Fix P3401: Mechanic’s solutions that WORKED

The P3401: Cylinder 1 Deactivation/Intake Valve Control Circuit/Open code indicates a fault in the Cylinder 1 Deactivation/Intake Valve Control Circuit, suggesting an open circuit or malfunction. This is critical for vehicles equipped with a system designed to deactivate certain cylinders under specific conditions to improve fuel efficiency. The issue primarily lies in the malfunctioning components controlling cylinder deactivation for cylinder 1, which can significantly impact the engine’s performance.

P3401 quick overview

Meaning	P3401: Cylinder 1 Deactivation/Intake Valve Control Circuit/Open
Is it serious?	Yes, this code can be serious as it may lead to engine performance issues, including misfires, poor fuel economy, and in some cases, the vehicle may not run smoothly.
Possible causes	– Faulty MDS (Multi-Displacement System) solenoid – Wiring or connector issues related to the MDS solenoid – Faulty or sticking valve lifters – Powertrain Control Module (PCM) issues – Damaged coil pack or high secondary resistance in a coil
How to diagnose?	Check MDS Solenoid Operation: Confirm the operation of the MDS solenoid for cylinder 1. Inspect Wiring and Connectors: Examine all related wiring and connectors for damage or corrosion. Test Coil and Spark Plugs: Evaluate the condition and operation of the coil pack and spark plugs. Verify Proper Grounding: Ensure all circuits have proper grounding. Scan for Additional Codes: Use a scanner to check for other diagnostic trouble codes that may indicate related issues. Consult Technical Service Bulletins: Look for any manufacturer TSBs that might apply to the specific issue. Replace Faulty Components: Replace any faulty MDS solenoids, valve lifters, or other identified defective parts. Clear Codes and Test Drive: After repairs, clear the codes and perform a test drive to ensure the issue is resolved.

How to fix P3401 – learn from mechanics

I looked into P3401 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Jeep

Vehicle Information:
2008 Jeep Commander Overland 5.7L

Issue + Repair History:

• Occasional misfire at idle, worse during acceleration.
• Can run well for 5-10 miles.
• Multiple misfires noted, #6 cylinder worst.
• MDS circuit codes set even when MDS not active.
• Misfires persist with MDS disconnected.
• Intake removed to check for rodent damage, solenoids Ohmed out, grounds and harness checked.
• History “fuzzy” after purchase from a new/used car dealer.

Other OBD2 Codes + Test Results:

• P0300: multiple misfire.
• P3449, P3441, P3425, P3401: MDS solenoid circuit.

Suggestions to Fix Issue:

• Check if using correct OE plugs; avoid aftermarket plugs.
• Possible lifter issues.
• Back probing the MDS circuit on a test drive to see if misfire coincides with activation.
• Scope out ignition/injector circuits.

Final Fix:

• New coils fixed the issue, following advice from STAR about a radio interference condition. MDS codes were set without setting a misfire. Coils swapped to verify repair.

Case #2: Chevrolet

Vehicle Information:
2007 Chevrolet Avalanche LTZ 5.3L

Issue + Repair History:

• Misfire on cylinder No. 4, checked spark, fuel compression, OK.
• No. 4 lifter had a broken pin; replaced all variable lifters, head gaskets, pressure relief valve, and baffle for valve per GM dealer’s recommendations. Installed synthetic oil.
• After repairs, engine started well but had low power and check engine light on during test drive with codes for lifters inactive.

Other OBD2 Codes + Test Results:

• P3401, P3425, P3441, P3449: Lifters inactive.

Suggestions to Fix Issue:

• Check if lifters installed correctly and not turned around.
• Inspect oil condition, active fuel management passage plate for debris or carbon, and electrical concerns in plate assembly.
• Verify VLOM assembly connector is plugged in and not damaged, check fuse ENG in fuse block.
• Check fuse 4 (ENG) in underhood fuse box for electrical issues affecting all 4 lifters simultaneously.
• Consider if VLOM seals are intact; a crack can cause loss of oil pressure to lifters.

Final Fix:

• Replaced valve lifter oil manifold (VLOM) after ensuring all wiring and connections were intact and undamaged. New VLOM installation resolved the issue, ensuring active lifters operated correctly. Customer expressed gratitude with a gesture at a local bar.

Case #3: Dodge

Vehicle Information:
2008 Dodge Charger R/T 5.7L

Issue + Repair History:

• Stalling, ASD and fuel pump relay clicking, #7 injector missing a pulse.
• Ground from ECM to ASD relay spiking on and off.
• Cam and crank signals good.
• At 1500 rpm, runs fine.
• Swapped computer with programmed VIN, issue persists.
• Voltage dropping to 4 volts traced to ASD relay clicking.
• Checked wires from TIPM to rear fuse block, alternator, cam sensor, crank sensor, ohmed coils, injectors.
• Considered ignition switch as potential cause.

Other OBD2 Codes + Test Results:

• P3449: Cylinder 7 deactivation control circuit.
• P3441: Cylinder 6 deactivation control circuit.
• P3425: Cylinder 4 deactivation control circuit.
• P3401: Cylinder 1 deactivation control circuit.
• P0688: Auto Shutdown relay sense circuit.

Suggestions to Fix Issue:

• Check system voltages at ignition switch, ECM, and fuse box.
• Inspect TIPM and spark plugs for aftermarket or wrong type.
• Look into wiring to oil control solenoids for MDS systems under the intake manifold.
• Consider voltage drop as indication of resistance in the circuit; inspect for bad circuit or load.

Final Fix:

• Identified problem was coil #8 causing ASD relay clicking and voltage spikes over 20 volts.
• Unplugging coil #8 stopped the ASD relay clicking and voltage spikes, resolving the issue.

Case #4: Jeep

Vehicle Information:
2007 Jeep Grand Cherokee Limited 5.7L

Issue + Repair History:

• Running on only 4 cylinders with all 4 MDS sensor codes.
• Dealer actions: Reflash per TSB, replaced PCM under warranty, replaced all 4 MDS sensors, hardwired MDS solenoids.
• Considered complete engine harness replacement; customer declined.
• Question about potential lifter problems and necessity to remove heads for replacement.

Other OBD2 Codes + Test Results:

• P3449, P3441, P3401, P3425: MDS codes for cylinders 1, 6, 7, 4.

Suggestions to Fix Issue:

• MDS solenoids issue likely electrical, not lifters. Check common ground for MDS solenoids.
• Ensure proper oil type, consider 20w-50, and check for broken valve springs.
• Possible wire harness issues post PCM flash. A battery disconnect for an hour may resolve.
• Check ground circuit Z42 BK/LG 20ga. to splice S154 and connector C112 at left rear of engine.

Final Fix:

• Repaired harness dealer had hardwired. Found ASD relay toggling due to #2 coil with high secondary resistance causing feedback and PCM shutdown.
• Replacing coil resolved MDS light and running issues, returning vehicle to normal operation.

Case #5: RAM

Vehicle Information:
2014 Ram 2500 Tradesman 6.4L

Issue + Repair History:

• Wire loom from PCM to engine and transmission needed replacement.
• Previous attempted repairs by someone with limited knowledge.
• Motor mount bolts left loose, wire ends damaged, PCM connectors destroyed.
• MDS solenoids removed and block-off plugs installed, leading to low voltage and injector codes.
• Both locking connectors at PCM unable to lock properly.

Other Test Results:

• Codes: P3401, P3425, P3441, P3445 (open circuit, MDS solenoids had been removed and replaced).
• Low charge volt, bypass control alternator charged, voltage weak from PCM.
• P0201 (Cyl1 injector control circuit), injector will pulse with injector driver, noid light causes P0202 code.
• Injector control tested with noid light – pulse was dim and set P0202 code.

Suggestions to Fix Issue:

• Examine RF hub, BCM, ECM for damage due to short in body wiring harness.
• Inspect for shorts behind front driver wheel well and on engine wiring harness passenger side.
• Check AR fuse locations in PDC for suspicious readings.
• Consider connector repair kits from the dealer as a cheaper alternative to replacing the entire harness.

Final Fix:

• Repaired the harness that was previously hardwired for MDS solenoids.
• Discovered ASD relay toggling caused by a #2 coil with high secondary resistance, leading to PCM shutdown.
• Replacing the coil resolved the issue, eliminating MDS light and running problems.
• Major job, approximately 40 hours of work, but customer was satisfied despite the expense.

Advice	Brief Description of Diagnostic Step
Check all related wiring and connectors	Inspect for damaged, loose, or corroded connectors and wiring, especially at the PCM and affected components.
Inspect the MDS solenoids and related components	Verify the operation and condition of MDS solenoids, and replace if necessary.
Ensure proper grounding of affected circuits	Check ground connections for the MDS system and other related circuits for integrity.
Test for voltage drops and shorts in the circuit	Use a multimeter to check for voltage drops and shorts that could affect the circuit’s functionality.
Consider the impact of aftermarket or incorrect parts	Make sure that all parts, especially spark plugs and coils, are OEM or specified for the vehicle to avoid compatibility issues.
Replace damaged coils if necessary	If a coil is found to have high secondary resistance or is damaged, replace it to resolve misfires and related codes.
Verify PCM and software are up to date	Ensure the PCM has the latest software updates to prevent software-related issues causing the fault.
Check for physical damage to the wire harness	Inspect the wire harness for any physical damage, chafing, or breaks, especially near heat sources and moving parts.
Ensure the use of proper oil type	Confirm that the correct oil type is used, as incorrect oil can affect MDS operation.
Disconnect the battery to reset the system	In some cases, disconnecting the battery for a short period may reset the system and clear temporary electronic glitches.