P0672 on the 6.6L Duramax LB7 is a glow plug cylinder 2 circuit fault. The Duramax uses glow plugs to preheat each cylinder for cold starts, and the glow plug control module monitors each plug's current draw. P0672 sets when the module sees the cylinder 2 glow plug circuit outside its expected range, indicating an open plug, a shorted plug, or a wiring fault to that cylinder.
A per-cylinder glow plug code is helpful because it isolates the fault to one plug and its feed. On the Duramax the glow plugs thread into the cylinder heads and are fed through wiring routed near the valve covers. P0672 usually means the cylinder 2 plug has failed open or the wiring to it is damaged, both of which are targeted repairs once you confirm the plug's resistance and its circuit.
What P0672 means
The glow plug control module energizes each plug and monitors current. P0672 sets when the cylinder 2 circuit reads outside the acceptable range, pointing to an open glow plug, a shorted plug, or an open or short in the wiring to cylinder 2. It is a cylinder-specific circuit code that isolates the fault to that plug and feed.
Common causes
- Open or burned-out cylinder 2 glow plug
- Shorted glow plug drawing excess current
- Damaged or chafed wiring to cylinder 2
- Corroded or loose glow plug terminal
- Poor connection at the glow plug feed
Symptoms
- Hard cold starting and longer cranking
- White smoke and a rough cold idle
- Check engine light with P0672 stored
- One cylinder slow to contribute on a cold start
- Normal running once warm
How to diagnose it
Locate the cylinder 2 glow plug and measure its resistance; a healthy plug reads low, an open plug reads very high. Inspect the terminal and wiring to cylinder 2 for corrosion, chafing, and a secure connection. Check the feed from the glow plug control module for an open or a short. Compare cylinder 2 against a known-good cylinder to confirm the fault is isolated rather than a module-wide problem affecting several plugs.
How to fix it
Replace the cylinder 2 glow plug if it reads open or shorted, and repair damaged wiring or a corroded terminal. If the plug and wiring test good but the fault returns, test the glow plug control module. After the repair, clear the code, confirm the glow plug circuits pass, and verify a clean cold start with no white smoke. For glow plugs, wiring, and glow plug control modules for your LB7 Duramax, contact sales@coredieselparts.com.
Frequently asked questions
Will P0672 keep my LB7 from starting?
Usually not by itself, but one dead glow plug makes cold starts harder and produces white smoke and rough running until the engine warms. Fix it before cold weather.
How do I know if the glow plug is bad?
Measure its resistance. A good glow plug reads a low resistance value, while an open or burned-out plug reads very high or infinite, which matches the P0672 circuit fault.
Can bad wiring set P0672 with a good plug?
Yes. A chafed or corroded feed to cylinder 2 can set the code even if the plug is fine. Confirm the wiring and terminal before replacing the glow plug.
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