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P3420 Cylinder 3 Deactivation/Intake Valve Control Circuit High GuideMechanic.Com Modern engines are designed to maximize fuel efficiency, reduce emissions, and optimize performance across varying loads and driving conditions.
One of the technologies enabling this balance is cylinder deactivation, commonly used in V6 and V8 engines. Diagnostic Trouble Code (DTC) P3420 refers specifically to a problem in cylinder 3’s deactivation system or its associated intake valve control circuit.
This article provides a comprehensive understanding of what this code means, its possible causes, symptoms, diagnostic procedures, and repair options.
See Also: P341A P341B P341C P341D P341E P341F ISO/SAE Reserved
P3420 Cylinder 3 Deactivation/Intake Valve Control Circuit High
What Does DTC P3420 Mean?
Code Definition:
P3420 – Cylinder 3 Deactivation/Intake Valve Control Circuit High
This code is stored when the Powertrain Control Module (PCM) detects an abnormally high voltage condition in the intake valve control circuit for cylinder 3, specifically related to cylinder deactivation mechanisms.
Many modern engines, particularly in General Motors (GM), Chrysler, Honda, and others, deactivate certain cylinders under light load to improve fuel economy. This is often referred to as Active Fuel Management (AFM), Displacement on Demand (DoD), or Variable Cylinder Management (VCM) depending on the manufacturer.
The intake valve control solenoids for each cylinder play a critical role in enabling or disabling airflow to the combustion chamber. If the control circuit for cylinder 3 reports a voltage level higher than expected, the PCM flags this as DTC P3420.
Where Does Cylinder 3 Fit In?
In V6 or V8 engine configurations:
Cylinder 3 is typically located on the passenger side (right bank) in the firing order.
The exact placement can vary by manufacturer, so consulting the service manual is essential for accurate identification.
P3420 Cylinder 3 Deactivation/Intake Valve Control Circuit High
Symptoms of a P3420 Code
When DTC P3420 is present, the vehicle may exhibit one or more of the following symptoms:
- Check Engine Light (CEL) is illuminated.
- Rough engine idle, especially during low-load conditions.
- Reduced engine performance, particularly under light throttle.
- Increased fuel consumption due to loss of deactivation function.
- Engine misfire codes may accompany this DTC (such as P0303 for Cylinder 3).
- Noise or ticking from the engine in certain conditions.
- In many cases, the vehicle may still drive, but with degraded efficiency or performance.
Possible Causes of P3420
Several components and factors may trigger this code. Common causes include:
Faulty Cylinder Deactivation Solenoid (Intake Valve Solenoid)
A malfunctioning solenoid may be stuck open or closed, or may be electrically shorted/high resistance.
Wiring Issues
Open, short to power, or high resistance in the solenoid control circuit wiring or connectors.
Poor Electrical Ground
A poor ground circuit can cause abnormal voltage readings in the solenoid circuit.
PCM/ECM Failure
Though rare, a fault in the control module could misinterpret circuit voltages.
Dirty or Sludged Oil
Hydraulic systems like cylinder deactivation depend on clean, pressurized oil. Dirty oil may cause solenoids to stick or not function properly.
Mechanical Failure
Issues with the lifter, rocker arm, or valve mechanism related to cylinder 3 could affect operation and trigger the code.
P3420 Cylinder 3 Deactivation/Intake Valve Control Circuit High
How to Diagnose P3420
Proper diagnosis is key to avoid unnecessary parts replacement. Here’s a step-by-step process a technician might follow:
1. Verify the Code
Use a professional scan tool to confirm DTC P3420 is active.
Check for other related codes such as P0303 (Cylinder 3 misfire) or other cylinder deactivation codes.
2. Visual Inspection
Inspect the intake valve control solenoid connector on cylinder 3 for damage, corrosion, or loose pins.
Check wiring harnesses for chafing, melting, or disconnection.
3. Test the Solenoid
Use a digital multimeter to check the resistance of the intake valve solenoid. A value outside the manufacturer’s spec suggests a bad solenoid.
Apply 12V (bench test) to verify if the solenoid actuates.
4. Check Voltage Levels
Use a scan tool or oscilloscope to monitor real-time voltage on the solenoid control circuit.
A “high” voltage reading may indicate a short to power or an open in the ground path.
5. Oil Inspection
Check the oil level and condition. Replace dirty or low oil as it can impede proper solenoid operation.
6. PCM Testing
If all other components test good, suspect the PCM. It should be tested by a dealer or with advanced diagnostic equipment.
P3420 Cylinder 3 Deactivation/Intake Valve Control Circuit High
How to Fix P3420
The appropriate fix will depend on the diagnosed cause. Here are the most common repair actions:
Replace the Cylinder 3 Intake Valve Control Solenoid
This is often the culprit, especially if resistance or activation tests fail.
Repair or Replace Damaged Wiring or Connectors
Corroded pins, broken wires, or insulation damage can be repaired or replaced.
Change the Engine Oil and Filter
Use manufacturer-recommended oil grades. Dirty or sludged oil can disrupt solenoid and lifter operation.
Repair or Replace Engine Valve Train Components
If there’s a mechanical issue like a failed lifter or rocker arm, internal engine repair may be needed.
Update or Replace PCM/ECM
If all else fails and PCM failure is confirmed, a new or reprogrammed control module may be required.
P3420 Cylinder 3 Deactivation/Intake Valve Control Circuit High
Prevention Tips
Use High-Quality Engine Oil: Cylinder deactivation solenoids rely on clean hydraulic pressure. Regular oil changes using the correct oil grade are essential.
Avoid Short Trips: These don’t allow the engine to reach optimal operating temperature, contributing to sludge buildup.
Use OEM Parts: Aftermarket solenoids may not meet the same electrical tolerances and reliability standards.
Manufacturer TSBs and Known Issues
Some manufacturers, especially GM and Chrysler, have issued Technical Service Bulletins (TSBs) for similar codes. These TSBs may outline:
Updated solenoid designs
Revised PCM software calibrations
Known wiring harness issues in specific engine configurations
Before replacing components, check if your vehicle is affected by a TSB or recall.
Conclusion
DTC P3420 (“Cylinder 3 Deactivation/Intake Valve Control Circuit High”) indicates an issue with the electrical circuit or function of the intake valve control for cylinder 3, often tied to advanced fuel-saving technologies.
While the code may seem intimidating due to its technical nature, careful diagnostics and understanding of the underlying system can lead to effective repair.
Ignoring this code may not immediately harm the engine, but it will reduce fuel efficiency, trigger emissions issues, and potentially cause further engine damage if left unaddressed.
Whether you’re a technician or a DIY mechanic, knowing how to approach this fault code will save time, money, and frustration.
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