ISO/SAE Reserved Codes: What Do They Mean?

Have you ever experienced the frustration of driving your car when suddenly it begins to run rough and perform poorly? 

In some cases, you may turn to an On-Board Diagnostics (OBD) scanner or get a mechanic to do so, but instead of the typical combination of letters and numbers, you receive a puzzling message: “ISO/SAE Reserved.” Don’t worry. This is the problem many people relate to. 

Get ready to learn everything you need to know about the mysterious ISO/SAE Reserved code – from its symptoms and causes to diagnosis and severity – in this comprehensive article.

What Does ISO/SAE Reserved Code Mean?

What are ISO and SAE?

Before getting into what ISO/SAE Reserved really is, it’s a good idea to go through the definitions of the two constituents: The International Standard of Organization (ISO) and the Society of Automotive Engineers (SAE).

These two regulatory bodies are responsible for developing standards in the automotive and aerospace industries. First, SAE International was founded in 1905. It is a US-based organization that focuses on developing standards in the mentioned industries.

ISO was established in 1947 with the aim of promoting international trade in goods and services. This institution implements a system of uniformity in scientific, intellectual, technological, and economic strategies.

How Do These Organizations Relate to the OBD Code?

Since late 1995, car manufacturers with these regulatory bodies have worked together to develop a set of compulsory guidelines to ensure the reliability and timeliness of message delivery in vehicle onboard diagnostic systems and serial data communication. These guidelines encompass a range of other factors. These include the reduction of contradictory information, optimization of expenses, and mitigation of electromagnetic interference. Manufacturers can maintain high-performance standards by complying with these guidelines and ensuring their vehicles operate efficiently and safely.

If you receive the “ISO/SAE Reserved” code on your OBD scanner, it doesn’t necessarily mean a problem with any specific part or component of your vehicle. Rather, it indicates that the system violates particular standards the ISO and SAE regulatory bodies set. This could be due to various reasons, such as a malfunctioning sensor, a software glitch, or an issue with the communication system itself.

Thus, it’s crucial to diagnose and solve the problem correctly. By doing this, you may be confident that your car is running within the established standards and avoid future issues.

Many fundamental protocols in the automotive industry were enacted by ISO, including the Controller Area Network (CAN) bus, the DC bus, the keyword protocol, the Local Interconnected Network (LIN), and the Vehicle Area Network (VAN).

In the scope of this article, we’ll concentrate on the CAN bus only. It is a complex network of wires and connectors that allows the Powertrain Control Module (PCM) and other onboard controllers to communicate quickly and simultaneously with each other. With up to seventy onboard controllers in a single vehicle, the CAN bus is critical for ensuring proper communication between components.

Suppose the PCM detects an interface error in one of the controllers or the CAN, indicating a violation of ISO/SAE guidelines. In that case, it will store an error code and may illuminate the malfunction indicator lamp.

What Are The Symptoms Of These Codes?

While an ISO/SAE Reserved code itself does not indicate a specific problem or failure in the vehicle, it can still cause symptoms such as a Check Engine Light, rough idle, or poor performance. In some cases, it may not cause any symptoms at all. Additionally, it’s important to note that this code can also appear alongside other diagnostic trouble codes.

What Are The Potential Causes Of These Codes?

There are some causes of this type of trouble code:

  • Wiring and connector issues
  • Malfunctioning controller
  • Controller programming error
  • Problems with sensors or actuators

How Serious Are These Codes?

The conditions that trigger an ISO/SAE reserved code can vary from significant issues to minor inconveniences, making this system potentially frustrating.

How Can You Fix These Code?

Before diving into the diagnostic process for an ISO/SAE reserved code, it’s important to scan and repair any other stored codes first.

Checking Technical Service Bulletins (TSBs) that match your car’s symptoms and codes can also make the repair process more manageable. To prevent ISO/SAE codes, it’s crucial to keep your car in good shape by removing any battery corrosion, ensuring a full battery charge, and verifying that the alternator is charging adequately.

Additionally, visually inspecting all wiring and connectors is advisable, as rodents such as rats can cause damage. Once the inspection is complete, use a scanner to retrieve all stored codes and freeze frame data. The OBD2 scanner can provide you with crucial clues for diagnosing the issue.

After clearing the codes, a test drive is necessary to ensure that the code is not intermittent. If the code is reset, perform a wiggle test on all controller/CAN bus connectors to detect any potential defects or programming errors. In the absence of helpful TSB entries, suspecting a controller defect or programming error may be necessary.

Check This Infographic About ISO/SAE Reserved Code


We’ve collected a comprehensive list of all ISO/SAE Reserved codes. Check out the file below for a free download.

Reference Sources

What Does ISO/SAE Reserved Mean?

On-board Diagnostics – Wikipedia

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