P3425 Code: Cylinder 4 Deactivation Control Circuit/Open
P3425: Prove the Electrical Fault Before Mechanical Work
Locate cylinder 4 and separate its deactivation control circuit from lifter, oil-pressure and misfire problems.
DIAGNOSTIC FOCUS
- FAULT TYPE
- Cylinder 4 deactivation/intake valve control
- FIRST CHECKS
- Cylinder numbering, shared power and driver/coil integrity
The code concerns cylinder 4 electrical control; it does not prove that a lifter has collapsed.
P3425 means Cylinder 4 Deactivation/Intake Valve Control Circuit/Open. The controller identified an integrity concern in the cylinder 4 deactivation/intake-valve control circuit. The generic wording includes circuit/open, while the exact monitored fault grouping depends on the engine and controller. This is cylinder 4, not cylinder 3, and the code alone does not diagnose a mechanical lifter failure.
Save the complete code set, identify cylinder 4 from the engine numbering diagram and inspect the relevant circuit and shared supplies. Treat oil-pressure warnings or major mechanical symptoms as separate stop conditions.
What Does the P3425 Code Mean?
Cylinder-deactivation systems command hardware that changes selected cylinders' operation under permitted conditions. Their electrical integrity monitors check whether the output circuit behaves as expected. A disconnected actuator, wiring defect, shared-feed problem or coil fault can therefore generate an electrical code without proving that the internal valve train has mechanically failed.
GM's 2018 OBDG03A LT4 summary describes an open-circuit driver-voltage test while the output is off. GM's 2010 OBDG07 table groups command-versus-circuit mismatch across open/short conditions. This shows why a universal continuity-only or voltage threshold is inappropriate.
Circuit diagnosis and mechanical diagnosis can overlap, but they must not be collapsed into one conclusion. Low oil pressure, abnormal noise and a misfire require attention in their own right. Conversely, finding an acceptable oil level does not prove a control wire or coil is sound. Establish which evidence supports each branch before selecting a repair.
Use the physical cylinder-numbering diagram, not the fourth firing event or a generic bank assumption. Locate the actual deactivation actuator and its wiring.
Several cylinder-control codes can point toward a common supply or connector. One code may instead need a focused branch test; neither pattern proves a component by itself.
The controller may test circuit behavior with the output off or under a specified command. An unqualified voltage reading at the wrong state can be misleading.
P3425 Symptoms, Severity, and Driving Safety
The electrical monitor may detect a fault even when the engine appears to run normally. Preserve the record before clearing it.
The controller may limit cylinder-deactivation operation when a relevant fault is present. That response does not prove a particular lifter or solenoid is damaged.
Record the affected cylinder and companion misfire codes. An electrical deactivation code does not eliminate ignition, fuel or mechanical explanations for roughness.
Stop and address this warning according to the vehicle's instructions. An oil-pressure concern is not a condition to reproduce while diagnosing the control circuit.
Severe new noise calls for stopping and qualified inspection. Do not keep running to obtain a cleaner scan trace.
Recent disconnection, routing changes or assembly work makes connector identity and shared feeds important early checks.
Diagnose the control circuit promptly; oil-pressure warning, severe noise or a flashing MIL requires stopping.
P3425 Causes and the Evidence That Separates Them
The first four branches establish the electrical path. Mechanical symptoms and controller decisions must then be evaluated on their own evidence, without treating every deactivation code as the same engine repair.
Open or damaged control wiring
A broken conductor or poor terminal can interrupt the cylinder 4 control path.
How to prove it: Use the specified isolation test and inspect the harness at relevant connector and routing points.
Check firstShared supply defect
A common feed or connector can affect more than one deactivation channel.
How to prove it: Compare companion codes and test the actual shared supply under the approved conditions.
Check firstActuator coil fault
The relevant coil may fail its electrical test even when surrounding wiring is intact.
How to prove it: Test it only as isolated and specified by the OEM, using the correct limits for that part.
Verify directlyShort or incorrect circuit state
Some application fault groupings include command-to-state mismatches beyond a simple open conductor.
How to prove it: Use the exact controller's decision tree rather than stopping after a continuity check.
Verify directlyInternal driver concern
A control module may fail to switch or monitor a circuit after external paths are proven good.
How to prove it: Establish supply, wiring and actuator integrity before a protected driver test or module replacement.
Verify directlySeparate mechanical or oil-path problem
Noise, misfire or oil-pressure evidence may justify a parallel mechanical investigation.
How to prove it: Document that evidence independently; do not infer collapsed lifters from the circuit code alone.
Final branchManufacturer examples use different driver states and fault groupings. No universal coil resistance or control-wire voltage is supplied here.
Using MA200 Plus During P3425 Diagnosis
The iCARZONE MA200 Plus provides full-system scanning, available freeze frame/live data and reports. For P3425, preserve cylinder-deactivation records, available command data and related circuit faults before clearing or disconnecting anything.
Module access, active tests and service functions vary by VIN, ECU and software. Confirm the exact cylinder-4 driver or actuator test for the engine. General active-test support does not guarantee a deactivation routine or identify the physical cylinder.
A meter and the specified circuit tests must prove the feed, coil and control path. Mechanical or oil-pressure testing requires separate equipment when justified; scan data cannot prove lifter condition.
iCARZONE MA200 Plus Multi-System OBD2 Diagnostic Scanner
Preserve cylinder-deactivation records, available command data and related circuit faults; confirm coverage before any active test.
Checked September 8, 2026: MA200 Plus was $144.99 USD (compare-at $179.99). Confirm current pricing and VIN coverage before purchase.
How to Diagnose P3425 in 6 Steps
Begin by mapping the code to the correct cylinder, actuator and controller output. Then test common supplies and the individual electrical path in the order prescribed for that engine before escalating to internal components.
P3425 Quick Diagnostic Path
-
1
Record individual and shared fault patterns
- Save all codes and identify whether faults affect cylinder4 alone or a shared deactivation group.
- Include whether the MIL is flashing and whether noise or oil-pressure warnings appeared. Avoid clearing related codes that could distinguish a shared feed problem from a single cylinder-control branch.
-
2
Map cylinder 4 and the installed system
- Confirm engine/cylinder numbering and the installed deactivation system.
- Cylinder numbering is a physical engine convention, not a firing-order index. Confirm the actuator's actual location and connector assignment before ordering a part or unplugging a harness.
-
3
Inspect wiring and separate safety concerns
- Inspect oil level safely, but also inspect relevant connectors, harness and shared supplies for the actual circuit record.
- Check oil level only by the safe owner-manual method, while recognizing that this does not test oil pressure or an electrical circuit. Inspect the applicable connector, harness routing and shared power path separately.
-
4
Test the isolated control circuit
- Test cylinder4 control wiring and actuator coil under the OEM isolation and power-state instructions.
- Read the specified power and connector states before checking continuity or coil resistance. A circuit can appear continuous yet fail under its operating conditions; use the OEM tests to distinguish those situations.
-
5
Distinguish driver from mechanical findings
- Use approved driver testing to distinguish coil, supply, harness and module; investigate mechanical/oil-path faults only where supported.
- A controller diagnosis requires proven external circuits and a permitted driver test. A lifter or oil-path diagnosis requires its own mechanical evidence, particularly if a separate misfire or noise persists after the electrical repair.
-
6
Verify the repaired electrical path
- Repair confirmed faults, perform required setup and verify circuit diagnostics and normal operation.
- Complete required setup and the relevant circuit-monitor verification. If mechanical symptoms remain, do not call the vehicle repaired solely because P3425 is absent; document and resolve the remaining fault separately.
How to Fix P3425 and Verify the Repair
Repair the proven harness or terminal
Restore the cylinder 4 control path with the approved materials and routing. Verify terminal fit and the circuit under the specified test state.
Restore a shared feed
Repair a confirmed power or connector defect affecting the deactivation group. Recheck every related circuit rather than assuming one cleared code proves all channels.
Replace an electrically failed actuator
Use the correct part only after its coil or other permitted test proves failure. Complete installation and setup without treating the new part as a substitute for wiring verification.
Follow the evidenced advanced branch
Escalate to a protected module test or mechanical/oil-path investigation only when prior tests justify it. Keep separate findings and repair recommendations clear.
Electrical diagnosis
VIN-specific quoteAsk whether the quote includes cylinder identification, shared-feed testing and isolation of the coil, harness and driver.
Harness or feed repair
VIN-specific quoteThe location and extent of damage determine cost. A repairable terminal should not automatically become a complete engine-hardware estimate.
Actuator access and installation
VIN-specific quoteAn integrated or difficult-to-access assembly can change labor scope. Require the electrical finding that supports the proposed replacement.
Mechanical or module work
VIN-specific quoteThese branches need independent proof and an itemized estimate. A P3425 printout alone is insufficient justification for lifter or controller replacement.
An oil change may be relevant to a documented maintenance or oil-condition problem, but it is not proof that an open control circuit has been repaired.
Do not apply a software deactivation delete as the diagnostic answer. It can suppress operation without correcting the underlying electrical or mechanical issue.
P3425 OEM Differences and DIY Limits
GM's published diagnostic tables show that the monitor's output state and fault grouping vary. They support a circuit-first investigation while cautioning against one universal meter reading.
The GM 2018 OBDG03A summary describes an open-circuit driver-voltage check while the output is off. Its enable conditions and thresholds belong to that controller.
The GM 2010 OBDG07 table includes command-versus-circuit mismatch across open/short states. A continuity-only interpretation may therefore be incomplete for a different application.
Neither source proves that a cylinder 4 lifter has collapsed. Apply the relevant circuit tests and investigate mechanical concerns only when the vehicle supplies supporting evidence.
GM's 2018 OBDG03A LT4 summary describes an open-circuit driver-voltage test while the output is off. GM's 2010 OBDG07 table groups command-versus-circuit mismatch across open/short conditions. This shows why a universal continuity-only or voltage threshold is inappropriate.
- Save the complete accessible engine fault set.
- Record oil-pressure warnings, noise and whether the MIL flashes.
- Confirm engine identity and recent service details.
- Perform only safe owner-manual oil-level and visual checks.
- Do not continue running with severe noise or oil-pressure warning.
- Do not power ECM pins or an unknown actuator directly.
- Do not use firing order to locate cylinder 4.
- Do not authorize a mechanical repair solely from the circuit code.
Frequently Asked Questions About P3425
Is P3425 for cylinder 3 or cylinder 4?
Does P3425 prove a collapsed lifter?
Can low oil explain P3425?
Why check other cylinder codes alongside P3425?
Can MA200 Plus command deactivation?
Can I use one universal resistance value?
Can I keep driving with P3425?
What confirms a successful P3425 repair?
Sources and Technical Review Notes
- Diagnostic Trouble Codes (DTC) List — Generic DTC definition only; not vehicle-specific test limits or repair verdict.
- GM 2018 OBDG03A Engine Diagnostics, LT4 Unique Summary — Cylinder4 deactivation open-circuit driver monitor; controller-specific thresholds and enable states.
- GM 2010 OBDG07 Engine Diagnostics — Cylinder4 electrical integrity and command/state mismatch; grouped open/short architecture differs from later example.
- Tags: DTC iCARZONE MA200 Plus OBD-II P3425
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