Powertrain, shared range

P3421 Cylinder 3 Exhaust Valve Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P3421 opens the exhaust group of cylinder 3 and stands for an interrupted circuit to an actuator that would switch only the exhaust valves. No manufacturer documents this code publicly. Engines that are known to idle cylinder 3, such as GM's LTA and LT2 V8s (bulletin 20-NA-038) and the L84, let one lifter control both valves of the cylinder, so an open circuit there shows up as P3417. A GM patent application on deactivation hardware keeps a single oil-switching valve and only shapes the cam timing so that the exhaust side drops out first and returns first. Should a design ever give the exhaust side its own actuator, CARB's continuity check for outputs would apply to it. The owner would see a warning lamp and lose the economy mode.

Likely causes

Broken lead or loose terminal at the cylinder 3 exhaust actuator
Exhaust actuator winding interrupted
Fault in the control module output

Symptoms

  • Check engine lamp on
  • Cylinder deactivation locked out

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

P3422P3423P3424P3417P3413P3429

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