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16684 – Random/Multiple Cylinder Misfire Detected (Older VAG 5-Digit Code) (VAG 1.8 20V Turbo)

On VAG vehicles, fault code 16684 (OBD2: P0300) means "Random/Multiple Cylinder Misfire Detected (Older VAG 5-Digit Code)". It is common on 1.8 20V Turbo (AUM, AUQ, ARZ, BAM), 1.6 8V / 16V, 2.0 8V, 1.4 16V, 2.8 / 2.9 VR6 engines. Below are the real-world causes, step-by-step tests and OEM part numbers.

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16684 quick summary

Fault code16684
OBD2 codeP0300
MeaningRandom/Multiple Cylinder Misfire Detected (Older VAG 5-Digit Code)
SystemPowertrain (Engine & Transmission)
VehiclesVAG (VW, Audi, Škoda, Seat)
Common on1.8 20V Turbo (AUM, AUQ, ARZ, BAM), 1.6 8V / 16V, 2.0 8V, 1.4 16V, 2.8 / 2.9 VR6
SeverityHigh
Can I drive?Only gently. If the engine shakes heavily or the Check Engine light flashes, stop – unburnt fuel overheats the catalytic converter.
Repair cost€20 – €600

Symptoms of 16684

  • Engine shakes or stutters, especially under load
  • Check Engine light on or flashing
  • Rough idle, sometimes only when cold
  • Loss of power and higher fuel consumption
  • Often stored together with 16685–16690 (misfire cylinder 1–6)

Most common causes of 16684 (most likely first)

Mechanic's Pro Tip

16684 is simply P0300 in the older VAG 5-digit format: 16384 + 300. On these engines the order of suspects is spark plugs, ignition coils (the 1.8T coil packs are notorious), then vacuum leaks from cracked breather hoses. Watch the misfire counters per cylinder in measuring blocks 015/016 with VCDS – then swap a coil with a neighbouring cylinder and see whether the misfire moves.

  1. 1.Worn spark plugs or wrong plug gap

    Most likely

  2. 2.Faulty ignition coil(s) or ignition leads

  3. 3.Vacuum leak – cracked breather (PCV) or vacuum hoses

  4. 4.Clogged or leaking injector

  5. 5.Low compression (valves, piston rings, head gasket)

Step-by-step diagnostic guide

  1. 1

    Read all codes in Engine (01) with VCDS; note which cylinder-specific codes (16685–16690) are stored.

  2. 2

    Watch the misfire counters per cylinder in measuring blocks 014–016 at idle and on a test drive.

  3. 3

    Inspect the spark plugs and replace them if they are worn or the interval is due.

  4. 4

    Swap the ignition coil of the affected cylinder with another cylinder and check whether the misfire moves.

  5. 5

    Check for vacuum leaks (smoke test) and, if the misfire stays with one cylinder, do a compression test.

Frequently asked questions

Is 16684 the same as P0300?

Yes. Older VAG control units show OBD2 codes as 5-digit numbers: 16384 plus the P-code number. 16684 = P0300, 16685 = P0301, and so on.

How much does it cost to fix 16684?

A set of spark plugs costs a few dozen euros, an ignition coil about 20–80 €. Vacuum hoses are cheap. Injector or compression problems cost more – from a few hundred euros.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.