When you see P0673 pop up, what you’re really being told is that there’s an open circuit in the glow plug circuit for cylinder number 3. From my time with diesel engines, this is the PCM’s way of letting you know that the glow plug in cylinder 3 isn’t heating up properly. Those glow plugs? They’re absolutely vital for diesel engines, especially when you’re trying to get things fired up on a frosty morning. They preheat the air in the cylinder so the engine can turn over smoothly. The PCM keeps a close eye on both the temperature and current going to each glow plug, and if it notices that the cylinder 3 glow plug isn’t drawing the right current-or none at all-it throws this code. In short, this whole setup is about making sure your diesel actually starts, even when there’s frost on your breath.
DTC P0673
5870
5 minutes of readingCauses of dtc P0673
Speaking as someone who’s chased a lot of these codes, the top culprit for P0673 is usually a worn-out glow plug. They’re like spark plugs in gas engines-eventually, they just give up. But don’t stop there. I’ve run into plenty of cases where the real problem was a busted wire, a corroded connector, or even a loose plug that someone forgot to snap in properly. On occasion, the glow plug control module will call it quits and stop sending juice to the plug. And, not to be overlooked, sometimes the wiring harness itself develops an open or a short. Here’s the typical list I see in the shop:
- Burned out glow plug in cylinder 3
- Failure of the glow plug control module
- Corroded or damaged connectors
- Open or shorted wiring in the glow plug circuit
- Glow plug harness issues
Here’s a pro-tip from the garage: always check the simple stuff before blaming the control module. Saves a lot of headaches.
Symptoms of P0673 code
If your rig’s throwing a P0673, the check engine light will be staring you down. Most folks also notice it’s a real bear to start the engine, especially if it’s cold out. Watch your dash-sometimes the glow plug light hangs around longer than usual, or just won’t go out. In freezing weather, you might find yourself cranking and cranking, or the truck just refuses to start. Don’t brush these signs off. Forcing a diesel to start without proper glow plug action can really mess things up in a hurry.
Diagnosis and P0673 engine code
When I’m tracking down a P0673, here’s my go-to process:
- Battery first-make sure it’s healthy. Low voltage can throw the whole glow plug system off.
- Next up, I get in there and eyeball the wiring and connectors at cylinder 3. Look for broken wires, greenish corrosion, or anything that looks loose. If you’ve got a helper, have them wiggle the harness while you watch for any changes.
- With a multimeter, I check for voltage at the glow plug right after turning the key to ‘on’. No voltage? That means the issue is upstream-could be the control module or the wiring before it.
- Getting voltage? Then I pull the plug and check its resistance. A healthy glow plug will usually read between 0.5 and 2 ohms. If it’s open or reading infinity, it’s toast and needs replacing.
- If the plug tests out, I move on to checking the control module and the rest of the circuit. A good scan tool with live data really helps here-you can spot if the module isn’t sending power to cylinder 3.
One thing I always do: check all the glow plugs, not just the one the code is pointing at. If one’s failed, odds are the others aren’t far behind.
Common Mistakes with obd code P0673
A classic mistake I see is folks swapping out the glow plug without even glancing at the wiring or control module. Some skip the resistance test and just start throwing parts at it. That’s a quick way to waste both time and money. Overlooking little things-like corrosion or a loose connector-can create big headaches. Always take a minute to double-check the basics before moving on to pricier components.
Seriousness of obd2 code P0673
I can’t stress this enough-don’t ignore a P0673. If you let it slide, you’re asking for hard starts, especially when the mercury drops. Keep forcing the engine and you might end up draining your battery or burning out the starter. Worst-case scenario? Unburned fuel washes down your cylinder walls, and that’s a recipe for expensive engine damage. If you count on your diesel every day, or you live where winter means business, get this sorted before you end up stranded.
Repair solutions for P0673 trouble code
Nine times out of ten, the fix is a new glow plug for cylinder 3. But if you spot damaged wiring or a crusty connector, repair or replace that too. If the glow plug control module isn’t sending power, it’s got to go. And don’t forget-after you fix it, clear the code and make sure everything’s working right before calling it done. My top recommendations:
- Replace the bad glow plug (stick with OEM for reliability)
- Repair or swap out any damaged wiring or connectors
- Replace the control module if it’s not delivering power
- Double-check all related circuits to make sure the fix sticks
Conclusion
Bottom line: P0673 means your cylinder 3 glow plug circuit isn’t doing its job, and that’s going to make cold starts a real pain. It’s essential to jump on the diagnosis-start with the glow plug itself and work your way through the wiring and control module if you have to. Letting this go is just asking for trouble, from being stranded to doing serious engine damage. The right way to handle it? Test everything methodically, replace what’s bad, and make sure the whole system’s ready before you trust it out on the road.
