P0078
Fix within a few daysExhaust Variable Valve Timing (VVT) Solenoid Circuit Malfunction (Bank 1)
Code P0078 means your exhaust VVT solenoid circuit on Bank 1 has a problem. Common causes: Faulty VVT solenoid (70%), wiring issues (15%), low/dirty oil (10%). Drivability: Yes, for short trips. Repair cost: $50-$200 DIY, $150-$500 professional.
Can I Drive With P0078?
Yes, for short trips only
Essential trips under 10 miles, avoid highways and heavy acceleration. Monitor engine behavior closely.
Stop driving immediately if: Flashing Check Engine Light, loud engine noises, significant power loss, or engine stalling
Symptoms of P0078
- 1Check Engine Light is on
- 2Rough or erratic idle
- 3Reduced engine power or acceleration
- 4Decreased fuel economy
- 5Engine stalling
- 6Engine noise (ticking or rattling)
Common Causes of P0078
Parts most likely causing this code, ranked by probability
The solenoid itself has an internal electrical fault or is mechanically stuck, preventing proper oil flow to the VVT actuator.
70% of P0078 cases are fixed by replacing this part
Damaged, corroded, or loose wiring or a faulty connector prevents the correct electrical signal from reaching the solenoid.
15% of P0078 cases are fixed by repairing wiring or connector
Low engine oil or excessively dirty/sludgy oil prevents the VVT system from operating correctly, as it relies on oil pressure.
10% of P0078 cases are fixed by addressing oil issues
An internal fault within the engine computer can prevent it from sending the correct command signal to the VVT solenoid.
5% of P0078 cases are fixed by replacing or reprogramming the ECM
Check These First (Before Buying Parts)
- Check your engine oil level and ensure it's full and clean. Low or dirty oil is a common cause of VVT issues.
- Visually inspect the electrical connector and wiring going to the exhaust VVT solenoid on Bank 1 for any obvious damage, corrosion, or loose connections.
How to Diagnose P0078
- 1Check engine oil level and condition; ensure it's full and clean.
- 2Visually inspect the exhaust VVT solenoid (Bank 1) wiring and connector for any signs of damage, corrosion, or looseness.
- 3Disconnect the VVT solenoid and check its electrical resistance with a multimeter; compare to factory specifications.
- 4If possible, swap the exhaust VVT solenoid with the intake VVT solenoid (if accessible and identical) to see if the code moves.
- 5Inspect the VVT solenoid's oil screen for clogs or debris after removal.
- 6Use a scan tool to monitor VVT solenoid command and actual position, and check for proper voltage supply.
P0078 on Popular Vehicles
Honda Accord
2003-2024Honda engines are sensitive to oil quality and level for VVT operation. P0078 often points to a failing exhaust VVT solenoid or a clogged oil screen within the solenoid.
75% fixed by replacing VVT solenoid or oil change
Toyota Camry
2007-2024Toyota's VVT-i systems can trigger P0078 due to a faulty exhaust VVT solenoid. Inspecting the wiring harness for rodent damage is also a good idea, as it's a common issue.
70% fixed by replacing VVT solenoid
Ford F-150
2004-2024On Ford F-150s with VVT (Ti-VCT), P0078 can indicate a problem with the exhaust VVT solenoid on Bank 1. These engines are also sensitive to proper oil viscosity and pressure.
65% fixed by replacing VVT solenoid
Frequently Asked Questions
What does P0078 mean?
P0078 indicates an electrical circuit malfunction with the exhaust variable valve timing (VVT) solenoid on Bank 1 of your engine. This solenoid controls the timing of your exhaust valves.
Can I drive with P0078?
Yes, you can drive for short trips, but limit driving. If you notice significant power loss, rough idling, or stalling, stop driving immediately. Fix this within a few days to prevent further issues.
Will P0078 clear itself?
No, P0078 will not clear itself. The underlying electrical or mechanical issue needs to be diagnosed and repaired. Once fixed, you can clear the code with a scan tool.
How do I fix P0078 myself?
Start by checking your engine oil level and condition. Then, inspect the VVT solenoid's wiring and connector. If those are good, replacing the exhaust VVT solenoid on Bank 1 is the most common fix.
How much does it cost to fix P0078?
A DIY fix for P0078 typically costs $50-$200 for a new VVT solenoid. Professional repair at a shop ranges from $150-$500, including diagnosis and labor.
P0078 keeps coming back - why?
If P0078 keeps returning, it often means the initial diagnosis was incomplete. Common reasons include a persistent wiring issue, a clogged oil passage affecting the new solenoid, or a rare ECM fault.
Will P0078 fail emissions/smog test?
Yes, P0078 will cause your vehicle to fail an emissions or smog test. The Check Engine Light being on automatically results in a failed inspection in most states.
What's the difference between P0078 and P0079?
P0078 indicates a circuit malfunction (electrical issue) with the exhaust VVT solenoid on Bank 1. P0079 indicates a performance issue (stuck open/closed or slow response) with the same solenoid, which can be mechanical.
P0078 on Honda Accord - what's common?
On Honda Accords, P0078 is often caused by a faulty exhaust VVT solenoid, sometimes due to internal electrical failure or sludge buildup. Checking oil level and condition is always the first step.
Questions to Ask Your Mechanic
Did you check the engine oil level and condition before diagnosing the VVT solenoid?
Good answer: Yes, the first step was to confirm the oil was at the correct level and not excessively dirty or sludgy, as VVT systems rely on clean oil.
What were the resistance readings for the exhaust VVT solenoid, and how do they compare to specifications?
Good answer: I measured the resistance at X ohms, and the factory specification is Y ohms. The reading was out of range, indicating an internal fault in the solenoid.
Did you inspect the wiring and connector to the VVT solenoid for any damage or corrosion?
Good answer: Yes, I thoroughly checked the wiring harness and connector for any signs of fraying, breaks, or corrosion. Everything looked good there, so the issue is internal to the solenoid.
Repair Cost Estimate
DIY Repair
Parts only
$50-$200
Shop Repair
Parts + labor
$150-$500
Save $100-$300 by doing it yourself
Difficulty
intermediate
Time
1-2 hours
Intermediate - requires basic mechanical skills, a multimeter for testing, and careful attention to detail. Access to the solenoid can vary by vehicle.
Cost of Waiting
Ignoring P0078 can lead to permanently reduced engine power, poor fuel economy, and increased emissions. In severe cases, if the VVT system is stuck in an extreme position, it can cause engine damage over time due to improper valve timing. A $100 solenoid replacement now prevents potential engine repairs later.
While You're In There...
VVT systems are highly dependent on clean engine oil. If your oil is dirty or due for a change, replacing it ensures proper VVT operation and prevents future issues.
If the intake VVT solenoid is easily accessible and your vehicle has high mileage, replacing both solenoids on Bank 1 at the same time can prevent a repeat repair, as they often wear out similarly.
Tools You'll Need
- Basic hand tools (sockets, wrenches)
- Multimeter
- Engine oil (if needed)
- Scan tool (optional, for clearing code and live data)
P0078 is a common VVT system code. Most repairs involve replacing a relatively inexpensive solenoid, and your engine will regain its full performance and efficiency afterward.
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Your Next Steps
Step 1: Check your engine oil level and condition. Top off or change the oil and filter if needed. Clear the code and see if it returns.
Step 2: If the code returns, visually inspect the exhaust VVT solenoid's wiring and connector for damage. If no damage is found, use a multimeter to test the solenoid's resistance. Replace the solenoid if it's out of specification.
Step 3: If the solenoid tests good and the code persists, consider inspecting the VVT oil passages for clogs or consulting a professional for advanced diagnostics, including oil pressure checks and ECM testing.