P3420 — Cylinder 3 Deactivation/Intake Valve Control Circuit High

P3420 — Cylinder 3 Deactivation/Intake Valve Control Circuit High. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: control module driver fault, faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector.

For Ford vehicles

cylinder 3 deactivation/intake valve control circuit – signal too high

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

  1. Read the code and freeze frame Connect an OBD2 scanner, confirm P3420 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the cylinder 3 deactivation/intake valve control for damage, corrosion, chafing or poor contact.
  4. Subsystem check With the cylinder 3 deactivation/intake valve control disconnected, measure signal voltage at the harness connector: a high reading with the component unplugged indicates a short to power in the harness; if it drops to normal, the component itself is faulty.
  5. Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
  6. Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
  7. Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P3420 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P3420 (parts and labor, USD, independent shop rates): Repair wiring or connectors: $80–$250; Control module repair: $300–$1,000; Replace the faulty sensor or actuator: $150–$500. Overall, fixing P3420 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

How much does it cost to fix P3420?

Repair wiring or connectors — $80–$250; Control module repair — $300–$1,000; Replace the faulty sensor or actuator — $150–$500. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What is the most common cause of P3420?

The most common causes are: control module driver fault, faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector.

Will P3420 clear itself?

Sometimes P3420 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What does OBD2 code P3420 mean?

P3420 — Cylinder 3 Deactivation/Intake Valve Control Circuit High. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: control module driver fault, faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector.

Is it safe to drive with P3420?

In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

What does P3420 mean?

P3420 (Cylinder 3 Deactivation/Intake Valve Control Circuit High) is stored when self-diagnostics detect abnormal readings or behaviour of the sensor and actuator circuits. It belongs to the powertrain (engine/transmission) category.

P3420 refers specifically to cylinder 3. On inline engines cylinders are counted from the front (belt end); on V-engines the numbering depends on the manufacturer, so check the firing-order diagram for your exact model. Location matters for the repair bill: some cylinders require intake manifold removal, which adds labor time.

“Circuit high” means the control module sees a voltage on the cylinder 3 deactivation/intake valve control circuit that is above the expected range — typically close to battery voltage. Physically this points to a short to a power feed, a broken ground return, or a failed component pulling the signal line high.

To set P3420, the control module compares live readings of the sensor and actuator circuits against calibrated limits, usually over several drive cycles. Alongside the code it stores a freeze frame — a snapshot of rpm, load, coolant temperature and vehicle speed at the moment of failure. Reading that snapshot first saves diagnostic time.

Common symptoms of P3420

  • the affected system operates intermittently or not at all
  • Check Engine Light on
  • possible limp mode depending on the affected component
  • increased fuel consumption in some cases

What causes P3420?

  • open ground return of the cylinder 3 deactivation/intake valve control
  • signal wire shorted to battery positive
  • failed cylinder 3 deactivation/intake valve control pulling the signal high
  • poor ground connection
  • blown fuse feeding the circuit
  • open or shorted wiring in the circuit
  • control module driver fault
  • corroded, loose or damaged connector

How to diagnose P3420

  1. Connect an OBD2 scanner, confirm P3420 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Visually inspect the wiring harness and connectors related to the cylinder 3 deactivation/intake valve control for damage, corrosion, chafing or poor contact.
  4. With the cylinder 3 deactivation/intake valve control disconnected, measure signal voltage at the harness connector: a high reading with the component unplugged indicates a short to power in the harness; if it drops to normal, the component itself is faulty.
  5. Measure reference voltage, ground and signal continuity at the component connector.
  6. Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
  7. Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P3420 does not return.

How to fix P3420

Start with the cheapest and most common causes before replacing expensive parts:

  • Repair wiring or connectors — $80–$250
  • Control module repair — $300–$1,000
  • Replace the faulty sensor or actuator — $150–$500

How much does it cost to fix P3420?

Repair cost depends on which component actually failed. Typical scenarios for P3420 (parts and labor, USD, independent shop rates):

  • Repair wiring or connectors: $80–$250
  • Control module repair: $300–$1,000
  • Replace the faulty sensor or actuator: $150–$500

Overall, fixing P3420 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with P3420?

In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

Related OBD2 codes