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P0383 – Glow Plug Control Module Control Circuit Low (OBD2)

P0383 means "Glow Plug Control Module Control Circuit Low". The voltage the control unit measures in the glow plug system circuit is below the permitted minimum. For a sensor this usually means the signal wire is shorted to ground or the reference voltage is missing; for an actuator, that its control wire is shorted to ground.

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P0383 quick summary

Fault codeP0383
MeaningGlow Plug Control Module Control Circuit Low
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityLow
Can I drive?Yes. In mild weather the engine usually starts normally; in cold weather expect hard starting and white smoke.
Repair cost€20 – €800

How diesel glow plugs work

Glow plugs heat the combustion chambers of a diesel engine so it starts reliably and runs smoothly when cold; these codes cover individual glow plugs, the control module and its circuits.

Each cylinder has a glow plug that heats up to around 1,000 °C within seconds. A glow plug control module (or relay on older engines) supplies them with current before and after starting. Many modern systems also keep the plugs on for several minutes after a cold start (after-glow) to reduce smoke and noise.

The control module monitors each plug's current. It reports faults for individual cylinders (P0671–P0682), the overall circuit (P0380, P0382), the indicator lamp and the communication between module and engine control unit (P0683, P0684).

One failed glow plug often goes unnoticed in mild weather but causes hard starting, white smoke and rough running in winter. Glow plugs can seize in the cylinder head, so removal needs care.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 16767 (P0383). Both numbers mean the same fault.

Symptoms of P0383

  • Hard starting in cold weather
  • White smoke and rough running after a cold start
  • Glow plug lamp flashing or Check Engine light
  • Knocking noise when cold
  • Sometimes no symptoms in mild weather

Most common causes of P0383 (most likely first)

Mechanic's Pro Tip

Never force a seized glow plug out of a cold engine. Warm the engine, soak the thread, and loosen it slowly back and forth. A snapped glow plug often means removing the cylinder head.

  1. 1.Signal or control wire shorted to ground

    Most likely

    Look for chafed insulation where the harness touches the engine, exhaust brackets or body edges.

  2. 2.Missing 5 V reference or supply voltage

    An open reference wire or a shorted sensor elsewhere on the same reference circuit can pull it down.

  3. 3.Internal short in the glow plug system

  4. 4.Burnt-out glow plug(s)

  5. 5.Faulty glow plug control module or relay

  6. 6.Damaged wiring or loose terminal nut on the glow plug

  7. 7.Blown fuse or fusible link

Step-by-step diagnostic guide

  1. 1

    Read codes

    Read the engine and glow plug module codes to find which cylinder or circuit is affected.

  2. 2

    Measure the signal voltage

    With the ignition on and the glow plug system plugged in, back-probe the signal wire. Then unplug it and check the reference/supply and ground wires separately.

    Multimeter: Signal near 0 V = short to ground or no reference. Reference wire: about 5 V with ignition on. Signal wire to ground with connector unplugged: no continuity.

  3. 3

    Measure the glow plug

    Disconnect the plug's terminal and measure its resistance to ground or its current draw.

    Multimeter: Most glow plugs read below about 1–2 Ω; 'OL' means burnt out. Current draw: often around 8–15 A per plug when hot.

  4. 4

    Check supply from the module

    Check that the module supplies voltage to each plug during the glow phase.

  5. 5

    Check fuse and module

    Check the main fuse and the module's supply, ground and control signal.

  6. 6

    Replace carefully

    Warm the engine, use penetrating oil and the correct torque. Replace all plugs if they are old.

Frequently asked questions

Can I keep driving with P0383?

Yes. In mild weather the engine usually starts normally; in cold weather expect hard starting and white smoke.

How much does it cost to fix P0383?

Typical repair costs are 20 € – 800 €, depending on the cause and the vehicle. The most common fixes are: signal or control wire shorted to ground; missing 5 V reference or supply voltage; internal short in the glow plug system. Always confirm the cause with the tests above before buying parts.

Should I replace all glow plugs at once?

If they are old, yes – the others usually fail soon after and the work is similar. Replace them only if they come out without excessive force.

Can a bad glow plug damage the engine?

Not directly, but very hard starting puts extra strain on the starter and battery, and a broken glow plug tip in the cylinder can cause serious damage.

What is the difference between P0383 and similar codes?

P0383 belongs to a group of codes for the same component that differ in the type or location of the fault: P0380 – Glow Plug/Heater Circuit A Malfunction; P0381 – Glow Plug/Heater Indicator Circuit Malfunction; P0382 – Glow Plug/Heater Circuit B Malfunction; P0384 – Glow Plug Control Module Control Circuit High; P0670 – Glow Plug Module Control Circuit; P0671 – Cylinder 1 Glow Plug Circuit. The tests on this page apply to the whole group; the type of fault tells you where to start.

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.