Glow Plug #4 Circuit Failure
The P0674 code indicates a malfunction in the glow plug circuit for cylinder #4. Glow plugs are used in diesel engines to preheat the combustion chambers for cold starts. This code is set when the powertrain control module (PCM) detects an open or short circuit in the glow plug #4 circuit, or when the glow plug resistance is out of specification. Common causes include a faulty glow plug, damaged wiring or connector, or a failed glow plug control module.
01. Most Common Causes
- Faulty glow plug #4
- Open or shorted wiring in glow plug #4 circuit
- Damaged connector at glow plug #4
- Failed glow plug control module
02. Symptoms You Will Notice
- Hard starting, especially in cold weather
- Rough idle or misfire on cylinder #4
- Check Engine Light illuminated
- Excessive white smoke on startup
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0674 and check for other codes.
Step 2: Visually inspect glow plug #4 wiring and connector for damage or corrosion.
Step 3: Measure resistance of glow plug #4; compare to specification (typically 0.5-2 ohms).
Step 4: Test voltage at glow plug #4 connector with key on; should see battery voltage for a few seconds.
Step 5: If wiring and plug are good, test glow plug control module output for cylinder #4.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances in mild weather, but starting will be difficult in cold conditions. Continued driving may cause unburned fuel to damage the catalytic converter.
How much does it cost to fix?▼
Replacing a single glow plug costs $50-$150 including parts and labor. If the control module or wiring needs repair, costs can be higher.