Powertrain, shared range

P3420 Cylinder 3 Deactivation/Intake Valve Control Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P3420 reports that the cylinder 3 deactivation control line carries supply voltage where the module expects to pull it low. On GM's L84 the test runs only while the low-side output is switched on: a connection to battery voltage below 0.5 ohm, confirmed in 20 out of 25 samples, sets a Type B code. According to NHTSA's 2025 investigation into GM's DFM V8s, every cylinder has exactly one lifter oil solenoid, run by a peak-and-hold driver, so a single short disables the whole cylinder's switching. The Gen IV controller also has a separate high-side stage for this solenoid with its own codes, which helps tell which half of the circuit failed. P3419 covers the short to ground. The engine just keeps all eight cylinders working.

Likely causes

Control wire of cylinder 3 touching a powered conductor
Shorted turns in the cylinder 3 solenoid winding
Output transistor in the engine control module damaged

Symptoms

  • Check engine lamp on
  • Fuel economy mode unavailable

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

P3417P3418P3419P3424P3428P3412

References: law.cornell.edu, gsi.ext.gm.com, static.nhtsa.gov.