It used to be that you could sit in the engine compartment of your pickup truck and work on the engine. Today, after all the technological upgrades, you are lucky if you can see half the engine. Technology does not make mechanical work easier.
FMI stands for Failure Mode identifier. It is supposed to bring more specific information to help you pinpoint the source of your engine trouble better. Unlike the SPN codes, there are only about 30 of these with many duplicates or reserved definitions.
To learn more about this part of the engine code system, just continue to read our article. It has the information you want to know about so you can understand what your display is trying to say to you. Take a few minutes to see how this important information helps you.
There are several different code identifiers in play these days. One of the more important ones is the FMI or Failure Mode Identifier. As you can see by those terms, this code is supposed to identify the part or mode that has failed on you.
Why it is important is that every, and we mean every, diagnostic trouble code or DTC, has an FMI code attached to it. The ECM is programmed to send out this code every time it detects a problem with one of your engine systems.
The good news here is not that the FMI code provides more specific information about the problem your truck is experiencing. The actual good news is that there are only 30 numbers attached to this code system, not over 50,000 like the SPN system.
The purpose of FMI in diesel engines is to help owners understand and know what is happening when their truck does not work as it should. It is a diagnostic bit of information leading the mechanic to the specific area that has failed.
In other words, it is a monitoring system that watches over-voltage, resistance and other key areas that you would not be aware it is failing without this help. The code is designed to help you or your mechanic troubleshoot the diesel engine faster and get to the failed parts before serious problems arise.
It is a package deal as you will not find an FMI code on a stand alone basis. You may find an SPN code without an FMI code following it but that is rare.
Thankfully, there are only 30 codes for this FMI network. That makes it easier to understand and know what the trouble is. Here is a little table containing all the FMI codes so you can have them at your fingertips when you see them on your display screen.
|0||Data Valid but Above Normal Operational Range, Most Severe Level||12||Bad Intelligent Device or Component|
|1||Data Valid but Below Normal Operational Range, Most Severe Level||13||Out of Calibration|
|2||Data Erratic, Intermittent or Incorrect (rationality)||14||Special Instructions|
|3||Voltage Above Normal, or Shorted to High Source||15||Data Valid but Above Normal Range : Least Severe Level|
|4||Voltage Below Normal, or Shorted to High Source||16||Data Valid but Above Normal Range: Moderately Severe Level|
|5||Current Below Normal, or Open Circuit||17||Data Valid but Below Normal Range: Least Severe Level|
|6||Current Above Normal, or Grounded Circuit||18||Data Valid but Below Normal Range: Moderately Severe Level|
|7||Mechanical System not Responding or Out of Adjustment||19||Received Network Data in Error: (Multiplexed Data)|
|8||Abnormal Frequency or Pulse Width or Period||20||Data Drifted High (rationality high)|
|9||Abnormal Update Rate||21||Data Drifted Low (rationality low)|
|10||Abnormal Rate of Change||22 - 30||Reserved for SAE Assignment|
|11||Failure Code not Identifiable||31||Condition Exists|
When you see an SPN code number followed by FMI 0 that means that you should be getting a red warning light on your dash. That code and color of a warning tell you that this is a severe problem that cannot have diagnostic delays.
When it says most severe level, you are out of options. You are in a dangerous situation and your engine could be derated and you won’t be able to travel very far or very fast.
This FMI code is telling you that you are in a risky situation but instead of being over the normal operating range, you are under it. That means that you should be getting a red warning light on your dashboard as this situation is as bad as getting FMI 0.
You need to take care of the problem as soon as possible before your engine derates. It is a very serious problem that cannot be ignored. Hopefully, it does not happen when you are far from home.
Most, if not all, FMI codes are electrical-related. This code is telling you that you have a voltage problem and that problem could possibly be a short somewhere in the system.
You may need a meter to help you find the short or the voltage problem but it is best to let the trained mechanic handle the work. Working on engines these days is tricky and takes specialized tools and training.
These new tools are also very expensive and can cost hundreds of dollars.
If you understand electricity and how it works, this code is informing you of a problem with the current levels. It is under the normal operating level. Or something has come loose or disconnected and you are now operating under an open circuit.
Unfortunately, it does not say what color of warning light you will get or if it even triggers a warning light. Just be cautious and make sure you get to a mechanic as quickly as you can.
The severity of this code will depend on the SPN code it follows.
J1939 Data Link - Abnormal Update Rate. Communication between the electronic control module (ECM) and another device on the SAE J1939 data link has been lost. Engine speed will ramp down and remain at idle.
The ECM does not receive a valid J1939 message from a multiplexed device for more than 1 second. The ECM detects an open or short circuit condition in the J1939 data link harness.
This information is taken from the data sheet found at this link. Unfortunately, data sheets are not always accessible for every code.
In other words, the ECM cannot detect what the trouble is so it cannot trigger the proper code. However, there are possible sources when you are experiencing trouble but getting no codes. Here are some of those possible issues:
- Loss of engine power
- No-crank condition
- Engine stalling issues
- Hard-start condition
- Increased fuel consumption
- Engine knock
A failure detected that can be identified to be the result of not being properly calibrated. This may be the case for a subsystem that can identify that the calibration attempting to be used by the controller is out of date.
Or it may be the case that the mechanical subsystem is determined to be out of calibration. This failure mode does not relate to the signal range definition as do many of the FMIs (source)
Special Instructions" is the FMI to be used when the on-board system can isolate the failure to a small number of choices but not to a single point of failure.
When this FMI is used, there is a clear necessity for the service technician to take some action to complete the specific diagnosis, and the Manufacturer has provided instructions for the completion of that diagnosis.
There are two cases where this will be used: 1. for emission-related diagnostics where the particular failure cannot be separated between a sensor out of range and the case where the actual value is at the edge of a diagnostic region, and 2. for the older SPN 611 to 615 where the problem is in determining which of two or more circuits (which may interact) is the one that needs repair. (same source as above)
The explanations at this source are quite technical but they will describe everything you need to know about the code.
As technology makes everything even more complicated, you will get more codes. These codes may not be as easy to understand as the current FMI system.
Don’t worry if you do not understand the codes. Just make sure you understand the severity and immediacy of the problem when you see those codes. Then when you see them, go to a qualified mechanic to handle the problem.