What Is P0678 Code On 6.0L Powerstroke: How To Fix?

Ford 6.0L Powerstroke’s PCM generates several trouble codes to notify the user about the inner situation. The P0678 is one of them & it’s related to the glow plug section. 

If you have the error code P0678 & want to know about it in-depth, this article is for you. In this article, I’ll be discussing symptoms to troubleshooting methods for you to try & succeed. 

What Is P0678 Code On 6.0L Powerstroke

What Does P0678 Code Means On 6.0L Powerstroke? 

P0678 is one of the Diagnostic Trouble Codes (DTCs) of the Ford 6.0L Powerstroke. By definition, the P0678 refers to the Cylinder 8 Glow Plug Circuit.

Diesel engines come with eight cylinders & each of them have one glow plug on the top. The main objective of the glow plug is to heat the fuel to make the engine ignite properly. 

Eight of the glow plugs need to be working fine to start the engine in time. If any of them malfunction, your vehicle will suffer at the start – especially in the cold environment. 

The Powertrain Control Module (PCM) monitors each & every glow plug. When the PCM notices any unexpected activities from the #8 Glow plug, it generates the DTC P0678. 

Symptoms Of Getting The P0678 Code On A 6.0L Powerstroke

The P0678 comes with some visible symptoms for you to identify the code. Here are the most common symptoms of the error code P0678:

  1. The Engine Will Take Longer Time To Start
  2. Lack Of Power During Start-Up
  3. Sometimes Engine May Miss Start In The Colder Temperature
  4. Visible Accelerating Issue 
  5. The Preheat Light Won’t Go Off, Means No Pre-Heat Period
  6. Engine Light On 

Don’t be too happy if you’re not getting five of these symptoms. Expect to have the error code P0678 if you’re getting two or more symptoms mentioned above. 

The Causing Factors Of The Error Code P0678

The error code P0678 doesn’t come out of the blue. Some certain reasons/causes result in the DTC P0678. For your clearer understanding, here are the most common causing factors of the error code P0678:

  1. Defective/Damaged 8no. Cylinder Glow Plugs
  2. Defective/Damaged Glow Plug Relays or Timers
  3. Worn Out Wirings & Damaged Connectors
  4. Glow Plug Circuit is Open Or Shorted 
  5. Defective/Damaged Glow Plug Control Module 

Though all of these causes are glow plug-centric, don’t ignore them. To know how serious this DTC could be, follow the next segment. 

How Serious Is Code P0678 On 6.0L Powerstroke?

The glow plug gives the initial push to the engine to start even in a colder atmosphere. When one or some of them become faulty, the vehicle will still be drivable.

However, you shouldn’t drive your vehicle having a glow plug issue or DTC P0678 as you might face several problems. For instance, you’ll have a hard start & sometimes your engine might even refuse to start. 

How to Solve P0678 Error Code On 6.0L Powerstroke?

This problem is mostly about the glow plug & that’s why you can expect to have glow plug replacement in this solve part. To know this & other methods thoroughly, follow this segment. 

1. Reset The Error Code With A Scanner

Get yourself an OBD-II scanner to scan for the DTC P0678. Erase/reset the DTC with your scanner & check if it returns. Chances are, the code won’t return. 

Due to one or several intermittent issues, the DTC P0678 can appear. Other than that, falsely stored code is also possible. However, if you’re still getting the error code, follow the next methods. 

2. Check & Replace The #8 Cylinder Glow Plug

This error code heavily indicates a malfunction with the #8 cylinder glow plug; you should check the glow plug first. To make the inspection process easier, use a digital volt/ohm meter. 

First, remove the #8 cylinder glow plug from the cylinder top & start to investigate it. Use the digital volt/ohmmeter to measure the volts of the glow plug. 

If it’s between 0.5 to 2.0 ohm, it’s a good glow plug. Otherwise, your glow plug is probably faulty & needs to be replaced as soon as possible. 

3. Check & Replace The Glow Plug Relay or Timer

Firstly, you’ll have to spot the glow plug relay or timer. You should have found the glow plug timer in the engine compartment. To make it even more specific, check your main fuse box & you’ll find the glow plug relay/timer. 

The glow plug relay or timer controls all eight glow plugs. This relay works as a switch that turns off/on the glow plugs. Inspect the relay well & search for unwanted burnt signs. If you see anything unusual, replace it. 

4. Check & Replace Wires, Connectors & Fuses 

Finally, it’s time to check things that mostly remain ignored from our eyesight. Open the hood & inspect the wirings of the glow plug & glow plug relay. If you find damaged or burnt wires, replace them.

Like the wirings, you’ll have to check connectors & fuses. Blown fuses mandatorily require replacements. Also, you’ll have to replace the connectors if they are not looking okay from the visual inspection. 

How Much Does It Cost To Solve The Error Code P0678?

The total cost of solving the error code P0678 varies from vehicle to vehicle. You may need to replace one or several parts & all of them add up while doing the total sum of replacement.

That’s why you should know the replacement costs only. Later on, you can calculate your actual expected cost. Here are the replacement costs:

  • A Single Glow Plug Costs $10 to $12
  • Glow Plug Relay/Timer Costs $60 to $70
  • Wiring Connectors, Wires & Fuses Can Cost From $100 to $500

On top of the replacement cost, add another $75 to $150 per hour labor fee if you’re solving this code from an auto shop. 

Common Mistakes While Solving The P0678 Code

Humans are prone to make mistakes. Fixing the P0678 isn’t an exception & you might commit some mistakes while doing the job. Try avoiding these common mistakes mentioned below:

  1. Jumping Towards Replacing Relay/Timer at First, Start From The Glow Plug Instead.
  2. Wrongly Inspected Electrical Components Like Wires, Connectors & Fuses. 

Additional Comments To Consider Regarding The P0678 Code 

The P0678 itself isn’t a very dangerous trouble code. You’ll mostly suffer in the cold times when the vehicle may partially refuse to start. 

If you’re from a warm area, you might not notice any difference even if your one glow plug is faulty. Still, wherever you are – it’s a good idea to get rid of DTCs. 


I hope this article was helpful enough to know the P0678 error code thoroughly. Now you’ve almost every piece of information to diagnose the code properly. 

It’s up to you whether you’re doing all the work on your own, saving hundreds of bucks on labor fees. On the contrary, you can even hire a technician to do your job if needed.

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