What-Is-Freightliner-Fault-Code-SPN-3597-FMI-4-(FMI 2)

What Is Freightliner Fault Code SPN 3597 FMI 4? (FMI 2)

One thing about fault codes. Unless engine builders go back to the 1960s way of building engines, you will always see a fault code at some point in time. There are too many devices on your engine for none to show up at least once.

There are 4 definitions of this fault code. The best one is- “High Side Digital Output 1 Circuit Failed Low: Ecu Power Output Supply Voltage #1 Voltage Below Normal, Or Shorted To Low Source; Short Circuit To Ground On High Side 1. It is an electrical problem.

To learn more about this fault code, just continue to read our article. It explores the topic so you have the best information possible. Despite the 4 definitions, the steps to fix this issue are not long.

What is The Code 3597 on a Freightliner?


To help clarify this topic so you have a better understanding of where to look for help in solving this code problem, you need to know what brand of engines Freightliner uses in its trucks.

The engines this company uses come from Cummins, Detroit Diesel, Mercedes Benz, and CAT. However, the most common engine you will find in their trucks will be the Detroit Diesel.

What this means is that you can use the official SPN fault code list to know what this and other SPN fault codes mean. The official list won’t give you any repair help, you need to go to the NHTSA.gov data sheets for that information when we do not cover your specific code.

Unless otherwise noted those datasheets are for Detroit Diesel engines, and the official code list for SPN fault codes is for Detroit Diesels, Freightliner, and Cummins. The code definition for Freightliner then are:

- High Side Digital Output 1 Circuit Failed Low

-High Side Digital Output 1 Circuit Failed Low: Ecu Power Output Supply Voltage #1 Voltage Below Normal, Or Shorted To Low Source; Short Circuit To Ground On High Side 1

-Proportional Valve Bank 1 Circuit Failed Low

-Short Circuit To Ground Error At Actuator Relay

As you can see, you are looking for a short, an open circuit, low voltage problems, and other electrical issues. The next problem will be the letters EPA and GHG that follow the FMI code.

While we have not found any explanation for the numbers that follow those letters, those letters may indicate a different repair procedure. In other words, repair procedures for an SPN FMI EPA code may have slight differences from the SPN FMI GHG codes.

Be on the lookout for those letters and any differences in repair instructions. Sometimes you will see a code like this- SPN FMI EPA GHG and those repair instructions may be longer than usual.

SPN 3597 FMI 4


This code is the same as the previous one mentioned. We picked the FMI 4 option even though there are only 3 FMI options listed on the official SPN list. You normally will not find an SPN code on that list without an FMI code following it.

The repair for SPN 3597 FMI 4 EPA 10 is as follows:

1. Disconnect the Diesel Exhaust Fluid (DEF) pump, Pressure Limiting Unit (PLU), diffuser heater, and the DEF injection valve (disregard the additional faults set with components disconnected).

2. Inspect the above component harness connectors for bent, spread, or corroded pins.

a. If pin damage is found, repair as necessary.

b. If no pin damage is found Go to step 3.

3. Turn the ignition ON and clear fault codes. Does the fault become active?

a. Yes; Go to step 4.

b. No; Go to step 7.

4. Turn the ignition OFF (key OFF, engine OFF).

5. Disconnect the Aftertreatment Control Module (ACM2) 120-pin connector.

6. Turn the ignition ON and clear fault codes. Does the fault become active?

a. Yes; replace the ACM2.

b. No; repair harness short to ground between pins 1, 3, or 5 of the ACM2 and pin 2 of the corresponding components.

7. Reconnect the above components one at a time, clearing the fault code after each connection. When a fault becomes active, replace the corresponding component. (source)

The repair instructions for SPN 3597 FMI 4 EPA 10 GHG 14 are at this link. We cannot put them here as they are 3 times as long as the simple EPA 10 instructions.

Cummins Code SPN 3597 FMI 2


We have not come across any information for this code. It is not on the official SPN list of fault codes and that list starts at FMI 3 for SPN 3597. However, when you see this code, the FMI portion is telling you that- Data is erratic, intermittent, or incorrect.

That may mean you have a sensor problem, a communications error, or a faulty module. It is best to talk directly to a qualified mechanic and see if they have had experience with this code.

We did find information on this code for Volvo but a quick check revealed that Volvo does not use Cummins engines in its cars or trucks. But this information may help:

3597-2 Power Supply Lost With Ignition On - Data Erratic, Intermittent, or Incorrect


Supply voltage to the ECM fell below a calibrated limit momentarily, or the ECM was not allowed to power down correctly.” (source) You may experience some level of derating when this code appears.

Also, you may find other fault codes set at this time as well. Make sure to deal with them in the right order.

Some Final Words

Knowing the different fault codes is important. Even if you are not making your own repairs, knowing what they mean will protect you against any unethical mechanic who may try to add more repairs than necessary

Keep up on your codes or have the lists printed out or saved to your favorites so you can look them up without any hassle. Protecting yourself against unethical mechanics is vital.

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