P0678 OBD-II Trouble Code: Cylinder 8 Glow Plug Circuit

Our certified mechanics come to you · Get a fair and transparent estimate upfront

Red-stars EXCELLENT RATING ON

Cost of diagnosing the P0678 code

P0678 is a diagnostic trouble code (DTC) for "Cylinder 8 Glow Plug Circuit". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
Ford$20.00
Toyota$20.00
BMW$20.00
SCHEDULE P0678 DIAGNOSTIC Get a fair and transparent estimate upfront

P0678 code definition

The P0678 code detects an error with the glow plug circuit in cylinder 8

What the P0678 code means

The P0678 code is a generic OBD-II trouble code indicating a problem with the glow plug circuit in cylinder number 8. Glow plugs are used in diesel engines to help warm the engine to aid ignition. The powertrain control module (PCM) helps control this heat. When the voltage from the glow plug circuit in cylinder 8 is more than 10 percent off of the manufacturer’s suggested settings, then the PCM will be alerted, and the P0678 code will be detected.

What causes the P0678 code?

Many things can cause the P0678 trouble code to be stored, including:

  • Defective glow plugs
  • Defective glow plug relays
  • Malfunctioning glow plug timer or glow plug module
  • Blown fuses in the glow plug circuit
  • Issues with the electrical components in the glow plug circuit, such as open or short wires, or corroded, loose, or damaged connectors

What are the symptoms of the P0678 code?

The P0678 trouble code will usually be accompanied by the Check Engine Light, as well as the glow plug indicator warning light. The vehicle may take a while to start, especially in colder conditions. The vehicle may also experience white smoke emitting from the exhaust system during start-up.

How does a mechanic diagnose the P0678 code?

The P0678 code will be diagnosed using a standard OBD-II trouble code scanner. A reputable mechanic will use the scanner to assess the freeze frame data of the P0678 code, and look for any additional trouble codes that may be present. The mechanic will then reset the codes and restart the vehicle, to see if the code returns. If the code does not return, it is most likely an intermittent issue, or an incorrectly stored code.

If the P0678 code returns, then the technician will perform a visual inspection on the electrical components of the glow plug circuit. All wires, connectors, and fuses should be examined, and any that are damaged should be replaced.

Next, the mechanic can check to see if the glow plug is defective. This can be done using a digital volt/ohmmeter, or by hooking up a fully charged battery voltage to the glow plug on one end, and to the ground on the other end. If the glow plug is unable to heat up, or heats up to a bright red, then it is faulty and needs to be replaced.

If the issue is still unresolved, the relays, timers, and modules should be given thorough inspection.

Whenever a component is replaced, the trouble codes should be reset and the vehicle restarted. This way, the mechanic will be able to tell as soon as the issue has been fixed.

Common mistakes when diagnosing the P0678 code

The most common mistake made when diagnosing the P0678 codes comes from a failure to properly follow the OBD-II trouble code diagnosis protocol. The protocol should be followed exactly, to ensure that inspection and repairs are efficient.

It is common for timers and relays to be erroneously replaced, when the issue was the glow plug itself, or the electrical components.

How serious is the P0678 code?

If the P0678 code has been detected in the vehicle, it will still be drivable. However, there will be some issues, such as a prolonged start time, and issue should not be ignored.

What repairs can fix the P0678 code?

Repairs for the P0678 trouble code include:

Additional comments for consideration regarding the P0678 code

It is common for the P0678 code to be accompanied by other glow plug circuit trouble codes. When this is the case, codes should be inspected and repaired in the order that they appear in.

Since glow plugs are only used in diesel engines, the P0678 code will only apply to diesel vehicles.

Need help with a P0678 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

trouble codes
P0678
Check Engine Light

No more waiting rooms! Our mechanics will come to you to diagnose and fix the P0678 code.

SCHEDULE P0678 DIAGNOSTIC
Get a $20 credit for the follow-up repair

Recent Check Engine Light is on Inspection reviews

Excellent Rating


YourMechanic Check Engine Light is on Inspection Service

Average Rating

4.8/5

Number of Reviews

5,395

Rating Summary
4,978
202
50
30
135
4,978
202
50
30
135

Anthony

6 years of experience
18 reviews
Anthony
6 years of experience
Jeep Grand Cherokee - Check Engine Light is on - Carmichael, California
Anthony was great! We are very happy that we chose to go with this company instead of the overpriced and slow service we get from the Jeep dealership. He was on time and did the job just as expected. He identified a couple of other things that need to be done before the problems get worse. We appreciate having a technician give us direct feedback regarding our vehicle, rather than a service advisor (salesperson) that we've had to deal with in the past at the dealership. We'll be booking the addtional services very soon and will definitely request Anthony again now that he is familiar with our vehicle!

Michael

37 years of experience
113 reviews
Michael
37 years of experience
Subaru Forester - Check Engine Light is on - Santa Fe Springs, California
Michael was punctual and courteous. He knows what he’s doing and I would absolutely recommend him to anyone.

Anthony

6 years of experience
18 reviews
Anthony
6 years of experience
BMW 740Li - Check Engine Light is on - Roseville, California
Very helpful in finding out the fault codes in my bmw 740 li. It was simple fix and that the two tube hose just had to be connected and my drive train malfunction went away. This saved me from having to go the an expensive dealership. Anthony has a good attitude about his work.

Breck

19 years of experience
613 reviews
Breck
19 years of experience
Ram 1500 - Check Engine Light is on - Houston, Texas
Breck did a great job working on my truck. Showed up on time, found any issues I had on my truck and explained everything to me so that I understood what was going on. Went above and beyond, definitely will book him for future appointments.


More related articles

P0421 OBD-II Trouble Code: Warm Up Catalyst Efficiency Below Threshold (Bank 1)
P0421 Code Definition Warm Up Catalyst Efficiency Below Threshold (Bank 1) What the P0421 code means The P0421 code means that...
B1923 OBD-II Trouble Code: Air Bag Memory Clear Circuit Short To Ground
B1923 means there is an issue with the airbag system, likely due to a faulty memory module, bad battery, or defective electrical wiring.

Related questions

Check engine light on a lot

Hello Jacqueline! Thank you for writing in with this question. This problem could be related to a bad gas cap o-ring, or something more involved like an evaporative emissions system leak, or canister purge solenoid problem. Since the Check Engine...

P0171 and P0174 codes

For one, these codes are for a lean condition and are not O2 sensor specific codes. It is true that some of the newer Fords have an issue with the purge valve staying on, putting a vacuum on the system...

P0420 code and dash lighs on

The vehicle stability control (VSC) light and code P0420 are for two different problems. The VSC system would need to be tested for codes for that system. The code P0420 is for the O2 sensor or problem with...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com