P3421 code meaning
Cylinder 3 Exhaust Valve Control Circuit/Open
Powertrain system Generic code P34xx codes Check engine light
What P3421 means
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.
P3421 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 P3421
- Check engine lamp on
- Cylinder deactivation locked out
Common causes of P3421
- PossibleBroken lead or loose terminal at the cylinder 3 exhaust actuator
- PossibleExhaust actuator winding interrupted
- Less likelyFault in the control module output
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 P3421 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). |
| 21 | The exact fault in that area. |
What to do next
- Note P3421 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 P3421
What does P3421 mean?
P3421 means "Cylinder 3 Exhaust Valve Control Circuit/Open". P3421 opens the exhaust group of cylinder 3 and stands for an interrupted circuit to an actuator that would switch only the exhaust valves. It is a generic code, so it means the same on every make.
Is it safe to drive with P3421?
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 P3421 fail an emissions test?
Yes, it can. P3421 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 P3421 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 P3421 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.