P0673: Cylinder 3 Glow Plug Circuit

What it means

An electrical fault is present in the glow plug circuit for cylinder 3. The glow plug control module cannot drive this plug correctly — open circuit, short, or out-of-range resistance — so cylinder 3 is not pre-heated. On a cold start this causes hard starting, white smoke, and a misfire-like rough run until the engine warms. Causes: a failed glow plug, a broken supply lead to that plug, corrosion at the plug connector, or a faulty module output for cylinder 3.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The glow plug in cylinder 3 helps that cylinder ignite diesel fuel when the engine is cold, and the glow plug control module switches power to it. P0673 sets when the module detects an electrical problem in the cylinder 3 glow plug circuit, such as an open, short, or out-of-range resistance. It refers specifically to cylinder 3’s circuit.

Common causes

Most likely first.

1. Failed cylinder 3 glow plug
2. Open or shorted wiring to the plug
3. Corroded or loose connector
4. Glow plug control module output fault

Symptoms

• Glow plug warning light on (often orange coil symbol)
• Hard cold start or no start in cold weather
• White smoke from exhaust during warm-up

How to diagnose it

1. Record freeze-frame data and check for companion glow-plug codes to determine whether the fault is isolated to cylinder 3.
2. Use service information to locate cylinder 3, then inspect its glow plug connector and lead for corrosion, a loose fit, chafing, or heat damage.
3. Following the manufacturer’s safety procedure, isolate the circuit and measure the cylinder 3 glow plug against the manufacturer’s specification.
4. Check the cylinder 3 lead and connector for an open circuit or short using the vehicle wiring diagram.
5. If the plug and lead pass, test the module output assigned to cylinder 3 with the specified scan-tool or electrical test.
6. After repair, clear the code and check for its return during a cold start.

Common fixes

• Clean and secure the cylinder 3 glow plug connection.
• Repair damaged wiring or a poor connector contact in the cylinder 3 branch.
• Replace the cylinder 3 glow plug if it fails testing.
• Repair or replace the cylinder 3 output in the glow plug module if the plug circuit is sound.

Can I keep driving?

If the engine runs normally after warming up, limited driving may be possible, but cold starts can cause rough running, white smoke, or extended cranking. Avoid repeated start attempts and repair it promptly if the engine runs unevenly after starting.