When you see a P0674 code, it means your engine control module has picked up on a problem with the glow plug circuit in cylinder number 4. Let me put it in real-world terms: the computer that runs your truck or car (the PCM) is telling you that the electrical path that heats up glow plug number 4 isn’t behaving the way it should. If you’ve worked on diesel engines like I have, you know those glow plugs are critical-especially when temperatures drop. Their job? Preheat the air in the combustion chamber so your diesel fires up smoothly. If one of them isn’t working, you’ll fight with hard starts or a rough idle until things warm up. In the case of P0674, you’re looking at an open or faulty circuit just for cylinder 4’s glow plug, but don’t rule out issues with the wiring, connectors, or even the glow plug control module. All three can throw this code.
DTC P0674
4924
6 minutes of readingCauses of P0674 trouble code
From my time under the hood, I can tell you that a failed glow plug in cylinder 4 is the most common culprit when p0674 shows up. But don’t get tunnel vision-there’s more to it than just a bad plug. Here’s what I see most in the shop:
- Glow plug in cylinder 4 has failed-the internal heating element is burnt out or broken.
- Wiring or connectors have issues: frayed wires, loose fits, or corrosion are all too common.
- The glow plug control module itself has failed and isn’t sending power where it should.
It’s usually one of these three, but take a methodical approach and check each one before you start swapping parts. Chasing your tail gets expensive fast.
Symptoms related to obd2 code P0674
If you’ve got this code, you’ll probably notice more than just the check engine light glaring at you. Hard starting-especially on those frosty mornings-is a dead giveaway. Sometimes you’ll crank and crank, and the engine just doesn’t want to catch. If it’s cold enough, it might not start at all. And once it does fire up, you may feel it sputter or run a little rough until things get up to temperature. Lack of power right after startup isn’t uncommon, either. All classic signs that the glow plug system isn’t up to par.
Diagnosis steps for P0674
When I tackle an obd p0674 code, I always stick to a simple rule: start with the basics. Don’t overcomplicate things at the outset.
- Fire up your OBD-II scanner and confirm the code-double-check for any buddy codes that might give you more clues.
- Pop the hood and eyeball the wiring and connectors leading to cylinder 4’s glow plug. Look for visible wear, broken wires, or corroded pins. Don’t be afraid to wiggle the connector; sometimes a poor contact only shows itself when disturbed.
- If everything looks tidy, grab a multimeter and check the resistance of the glow plug itself. Compare what you find to the specs in your manual-if it’s way off, there’s your problem.
- If the plug tests good, trace the wiring back to the control module and check for continuity. I’ve seen plenty of broken or shorted wires cause headaches here.
- If you’re still coming up empty, it’s time to test the glow plug control module. This is where you want to follow the service manual closely-guesswork here leads to wasted time and money.
Common Mistakes when resolving P0674 engine code
A classic mistake I see all the time? Folks rush into replacing the glow plug without checking the wiring or the control module. That’s an easy way to throw money away if the real problem is a corroded connector or a broken wire. And here’s something a lot of people overlook: always test the resistance of your new glow plug before dropping it in. Believe it or not, I’ve seen brand new plugs that were dead out of the box. Don’t gloss over the connectors, either-if you’re in a damp or salty area, corrosion is almost a given. Skipping these checks almost always means you’ll be back under the hood sooner than you’d like.
Seriousness of obd code P0674
If you’re tempted to ignore this one, don’t. Especially if you count on your diesel to start up every morning in cold conditions. A faulty glow plug circuit can leave you stranded with a no-start when you least expect it, and repeated hard starts can chew up your starter and drain your battery in a hurry. I’ve seen neglected glow plug issues lead to unburned fuel in the exhaust-bad news for your DPF, catalytic converter, or injectors. Long story short: let this slide, and you’re asking for bigger (and pricier) problems down the road.
Repair options for P0674 code
Once you’ve tracked down the root cause, here’s my usual go-to fix for a p0674:
- Swap out the glow plug in cylinder 4 if it’s out of spec or not firing up.
- Patch up or replace any bad wiring or sketchy connectors in the circuit.
- Clean up any corroded connections and give ’em a dab of dielectric grease for future protection.
- If the control module’s toast, follow the service manual and replace it by the book.
Conclusion
Bottom line, P0674 means the glow plug circuit for cylinder 4 isn’t up to snuff. Nine times out of ten, it’s a bad plug, but faulty wiring or a busted control module can be the real troublemakers. Don’t ignore it-hard starts and potential engine or exhaust damage are real possibilities. Start with the simple checks, work your way up, and always verify your repair before you button things up. That’s how you keep your diesel firing up strong and running like it should.
