P3400
Moderate Severity (Level 3)Faulty Cylinder Deactivation System
P3400 usually means faulty Cylinder Deactivation System.
Can you still drive with P3400?
⚠️Short-distance driving is usually OK, but have this diagnosed within a week to prevent further damage.
Typical repair cost: $80 – $1200
Severity Level 3 — Moderate
This code indicates a moderate issue that may affect vehicle performance and fuel economy. Continued driving is possible in most cases, but prompt diagnosis and repair are recommended to prevent further damage.
Common Symptoms
- Check Engine Light illuminated
- Warning light or malfunction indicator related to the powertrain/engine system is illuminated
- The powertrain/engine system is not operating as designed
- Diagnostic trouble code (DTC) stored in module memory
Possible Causes
- Faulty engine sensor or actuator — most common cause, test before replacing
- Damaged or corroded wiring/connector in the powertrain/engine system circuit
- Blown fuse or faulty relay for the powertrain/engine system
- Poor ground connection — check and clean all related ground points
- Control module fault — rare but possible, only consider after ruling out simpler causes
Common Fixes
- Scan vehicle with a professional-grade OBD2 scanner to read all stored codes and freeze frame data — note the conditions when the code set ($46-147 at shop, free at auto parts store for basic scan)
- Visually inspect the powertrain/engine system wiring harness and connectors — look for chafed wires, melted insulation, green corrosion, loose pins, or rodent damage (often free to check yourself, $77 diagnostic fee at shop)
- Replace engine sensor or actuator if testing confirms it has failed — use OEM quality, avoid the cheapest no-name aftermarket parts that fail in a year ($80-1200)
- Check and replace any blown fuses in the powertrain/engine system fuse circuit — if fuse blows again, there's still a short that needs to be found ($4-13 for fuses)
- Perform a wiggle test on the powertrain/engine system wiring harness while monitoring live data — see if the fault returns when you move the harness at different points ($0-133 diagnostic labor)
Estimated Repair Cost
These are estimated costs based on generic repair data. Actual costs may vary depending on your vehicle, location, and labor rates.
Frequently Asked Questions
What does P3400 mean?
P3400 stands for "Faulty Cylinder Deactivation System". P3400 usually means faulty Cylinder Deactivation System.
Can you drive with P3400?
Short-distance driving is usually OK, but have this diagnosed within a week to prevent further damage.
How much does it cost to fix P3400?
Repair costs for P3400 typically range from $80 to $1200, depending on your vehicle make, model, and local labor rates. Common fixes include: Scan vehicle with a professional-grade OBD2 scanner to read all stored codes and freeze frame data — note the conditions when the code set ($46-147 at shop, free at auto parts store for basic scan); Visually inspect the powertrain/engine system wiring harness and connectors — look for chafed wires, melted insulation, green corrosion, loose pins, or rodent damage (often free to check yourself, $77 diagnostic fee at shop); Replace engine sensor or actuator if testing confirms it has failed — use OEM quality, avoid the cheapest no-name aftermarket parts that fail in a year ($80-1200).
Will P3400 clear itself?
Explore Repair Costs
Related OBD-II Codes
These codes are in the same range as P3400 and often share similar causes and fixes.
Worried about repair costs?
Get transparent estimates and verify your mechanic's quote before authorizing repairs.
Related Discussions
See what other car owners are saying about this code and related repairs.
View P3400 discussions in the community