Check Engine Light Blinking In Accessory Mode: Diagnosing Causes

Check Engine Light Blinking In Accessory Mode

Seeing your check engine light continuously blinking when your key is in the accessory position can be puzzling and concerning. While a steady check engine light indicates an existing fault, a blinking light is often more severe.

In this article, we’ll cover the most common reasons of why your check engine light may be blinking only when your key is on the accessory mode and how to diagnose the causes. We’ll discuss issues from ignition and fuel system problems to security system faults that can trigger this blinking when your engine isn’t running. 

Diagnosing why the light is blinking only in the accessory and nowhere else is vital to making the proper repairs and making sure your vehicle is on the safe side.

Faulty ignition coil

  • Bad ignition coils that cannot hold proper voltage when the engine is off will blink the check engine light in the accessory mode as a fault code. This is because the ECU detects the voltage leak from the coil.

Fuel injector issues

  • Leaking fuel injectors that continue injecting fuel with the engine off trigger the light to warn that the raw fuel enters the cylinders and exhaust.


Loose battery connection

  • A battery terminal that has become slightly loose or corroded can cause voltage fluctuations that appear as a fault and may blink the light in accessory mode.

Security system malfunction

  • Some import vehicles blink security lights when an aftermarket key or immobilizer issue is only on appearance in accessory power mode.

ECU power relay problems

  • Due to a faulty relay, the ECU may not power off correctly in accessory mode. This confuses sensors by triggering the blinking light.

Diesel glow plug circuit

  • If the glow plugs are inactive on diesel engines, it can trigger the ECU to blink the check engine light in accessory mode.
  • Check engine light blinking in accessory mode can signal a bad ignition coil, which cannot have a steady voltage. Use a multimeter and a load test coils to solve this issue. Also, replace any faulty ones if you found.
  • Use a noid light tester to check for leaking injectors that continues to open when the engine is off. Replace any stuck open injectors to overcome this issue.
  • Remove any corrosion and secure battery terminal connections to ensure a solid contact. This provides a stable voltage to avoid ECU confusion.
  • Attempt to start the vehicle with spare keys and check for stored security faults. Repair or replace immobilizer components if there are any.
  • Check that the voltage signal which goes to the ECU matches the ignition key position.
  • Scan and address any stored diagnostic trouble codes that are related to the diesel glow plug activation faults.

Frequently Asked Questions About Check Engine Light Blinking In Accessory Mode

A: No, it’s generally safe to drive temporarily if the light stops blinking with the running engine.

Q: Does the blinking light mean that my car won’t start, or is there an immobilizer issue?

A: Basically, blinking tied to anti-theft systems may prevent starting or indicate a lost key detection in accessory power mode. Key, ECU, and security system faults should have a repair to overcome this issue.

Q: How urgent is repairing an issue that causes the accessory-only check engine light blinking?

A: While not highly urgent, repairs should take place as soon as possible, as the fault likely indicates leaking fuel or oil conditions internally when the engine is off. These types of issues can worsen if left without any inspection.

Was this helpful?

Thanks for your feedback!

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *