P3405: Cylinder 1 Deactivation Circuit High Voltage
The engine control module has detected high voltage or a short to power in the cylinder 1 deactivation control circuit.
What P3405 means
P3405 is a generic OBD-II powertrain code in the hybrid & EV group. In plain English: the computer sees a voltage on that circuit that is higher than it should ever be — often an open ground, a short to power, or a failed sensor.
- Check engine light
- Usually on
- Emissions-related
- Yes — can fail inspection
- Limp mode possible
- Not typical
- Drive cycle to clear
- Required
Get it fixed
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Common causes
- 01Wiring shorted to powerMost likely
- 02Solenoid open circuitPossible
- 03Connector pins corroded - high contact resistanceLess likely
Can I drive with P3405?
Have it checked before relying on the car.
High-voltage faults can shut the drive system down without much warning. Do not open orange high-voltage components; this needs a trained technician.
Why we rate it urgent
- High-voltage system fault: the car may shut down or refuse to start
- Turns on the check engine light
- Emissions-related: will usually fail an OBD inspection
- Needs a drive cycle to confirm a repair
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose P3405
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just P3405. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Check for related codes first
Look for P3409. Related codes often share a cause; a circuit or sensor code usually needs fixing before a performance code like this one.
- 3
Test the circuit
Inspect the wiring and connector at the cylinder deactivation solenoid and engine wiring harness for damage, corrosion or chafing. With a multimeter, check supply voltage, ground and signal against the specifications in the service manual for your vehicle.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Wiring shorted to power; solenoid open circuit; connector pins corroded - high contact resistance. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and complete a full drive cycle (cold start, idle, steady highway cruise, deceleration). The code is fixed when the related readiness monitor completes without it returning.
P3405 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Moderate
- Good DIY job?
- Usually a shop job
Needs a scan tool and some experience with testing.
Parts and systems involved
- Cylinder deactivation solenoid
- Engine wiring harness
P3405 FAQ
What does P3405 mean?
P3405 means “Cylinder 1 Deactivation Circuit High Voltage”. The engine control module has detected high voltage or a short to power in the cylinder 1 deactivation control circuit.
Is P3405 serious? Can I keep driving?
We rate P3405 as urgent severity. Have it checked before relying on the car. High-voltage faults can shut the drive system down without much warning. Do not open orange high-voltage components; this needs a trained technician.
What causes P3405?
The most common causes, from most to least likely: Wiring shorted to power; Solenoid open circuit; Connector pins corroded - high contact resistance. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix P3405?
Typical labor is about $125–$500 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix P3405 myself?
DIY difficulty is moderate. Most owners leave this to a shop because it needs involved testing or specialist tools. Always confirm the cause before buying parts.
Will P3405 clear itself?
Once the fault is fixed, the check engine light usually goes off by itself after the system passes its self-test over several drive cycles. Clearing the code with a scan tool resets readiness monitors, so an inspection station may turn you away until a full drive cycle is completed.