Quick Answer
P0678 means: P0678 indicates a high input voltage in the glow plug circuit for cylinder 8, affecting diesel engine performance.
Can I drive with P0678? Immediate attention is recommended to prevent further engine issues.
Common Questions
What does P0678 mean and how does it affect my car?
The P0678 code indicates an issue with the glow plug circuit in cylinder 8, which could cause hard starting, rough idling, and increased emissions. This can lead to poor performance and possible damage to the engine over time.
What are the most common causes of P0678 and how much does it cost to fix?
Common causes include faulty glow plugs, short circuits in wiring, and issues with the ECM. Repair costs can range from $150 for glow plug replacement to $800 for ECM replacement.
Can I drive my car with P0678 or should I stop immediately?
While it may be possible to drive with a P0678 code, it is not advisable due to potential engine damage. It's best to address the issue promptly to avoid further complications.
How can I diagnose P0678 myself using GeekOBD APP?
To diagnose P0678, connect the GeekOBD APP to your OBD2 port, scan for codes, and check freeze frame data to understand the conditions under which the code was triggered. This will guide your next steps.
What vehicles are most commonly affected by P0678?
The P0678 code is frequently seen in 2003-2005 Ford Super Duty trucks, including F-250 and F-350 models. Owners should be aware of this issue, especially in colder climates.
How can I prevent P0678 from happening again?
Regular maintenance, including checking the glow plugs and wiring, can prevent issues. Additionally, ensure that your vehicle's battery is in good condition, as a weak battery can affect glow plug performance.
What is P0678?
The P0678 diagnostic trouble code (DTC) indicates that there is a problem with the glow plug circuit for cylinder 8 in diesel engines. Glow plugs are crucial for starting a diesel engine, especially in cold weather, as they heat the air in the combustion chamber to ensure smooth ignition. When the Engine Control Module (ECM) detects an unusually high input voltage from the glow plug circuit of cylinder 8, it triggers this trouble code. This can lead to hard starting, rough idling, and increased emissions. If left unaddressed, it could cause further engine problems, including potential damage to the diesel particulate filter (DPF) due to incomplete combustion. Owners of vehicles such as the Ford F-250 and F-350 should be particularly aware, as these models frequently experience this issue, especially those manufactured between 2003 and 2005. Addressing this code promptly is not only essential for vehicle performance but also critical for maintaining compliance with emissions regulations.
System: P - Powertrain (Engine, Transmission, Emissions)
Symptoms
Common symptoms when P0678 is present:
- Check engine light illuminates, remaining on until the issue is resolved.
- Difficulties starting the engine, especially during cold weather, causing frustration for drivers.
- Engine may run rough or misfire during idle, leading to an uncomfortable driving experience.
- Decreased fuel economy, potentially dropping by 10-20% due to inefficient combustion.
- Possible white smoke from the exhaust, indicating incomplete combustion as a result of poor glow plug performance.
Possible Causes
Most common causes of P0678 (ordered by frequency):
- The most common cause of P0678 is a faulty glow plug, with a likelihood of 60%. Over time, glow plugs can wear out or fail due to heat and corrosion.
- A short circuit in the wiring harness can also trigger this code, occurring in about 20% of cases. This may be due to damaged insulation or loose connections.
- An issue with the engine control module (ECM) itself can cause erroneous readings, which is less common but still possible. Routine checks can help prevent this.
- Corrosion at the glow plug connectors can disrupt the electrical flow, contributing to the problem. Regular maintenance can help prevent this scenario.
- A blown fuse in the glow plug circuit, while rare, could also trigger a P0678 code. This should be checked if other components appear functional.
P0678 Repair Costs
Cost Breakdown by Repair Type
Glow Plug Replacement
Replacing the faulty glow plug in cylinder 8, including labor and parts.
- Total: $150 - $300
- Success rate: 85%
Wiring Repair
Fixing or replacing damaged wiring and connectors in the glow plug circuit.
- Total: $100 - $200
- Success rate: 90%
ECM Reprogramming
Reprogramming or replacing the ECM if it's determined to be faulty.
- Total: $300 - $800
- Success rate: 75%
Money-Saving Tips for P0678
- Start with the most common and least expensive repairs first
- Use GeekOBD APP to confirm diagnosis before replacing expensive parts
- Consider preventive maintenance to avoid future occurrences
- Compare prices for OEM vs aftermarket parts based on your needs
- Address the issue promptly to prevent more expensive secondary damage
Diagnostic Steps
Professional P0678 Diagnosis Process
Follow these systematic steps to accurately diagnose P0678. Each step builds on the previous one to ensure accurate diagnosis.
Step 1: Step 1: Conduct an initial visual inspection
Step 1: Conduct an initial visual inspection. Examine the glow plug wiring for any signs of damage, corrosion, or loose connections (5-10 minutes).
Step 2: Step 2: Use the GeekOBD APP to perform an OBD2 scan
Step 2: Use the GeekOBD APP to perform an OBD2 scan. Retrieve all stored trouble codes and freeze frame data to gain context about the P0678 code (10-15 minutes).
Step 3: Step 3: Test the glow plug with a multimeter to check its resistance and functionality
Step 3: Test the glow plug with a multimeter to check its resistance and functionality. This will help confirm if it needs replacement (20-30 minutes).
Step 4: Step 4: After replacing any defective components, perform a system function test to ensure everything operates correctly
Step 4: After replacing any defective components, perform a system function test to ensure everything operates correctly. Clear codes from the ECU (10-15 minutes).
Step 5: Step 5: Conduct a road test under various driving conditions to verify that the issue has been resolved and monitor for any reoccurrence of symptoms (15-20 minutes)
Step 5: Conduct a road test under various driving conditions to verify that the issue has been resolved and monitor for any reoccurrence of symptoms (15-20 minutes).
Important Notes
- Always verify the repair with GeekOBD APP after completing diagnostic steps
- Clear codes and test drive to ensure the problem is resolved
- Address underlying causes to prevent code recurrence
Real Repair Case Studies
Case Study 1: Glow Plug Replacement in 2004 Ford F-350
Vehicle: 2004 Ford F-350, 120,000 miles
Problem: Customer reported difficulty starting the vehicle in cold weather and a persistent check engine light.
Diagnosis: Diagnostic scan revealed P0678. Visual inspection showed a burnt-out glow plug.
Solution: Replaced the faulty glow plug in cylinder 8 and cleared the engine codes.
Cost: $180 (including parts and labor)
Result: The vehicle started reliably, and the check engine light remained off after the repair.
Case Study 2: Wiring Repair in 2003 Ford F-250
Vehicle: 2003 Ford F-250, 150,000 miles
Problem: Customer experienced rough idling and a lack of power during acceleration.
Diagnosis: P0678 was confirmed, and further inspection revealed frayed wiring in the glow plug circuit.
Solution: Repaired the damaged wiring and replaced connectors as needed.
Cost: $120 (for labor and materials)
Result: Performance improved significantly, and the customer reported smooth operation.