Chat with one of our friendly reps to get help quick.

Something on your mind not found here? E-mail us.

We offer phone support if you don't want to type.

Support Center

P4 Error Code: Outdoor Unit High Discharge Temperature ProtectionNote:&#xA0;Diamante wall-mounted systems have a different troubleshooting procedure for this error code than Quantum wall-mounted systems. For that procedure, read this <a href="https://help.pioneerminisplit.com/en-US/p4-error-code-diamante-3340565" target="_blank" rel="noopener noreferrer">article</a>.&#xA0;<h2 id><img src="https://attachments.gorgias.help/Q9r0k7BYaV2vg13y/hc/9JWjXVxG8m6DvMqm/2026101316-18d3f9d0-0501-4ebe-9688-6c650fd3d992-p4_code.png" style="width: 800px;" class="fr-fic fr-dib fr-bordered"> </h2>

This code indicates that the outdoor unit’s high discharge temperature protection has been activated. This article applies to Quantum wall-mounted systems.

P4 Error Code (Quantum Series)

Troubleshooting

By Error Code

Diamante & Quantum Systems

Wall-Mounted Systems

Pioneer Offers Hyper-Heat Units

Pioneer Systems Offer Both Heating & Cooling Functions

Understanding the Difference Between 115V & 230V Systems

Understanding the Refrigerants Used for Each Model

How to Choose a System

Does Pioneer Offer Pre-Charged Linesets?

Does Pioneer Offer Pre-Flared Linesets?

How Mini-Splits Are Powered

Multi-Zone Explained

Pioneer Mini-Splits Function as Dehumidifiers

Pioneer Offers Various Lineset Lengths

Pioneer Systems Feature Factory Pre-Charged Refrigerant

Running a Mini-Split Below Its Total Zone Capacity

Single-Zone Mini Splits Cannot Be Used with Multiple Indoor Units

Understanding the Allowable Zone Combinations for Multi-Zone Systems

Understanding the Life Expectancy of Pioneer Systems

Mini-Split Basics

Determining the Unit Size Needed for Your Space

How System Sizing Causes Short Cycling

Matching the Lineset Diameter to Your Pioneer Indoor Unit

Sizing & Efficiency Guide

Start Here

Identifying Energy Star-Certified Equipment

Understanding the Differences Between Inverter+ & Inverter++ Systems

Understanding the Differences in Wall-Mounted Mini Split Systems

Compare Models

Claiming Energy Star Tax Credits for Pioneer Systems

Managing Multiple Credit Card Charges

Redeeming Your Pioneer Rewards Points Online

Understanding Your Discount Options

Why Your Pioneer Discount Code Says "SAMPLE"

Financing & Payment

How to Qualify for Free Shipping

Understanding Our Shipping & Delivery Details

Order Status & Shipping

Diamante Essenza High-Wall (WYT-17) Overview

Diamante Essenza High-Wall (WYT-20U) Overview

Diamante Pro High-Wall (WYT-20S) Overview

Quantum Fresh High-Wall (WYT-FA) Overview

Quantum Hyperformance High-Wall (WYT-25) Overview

Quantum Ultra 4-Way Ceiling Cassette (CYB-20) Overview

Quantum Ultra 8-Way Ceiling Cassette (CYT-24) Overview

Quantum Ultra Ducted Ceiling Concealed (RYB-20) Overview

Quantum Ultra Ducted Ceiling Concealed (RYT-24) Overview

Quantum Ultra Floor-Ceiling Flex (UYB-20) Overview

Quantum Ultra Floor-Ceiling Flex (UYT-24) Overview

Quantum Ultra Floor/Low-Wall Mounted Console (FYB-20) Overview

Quantum Ultra High-Wall (WYT-24) Overview

Quantum Ultra Multi-Zone (YNL-24) Overview

Quantum Ultra Single-Way Ceiling Cassette (CYK-24) Overview

Vertex Ducted Central Split (DYC-18) Overview

Ducted & Ductless Systems

ECOasis 50 Ductless Wall-Mounted Single-Room Energy Recovery Ventilator (ERV) Overview

ECOasis 150 Ductless Wall-Mounted Single-Room Energy Recovery Ventilator (ERV) Overview

Energy Recovery Ventilators

QHD070 Whole-House Ducted Dehumidifier (QHD) Overview

High Performance Dehumidifier

Full Inverter Rooftop RV Air Conditioner Heat Pump (PYZ) Overview

Under-Bench RV Inverter Packaged Heat Pump Air Conditioner (PYR) Overview

Recreational Vehicle Systems

Product Line Overviews

Find Out How to Complete Returns

Figure Out How to Start Your Return

Learn About Our Policy for Undeliverable or Refused Shipments

Learn About Our Return Policy

Understand How to Return an Item

Understand the Eligibility Requirements for Refunds

Understand Our Return Fees

Understand Our Return Process

Returns & Refunds

Shopping & Pre-Purchase

Can I Install the System Myself?

Estimating System Installation Costs & Time

Locating an Installer for Your System

First-Time Installations

Can Wall-Mounted Indoor Units Be Installed on the Ceiling Instead?

Does the Indoor Unit Need Additional Hardware for Wall Mounting?

General Installation FAQ

Conducting Test Runs

Connecting the Refrigerant Piping

Drilling Requirements for Installing Drain & Refrigerant Lines

Evacuating the Refrigerant Circuit

Selecting the Correct Standard Wire Gauge for Connections

Understanding the Differences Between a 6-Foot Plastic Whip & a 4-Lead Wire

Understanding the Ideal Mounting Height for Indoor Units

Understanding Refrigerant Lineset Installation

Understanding the Requirements for Installing Wall-Mounted Systems

Drainage Tests

Installation Basics

Ceiling Cassettes

Ducted Ceiling Concealed

Ducted Central Split

Floor/Ceiling/Low-Wall Flex Consoles

Floor/Low-Wall Mounted Consoles

Wall-Mounted Units

Indoor Units

Installing Outdoor Units: Getting Started

Selecting the Installation Location for Outdoor Units

Installing the Drain Joint for Outdoor Units

Mounting the Outdoor Unit

Installing the Condensate Drain Hose for Outdoor Units

Outdoor Units

Ductless & Ducted Systems

Installing ECOasis 50 Energy Recovery Ventilators

Installing ECOasis 150 Energy Recover Ventilators

Energy Recovery Ventilator

Connecting the Drain Fitting for QHD070 Whole-House Ducted Dehumidifiers

High Performance Dehumidifiers

Installing Rooftop RV Systems: Getting Started

Understanding the Installation Requirements for Rooftop RV Systems

Creating the Roof Opening for Rooftop RV Systems

Placing the Unit onto the Roof for Rooftop RV Systems

Installing the Air Duct & Top Mounting Plate for Rooftop RV Systems

Setting Up the Electrical Wiring for Rooftop RV Systems

Setting Up the System Connections for Rooftop RV Systems

Mounting the Panel for Rooftop RV Systems

Rooftop RV Inverter

Installing Under-Bench RV Systems: Getting Started

Understanding the Installation Requirements for Under-Bench RV Systems

Creating the Floor Openings for Under-Bench RV Systems

Securing the Under-Bench RV System into Place

Installing the Wall Thermostat for Under-Bench RV Systems

Creating the Recirculation Air Opening for Under-Bench RV Systems

Understanding the Ductwork Best Practices for Under-Bench RV Systems

Connecting & Powering Up Under-Bench RV Systems

Under-Bench RV Inverter

Installation

Understand the DIP Switches for Vertex Ducted Central Split Systems

DIP Switch Layouts

Turn the LED Display On or Off

Understand the Display Board for Ducted Ceiling Concealed Systems

Understand the Display Panel for Rooftop RV Systems

Understand the Front Panel Displays for Eight-Way Ceiling Cassette Systems

Understand the Front Panel Display for Universal Floor-Ceiling Flex Systems

Understand the Front Panel Display for Wall-Mounted Systems

Understand the Master Unit Display for ECOasis 50 Energy Recovery Ventilators

Understand the Onboard Controller & Terminal Block Layout for QHD070 Whole-House Ducted Dehumidifiers

Understand the Wall Controller Display for RV Under-Bench Systems

Display Layouts

Clean the Filters for 4-Way & 8-Way Ceiling Cassette Systems

Clean the Filters for Diamante Wall-Mounted Systems

Clean the Filters for Floor/Low-Wall Mounted Systems

Clean the Filters for Quantum Fresh High-Wall Systems

Clean the Filters for Quantum Ultra Ducted Ceiling Concealed Systems

Clean the Filters for Quantum Ultra Universal Floor-Ceiling Flex Systems

Clean the Filters for Quantum Ultra & Hyperformance High-Wall Systems

Clean the Filter Screen for Rooftop RV Systems

Clean the Filters for Single-Way Ceiling Cassette Systems

Clean the Filters for Under-Bench RV Systems

Filter Cleaning & CL Code

Activate Auto Mode

Activate the Child-Lock Function

Activate Cooling Mode

Activate Dry Mode

Activate Energy Saver (ECO) Mode

Activate Fan-Only Mode

Activate the Fresh Air Feature for Quantum Fresh High-Wall Systems

Activate Gentle Wind Mode for Quantum Fresh High-Wall Systems

Activate Heating Mode

Activate the I Feel Feature

Activate the Memory Feature

Activate Mute Mode

Activate the Self-Clean Feature

Activate Sleep Mode

Activate the Timer On/Timer Off Function

Activate Turbo Mode

Activate 46°F Freeze Protection

Understand the Auto-Restart Feature

Understand the Voice Control Feature For Quantum Fresh High-Wall Systems

Understand the Defrost Function

Understand the Dehumidification Function

Understand the Drainage Functions

QHD070 Whole-House Dehumidifiers

Activate Dehumidification Mode

Activate Night Mode

Activate Ventilation Mode

Rooftop RV Systems

Under-Bench RV Systems

Activate the Accelerated Cooling/Heating Function

Understand the Anti-Cold Air Function

Understand the Compressor Crankshaft Heater Control Function

Understand the Heating Fan Delay Function

Understand the Indoor Coil Anti-Freezing Function

Understand the Passive Dehumidification Function

Understand the Refrigerant Leak Detection Function

Vertex Ducted Central Split Systems

Functions & Modes Explained

Determine the Breaker Size & Wire Needed for Your System

Diagnose & Prevent Crossed Wiring in Multi-Zone Systems

Understand how the System Receives Power

Electrical Related Queries

Maintenance Tips

Operation & Usage

P4 Error Code (Quantum Series)Updated 13 days ago