal; Wiring damage, corrosion or loose connectors in the ignition on/start feed or output circuit; Faulty ignition switch, start button or related switch contacts (depends on vehicle); Faulty relay or blown fuse in the ignition or start circuit; Poor earth connection to the affected control module; Internal fault in the control module that drives or monitors the ignition output.

U302D

Ignition Output On/Start.

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
2D: FaultThe specific fault in that area

What it means

U302D is a network/control module code that the SAE J2012 definition lists as Ignition Output On/Start. A control unit has detected a fault with the ignition on/start output or the signal it expects for that state. It usually points to a wiring, power supply, switch or module problem rather than a single failed sensor. The exact circuit and which module sets the code depend on the vehicle.

Symptoms

Engine cranks slowly, intermittently or not at all
Engine starts then stalls, or cuts out while driving
Warning lights on the dashboard, possibly several at once
Dashboard or accessories not powering up correctly with the ignition on
Other modules reporting communication or ignition-related codes
Intermittent starting problems that come and go

Possible causes

Weak battery, poor battery terminal connections or low system voltage causing the module to see an invalid ignition on/start signallikely
Wiring damage, corrosion or loose connectors in the ignition on/start feed or output circuitlikely
Faulty ignition switch, start button or related switch contacts (depends on vehicle)possible
Faulty relay or blown fuse in the ignition or start circuitpossible
Poor earth connection to the affected control modulepossible
Internal fault in the control module that drives or monitors the ignition outputrare

How to diagnose

Read all stored and pending codes from every module, and note any other U codes or power supply codes that point to the same circuit
Record the freeze frame data and any status information, including battery voltage, ignition state and when the code set
Test battery condition and charging voltage, and check the terminals and main power and earth connections for tightness and corrosion
Check the relevant fuses and relays in the ignition and start circuit for condition and correct operation
Inspect wiring and connectors at the ignition switch or start button and the affected module for chafing, water ingress, corrosion or pin damage
Using the manufacturer wiring diagram, measure supply, earth and signal at the module connector with the ignition off, on and cranking
Check live data to see whether the ignition on/start status changes as expected when the switch is operated
Only after the wiring and power checks pass, consider testing or replacing the module, following the manufacturer procedure for the model

How to fix

Charge or replace a weak battery and clean and tighten terminals and earth points
Repair damaged wiring or connectors, or replace corroded terminals in the ignition on/start circuit
Replace a faulty ignition switch, start button or relay, and any blown fuse once the cause of the failure is found
Restore a poor earth connection at the affected module
Replace or repair the control module if it is confirmed faulty, and carry out any programming or adaptation the manufacturer requires
Clear the code after repair and confirm it does not return over a test drive and several start cycles

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 get worse. If it stalls, fails to start reliably or shows serious warnings, avoid driving it as it could leave you stranded or lose power at a dangerous moment.

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