Can I still drive with P0672?

Yes, especially in mild weather, since one weak glow plug mainly affects cold starting. It is not a safety fault, but cold starts will get harder as winter approaches, so do not leave it indefinitely.

Will one failed plug stop the engine starting?

Rarely on its own in mild conditions. In hard frost, though, a single dead plug can make a cold start very difficult and produce a lot of white smoke until the engine warms.

Should I change all four glow plugs?

On a high-mileage diesel it is sensible. If cylinder 2 has worn out, the others are usually not far behind, and doing them together saves repeating an awkward job.

Do glow plugs need a special tool?

A dedicated glow plug socket helps and a thread chaser is useful. The main risk is seizing, so the right socket, penetrating oil and patience matter more than anything fancy.

How much should P0672 cost to fix?

A single plug is often £8–£30, with a full set fitted around £80–£200 at an independent garage. Wiring or connector repairs can be cheaper if that turns out to be the cause.

Could P0672 trigger a misfire code too?

It can. A dead glow plug gives poor cold combustion on that cylinder, so a cold-start misfire code sometimes appears alongside it until the engine reaches temperature.

P0672 - Glow Plug Circuit - Cylinder 2

What Is P0672?

P0672 tells you the glow plug control module has flagged a circuit fault on cylinder 2. Modern diesels monitor each glow plug separately, measuring the current each one draws during preheat, so the module can pinpoint which plug or which length of wiring has gone wrong.

On cylinder 2 the fault is most often the glow plug element wearing out after years of heat cycling, but the connector and the short branch of wiring feeding it are common culprits too. Glow plugs matter most in cold weather, so P0672 is worth fixing before the temperature drops.

Common Symptoms

Glow plug warning light on or flashing
Hard starting when cold, easier when warm
Puff of white smoke on a cold start
Rough idle for the first minute from cold
Engine management light
Slightly down on power until warm

Common Causes

Worn cylinder 2 glow plug - the heating element has aged and gone open or high-resistance, the usual cause.

Wiring fault - an open or high resistance in the feed between the module and the cylinder 2 plug.

Corroded connector - the spade or plug terminal on cylinder 2 oxidised and losing contact.

Cracked plug tip - a split element causing an internal short or open.

Module output fault - the control module's drive for cylinder 2 has failed, less common.

Loose terminal nut - the small nut on the plug working loose and arcing.

How to Diagnose P0672

Read Per-Cylinder Data

A capable scanner can show each glow plug's status. Confirm the module is reporting the fault specifically on cylinder 2 before you start removing anything.

Resistance Test the Plug

Disconnect cylinder 2 and measure from the plug terminal to the engine block. A good plug reads about 0.5–2 ohms; infinity means the element has failed open.

Check the Feed Wire

With the plug unplugged, test continuity from the connector back to the module output for cylinder 2. No continuity means a broken wire, often where the loom passes the hot exhaust.

Inspect the Connector and Nut

Look at the terminal for burning or corrosion and check the retaining nut is tight. High-current connections burn if they loosen, which can mimic a plug fault.

Compare All Four Plugs

If you have the access, ohm every plug. Glow plugs tend to fail in groups on a high-mileage engine, so it is worth knowing the condition of the rest.

Replace the Plug

Once confirmed, soak the thread in penetrating oil, remove with the correct glow plug socket, and fit the new plug to the maker's torque, usually 8–15 Nm. Clear the code and test a cold start.

Seized Plug RiskGlow plugs can seize solidly in an alloy head after years of heat. Only remove them from a cold engine, never force a tight one, and apply penetrating oil generously - a sheared plug needs specialist extraction and turns a small job into a big one.

Verdict

Test the cylinder 2 glow plug's resistance first - a worn-out plug is by far the most common cause of P0672. If the plug is good, check the connector and the feed wire back to the module before suspecting the module itself.

Want the full picture? The OBD Fault Code Plain English Guide (PDF) covers the most common UK fault codes in one plain-English download.