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DTC codes / Volkswagen codes / P1624

P1624 · VolkswagenMIL Request Signal Active

P1624 on Volkswagen vehicles means the engine control module (ECM) has detected that the malfunction indicator lamp (MIL) request signal is active, which is a communication flag indicating another module or the ECM itself is requesting the check engine light to be turned on. The computer has seen a signal that says 'turn on the warning light' but the underlying fault that triggered the request is stored elsewhere, so P1624 is a messenger code rather than the root cause.

SystemPowertrain
Code typeVolkswagen specific
SeverityLow
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Check engine light (MIL) is illuminated on the dashboard, often with no other warning lamps.
  • Often no symptoms besides the warning light, and the vehicle may drive completely normally.
  • Intermittent illumination of the MIL that comes and goes with no pattern.
  • Possible rough running or reduced power if the underlying fault affects engine operation.
  • Other warning lights may appear if the request originates from a different control module.
  • The engine may enter limp mode in rare cases when the ECM cannot confirm the request source.

Common causes, most likely first

  1. A stored fault in another control module (such as the transmission, ABS, or airbag) that requests MIL illumination via the CAN bus.
  2. Faulty or corroded wiring in the CAN bus network between the ECM and other modules, causing a false MIL request signal.
  3. A failing ECM that incorrectly interprets or generates the MIL request signal internally.
  4. Low battery voltage or poor grounds that disrupt module communication and trigger spurious MIL requests.
  5. Aftermarket electronic accessories (alarms, audio, or piggyback tuners) interfering with the CAN bus signal.
  6. A software glitch in the ECM that requires a software update or adaptation reset.

How to diagnose and fix it

  1. Connect a Volkswagen-compatible scan tool and read all fault codes in every control module, not just the engine, to find the module that originated the MIL request.
  2. Check the battery voltage and condition, and verify clean, tight grounds at the engine and chassis, as low voltage is a common trigger.
  3. Inspect the CAN bus wiring and connectors at the ECM and other modules for corrosion, chafing, or loose pins.
  4. Disconnect any aftermarket electronic accessories and clear the code to see if the MIL request disappears.
  5. Perform a full vehicle scan and address any underlying fault codes in other modules before replacing the ECM.
  6. If no other faults are present, check for technical service bulletins (TSBs) or software updates for the ECM.
  7. As a last resort, replace and reprogram the ECM only after confirming all other possibilities are eliminated.

P1624 is rarely the real problem

  • P1624 is a secondary code that points to a MIL request from another module, so replacing the ECM without scanning all modules often leads to a misdiagnosis and a repeat failure.
  • A weak battery or poor ground connection can cause the ECM to misinterpret CAN bus messages and set P1624 even when all modules are healthy.
  • Aftermarket alarms or audio equipment tapped into the CAN bus can inject noise that mimics a MIL request signal, so always check for non-factory wiring first.
  • On some Volkswagen models, a software bug in the ECM causes a false P1624 that is fixed by a dealer software update rather than any hardware repair.
  • The code does not always mean the MIL circuit itself is faulty; the MIL request signal is a data message, not a direct wire to the bulb.

Can I keep driving with P1624?

You can generally continue driving if the only symptom is the warning light and the car runs normally, but avoid long trips or heavy loads until the underlying cause is found. If the engine runs poorly or other warning lights appear, have the vehicle checked promptly.

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 Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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