P340C code meaning
Deactivation/Exhaust Valve Control Circuit Bank 1
Powertrain system Generic code P34xx codes Check engine light
What P340C means
P340C concerns a separate electrical circuit that disables the exhaust valves of bank 1 as a group. A fault in its wiring, connector or actuator coil sets the code. No manufacturer documents it publicly, and none of the known production systems needs it: GM's DFM engines feed the intake and exhaust lifters of each cylinder from one shared solenoid, and a GM patent application describes one hydraulic valve per pair of cylinders that drops the exhaust valves before the intake valves purely by cam timing. Under CARB rules every output of this type needs an electrical integrity test. The intake-side circuit is P340A, bank 2 exhaust P340D, the bank 1 exhaust function P341C. Drivers mainly see the lamp; deactivation is suspended.
P340C at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P340C
- Check engine lamp on
- Reduced-cylinder mode not available
Common causes of P340C
- PossibleOpen or shorted wire in the bank 1 exhaust actuator circuit
- PossibleExhaust deactivation actuator coil open or shorted
- Less likelyConnector or wiring damaged by heat near the exhaust side
- Less likelyEngine control module output stage fault
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Cylinder deactivation solenoidWiring harnessECM
What each part of P340C means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 3 | Mixed range: generic and manufacturer-specific codes. |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 0C | The exact fault in that area. |
What to do next
- Note P340C and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P340C
What does P340C mean?
P340C means "Deactivation/Exhaust Valve Control Circuit Bank 1". P340C concerns a separate electrical circuit that disables the exhaust valves of bank 1 as a group. It is a generic code, so it means the same on every make.
Is it safe to drive with P340C?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P340C fail an emissions test?
Yes, it can. P340C is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P340C to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P340C clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.