Meaning of P0674 Duramax: Reasons & Solutions

What is the P0674 Duramax error code? This powertrain code appears for some issues with the cylinder 4 glow plug. Several causes are responsible for this error code. Solutions are similar for all year models. Only some specific repair steps can be different.

When you are in freezing weather, your vehicle is dependent on this glow plug. Without the help of a cylinder 4 glow plug, you cannot cold start your diesel engine. Any glow plug issues prevent the system from heating the cylinder head of the cold engine and letting it start.

What are the reasons, how do recognize the issues, and what solutions? Everything you need to know about this code is here. Let’s enter deep and find out the fact.

Solutions to Specific Causes for P0674 Duramax

Defective glow plugsHard to start Hesitation in acceleration
Shorted glow plug circuitThe engine will miss the run even in warm weather Fail to cold start
Damaged wires or connectorsThe engine cannot be heated properly Black smoke may appear
Damaged glow plug control moduleWhite smoke may appear Failure in cold start

Defective Cylinder 4 Glow Plugs

The primary cause of the defect in the glow plug cylinder is excessive heat production and the reaching of high voltage to the glow plug. The high voltage problem is caused for the issues with the controller.

If there is a fault in only one glow plug in cylinder 4, the system will show minimal symptoms, and only the check engine light will show out. The vehicle can perform the cold start if only one glow plug is faulty. If more than one glow plug becomes defective, it will show a signal like 2012 Duramax P0674. Then the engine will get a complex start symptom.


To check if the glow plug is faulty, you have to run a digital volt ohmmeter test (DVOM).

  • First, scan the system in the computer by the OBD code scanner. Then reset the computer after erasing the error code. Now check if the P0674 code appears again run the test.
  • Disconnect the connector of the glow plug. Then take the DVOM on ohms mode.
  • Connect the meter’s red lead to the terminal of the glow plug.
  • Connect the black lead to the good ground.
  • Now check the meter reading. The proper meter reading range is from 0.5 ohms to 2.0 ohms. The glow plug is okay if you find the reading between this range. Otherwise, you have to replace the defective plug.

Disconnected or Shorted Glow Plug Circuit

If the glow plug circuit is shorted or disconnected, it can shut down the entire bank of cylinder 4. So, it is a sensitive issue and needs to solve immediately after getting the symptom or P0674 6.6 Duramax code.

The primary symptom for the shorted or disconnected circuit is a break in continuity in the control module of the glow plug. The engine may miss the run-in colder weather. The machine will not get enough power to heat up.


If you find the open glow plug circuit, you have to reconnect it and check if it is okay now. If you get the P0674 Chevy Duramax code again, you must replace the entire circuit.

Damaged Wiring and Connector

If the wiring and the connector are damaged, the engine will not get sufficient power and cannot be heated for a cold start. Even in warm weather, the engine may hesitate to accelerate properly. When most connectors are disconnected, it will get a hard start situation.


At first, you have to check the resistance in the glow plug wire to the relay buss bar, which is situated at the valve cover. There is a large gauge wire connected to the buss bar, where all the glow plugs’ cables are connected.

Also Read: P0087 Duramax Fixing with Reasons Explained

Look for the disconnected wires, loose connections, cracks, etc. Anything problems should be solved accordingly.

Defective Control Module of the Glow Plug

If the control module of the glow plug in cylinder 4 is defective, it will cause the diesel to be leaked into the exhaust for burning. Then white exhaust smoke will appear. Then the engine will face a hard start situation even in warm weather. In the colder weather engine will fail. So, the P0674 GMC Duramax will show, and a no-preheat period will arrive.


  • To check the control module, connect a 12-volt testing light to the positive side of the battery terminal.
  • Now disconnect the glow plugs by disconnecting the wires.
  • Attach the test light probe to the glow plug terminal.
  • The glow plug control module is okay if the light is on. Otherwise, you have to replace it.

Thus, you have to check one glow plug control module at once.

After testing every part of the glow plugs, connect the dedicated code scanner under the dash and turn the plugs on when the engine is off. Delete the P0674 LMM Duramax code. Then check the engine. If the fault code does not reappear, then the glow plugs are suitable.

This Video Will Help You Too!

Frequently Asked Questions (FAQs)

What is code P0674 mean?

P0674 Duramax code is a powertrain control module trouble code that shows up if there are any issues with the cylinder 4 glow plug circuit. This glow plug circuit is responsible for heating the engine for a cold start in colder weather. If there is any problem with these plugs and the system, it can cause a problem with the engine even in warm weather.

How do I fix code P0674?

If the glow plugs in cylinder 4 are faulty, there are some symptoms like white smoke, discontinuity in engine run, and hesitation in the engine’s acceleration. When finding the P0674 Duramax LBZ, check and test the glow plugs using the ohmmeter. If you find faulty wiring, connectors, control modules, or glow plugs, replace them.

Where is the glow plug module on a Duramax?

The glow plug module on a Duramax is situated on the driver side under the firewall. It is at the turbocharger point. It is attached directly to the engine to collect the necessary information.


There are specific trouble codes for vehicle engine and parts performances and situations. These trouble codes provide signals to alert the driver of particular symptoms. P0674 Duramax error code is linked to the cylinder 4 glow plugs. Since glow plugs are for the cold start in colder weather, the problem with these plugs can show issues with the engine even in warm weather.

When you find the signal for this code, you should not waste time. The wise actions are to check the system immediately and find the issue. You can seek help from an expert mechanic.

You Can Also Read:

D Conroy

Meet our senior writer and content manager of Automasterx. He has worked in several mechanical garages and mastered different vehicle diagnoses and parts repair. He never stops until finding out the ultimate solutions for any vehicle fault code. However, ensuring the only solid solutions for each vehicle malfunction is his core part of the duty, alongside analyzing fault codes and signals.

Similar Posts