What Is The Diagnostic Code SPN 4357 FMI 5? (Freightliner)

You may be the lucky one and get one of those rare codes that only pop up once in a blue moon. The lack of available information only means that you have to go to a mechanic or a dealer to get the proper diagnosis. It happens from time to time.

This code stands for - Scr Line Heater #4 Circuit Failed Open and Scr Line Heater #4 Circuit Failed Open: Aftertreatment 1 Diesel Exhaust Fluid Line Heater 4 Current Below Normal Or Open Circuit; Open Load On Function "am_pwm_line_heating_4". Both sound more complicated than they really are.

To learn more about this fault code just continue to read our article. It will have the best information possible so you can make the best repair in a short amount of time. Getting everything back to normal is the goal of any repair.

Diagnostic Code SPN 4357 FMI 5


When you see this code pop up on your screen do not be alarmed. From what we have been able to tell, there does not seem to be any performance issues or threat of derating.

According to the official SPN code list, this code represents an open circuit in your line heater. The repair will depend on what other codes are set at the same time.

The good news is that there should be only 6 steps to take if you do not resolve the problem sooner than that. There may only be 2 other fault codes that may be present when you attach your code reader.

Only two are mentioned in the data sheets. The first will be SPN 4355 FMI 5 and that code is telling you that you have an open circuit in Line heater #2. If you have these two codes, then the following work needs to be done:

repair open between pin 15 of the ACM2.1 120-pin connector

and pin 2 of line heaters 2 and 4.” That is all there is to it unless you only see SPN 4357 FMI 5. If that is the sole code, then you move on to the following 5 steps.

If SPN 4356 FMI 5 is Set


The other code that may appear with SPN 4357 FMI 5 is SPN 4356 FMI 5 and that code stands for - Scr Line Heater #3 Circuit Failed Open. The repair is going to be similar to the previous repair with one minor difference.

Instead of repairing heaters 2 & 4, you will be repairing the #2 pin of line heaters 3 & 4. You need to be careful as even these slight differences can cause some mistakes to be made.

Having two codes appear usually makes this repair easier as you only have one step. The more difficult repair will be when only the SPN 4357 FMI 5 code appears. Those steps are coming up.

Steps For SPN 4357 FMI 5 Repair


If you only have one code, then the first step to take would be to disconnect line heater #4. Then turn the key to the on position but leave the engine off.

The other steps are as follows:

4. Measure the voltage between pin 2 on the harness side of line heater 4 connectors and ground.

a. If the voltage is greater than 11.75, Go to step 5.

b. If the voltage is less than 11.75, repair the wire between pin 2 on the harness side of the line heater 4 connector and pin 15 of the ACM2.1.

5. Measure the voltage between pin 1 on the harness side of the line heater 4 connector and ground.

a. If the voltage is between 2.25 and 2.50, Go to step 6.

b. If the voltage is not between 2.25 and 2.50, repair the wire between pin 1 on the harness side of the line heater 4 connector and pin 32 of the ACM2.1.

6. Measure the resistance on the heating element side of the line heater 4. If resistance is not within this range, replace the line

heating element.” (source)

If you still see the code after completing those steps, double-check your work or go to an experienced mechanic to see if something else is wrong.

Diesel Exhaust Fluid Line Heater Resistance Chart

This table provides you with the proper resistance values.

Length in inches Nominal Resistance in ohms Minimum resistance in ohms Maximum resistance in ohms
19.6 16 12.8 19.2
39.3 9.8 7.84 11.76
47.2 8.6 6.88 10.32
55.1 7.8 6.24 9.36
62.9 7 5.6 8.4
70.8 6.1 4.88 7.32
78.7 5.6 4.48 6.72
86.6 5.2 4.16 6.24
94.4 4.9 3.92 5.88
102.3 4.6 3.68 5.52

The source from this table is the same link above. This is a simple repair that you should be able to do it yourself.

A Color-Coded Fault List

Light blue- Rationality Fault

This may make your repair work even easier. The list we are about to link to is color coded with the legend at the top for easier understanding. There are 6 colors used to identify the exact type of problem you are experiencing.

These categories are- Yellow- Circuit Fault

Light blue- Rationality Fault

Red- Engine Protection Fault

Orange- Component Broadcasted Fault

Purple- Communication Data Fault

Light green- Information Fault

Knowing which type of problem you are facing helps you gather your tools faster and be ready for the type of repair you need to make. There are 24 pages of SPN FMI fault codes and on page 25 you will get a little more information to help you.

Just click here to get to this unique but very handy color-coded fault code list.

Some Final Words

It is possible that you may not see this code triggered any time soon or at all. It is not one that is talked about very often and the repair is fairly simple. There should be no impact on engine performance when you see this code but do not delay in getting it fixed. It could get worse if you ignore it.

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