Powertrain, shared range

P340C Deactivation/Exhaust Valve Control Circuit Bank 1

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

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.

Likely causes

Open or shorted wire in the bank 1 exhaust actuator circuit
Exhaust deactivation actuator coil open or shorted
Connector or wiring damaged by heat near the exhaust side
Engine control module output stage fault

Symptoms

  • Check engine lamp on
  • Reduced-cylinder mode not available

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–900
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

cylinder deactivation solenoidwiring harnessecm

Related codes

P340AP340DP341CP3400P3405

References: law.cornell.edu, patents.google.com, static.nhtsa.gov.