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DTC codes / U30xx · Network wiring and bus faults / U302D

U302DIgnition Output On/Start

U302D is a generic network communication code indicating that a control module has detected a fault on the ignition output-on/start signal circuit, which is used to wake up or enable other modules when the ignition is turned on or the engine is started. The computer monitors the voltage or message on this circuit and sets the code when the expected signal is missing, delayed, or out of range.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaNetwork wiring and bus faults

Symptoms you may notice

  • The engine may not start or may crank without firing, especially in vehicles with push-button start.
  • Multiple warning lights on the dashboard, such as ABS, airbag, or traction control, may illuminate simultaneously.
  • The ignition may not turn on certain accessories or may require multiple presses of the start button.
  • Intermittent no-start conditions where the vehicle eventually starts after several attempts.
  • Often no symptoms besides the warning light, with the vehicle operating normally.
  • Other modules may log communication codes or fail to respond to scan tool requests.

Common causes, most likely first

  1. A weak or failing vehicle battery that cannot maintain stable voltage during ignition-on or cranking events.
  2. Corroded, loose, or damaged wiring or connectors on the ignition switch or start signal circuit.
  3. A faulty ignition switch or start button that does not properly close the circuit.
  4. A defective body control module (BCM) or gateway module that fails to process or transmit the ignition-on/start signal.
  5. A blown fuse or relay in the ignition or start signal power path.
  6. Water intrusion or physical damage to the wiring harness affecting the ignition signal circuit.
  7. Software or configuration errors in a module that handles the ignition status message.

How to diagnose and fix it

  1. Perform a battery and charging system test to rule out low voltage as the root cause.
  2. Use a scan tool to read all modules for related codes and check live data for ignition switch status parameters.
  3. Visually inspect the ignition switch, start button, and associated connectors for corrosion, looseness, or damage.
  4. Check fuses and relays related to the ignition and start circuits, replacing any that are blown or faulty.
  5. Measure voltage and continuity on the ignition output-on/start signal circuit at the module connectors to verify signal integrity.
  6. If the signal is missing at a module, test the ignition switch or start button with a multimeter and replace if defective.
  7. For intermittent faults, perform wiggle tests on harnesses and connectors while monitoring live data to locate the fault.

Ignition Signal Faults That Fool Technicians

  • A weak battery is the most common cause of U302D, yet many technicians replace modules before checking voltage during cranking.
  • The code can be set by a module that is not the ignition switch itself, such as a body control module or gateway, so always check all modules for communication errors.
  • In some vehicles, aftermarket accessories wired into the ignition circuit can back-feed voltage and cause the module to see an invalid ignition-on/start signal.
  • U302D may appear after jump-starting a vehicle incorrectly, which can spike the ignition circuit and damage a module or blow a fuse.
  • A faulty ground connection for the module that monitors the ignition signal can mimic a defective ignition switch, so ground integrity must be verified.

Can I keep driving with U302D?

If the vehicle starts and runs normally, you can drive it to a repair shop, but avoid turning the ignition off until you arrive because a no-start condition may occur. If the engine will not start or stalls intermittently, do not drive and have the vehicle towed to prevent being stranded.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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