Adding Additional Inputs And Outputs Is Easy With Holley EFI's CAN Input/Output Module


Adding Additional Inputs And Outputs Is Easy With Holley EFI's CAN Input/Output Module


For high performance machines in the 21st Century, it’s all about control. Horsepower has never been easier to make, but to apply that new-found power means exerting intelligent control over how that power is applied. Electronics have become the easiest way to capture the data, create, and maintain that control.

Holley has built quite a name with its line of high-performance fuel injection systems and has expanded the product lines to include affordable ECU packages like the HP and Terminator X and Terminator X MAX line of ECUs. While these systems use the same basic software as the top-of-the-line Dominator, these more affordable ECU’s make entry into electronic fuel injection easier and more affordable.

The main advantage that the Dominator ECU enjoys over the less pricey HP and affordable Terminator X series is the aforementioned control. Where the Dominator differs is that it offers nearly 50 inputs and 36 output circuits – termed I/O’s. The less expensive HP and Terminator X are limited to a maximum of four inputs and four outputs. But drag racers, track day enthusiasts, and enlightened street drivers are beginning to realize that having more I/O’s offers opportunities. This is where the Holley EFI CAN I/O add-on module comes in, allowing users to add eight additional inputs and outputs to their current system.

Before we get into the details of how the Holley EFI CAN I/O add-on module can provide more I/O capability, let’s delve a little deeper into a few related items of interest. Any basic EFI ECU controls systems beyond just spark and fuel. The Holley HP and Terminator X’s four inputs and outputs can be custom configured to the user’s needs. For outputs, one example might be to control of a pair of electric fans, where all you have to do is tell the ECU at what temperature the fans should turn on and off. Other external controls can be aimed at something fun, like control over nitrous solenoids.

But once you become familiar with these systems, motorsports enthusiasts have discovered there are several other outputs that might be worthwhile additions to the race car. We’ve listed a few of these in the accompanying I/O chart, so we won’t go over them here. There are enough of these outputs that a simple Holley HP or Terminator X ECU does not have to capacity to control. That’s where Holley’s I/O Module comes into play.

Of course, outputs are only half the story. The other half encompasses the inputs. We can define inputs mainly as sensor information that can be added to the ECU to offer the racer or street enthusiast more information that can be used to fine tune the car for better performance. Again, we’ve come up with a list of inputs that can be used in reference as data log reference information.

IO Module Sensor Schematic

This Holley module is essentially a CAN bus device that accommodates a total of eight inputs and eight outputs that can be added to the HP or Dominator ECUs (Version V6, Build 200 or later) or Terminator X ECU (Version 2.0, Build 52 or later) to expand their capability. CAN stands for “Controller Area Network”, which is a circuitry used in computers to allow communication between devices either within the computer or with sensors outside the ECU.

Holley Input/Output digital dash switches

Another interesting option that the I/O Module offers is that you can use the Holley digital dashes to accomplish digital switching. Let’s say you’d prefer a virtual switch on the Holley LCD screen. This means after configurating a new input or output, all you have to do is touch the screen to manually turn the fan on. This virtual or digital switch will then be connected to your I/O module that controls the fan. One thing to note: a virtual switch MUST be connected to a newly programmed input or output. You cannot use a base I/O setting (meaning an already-programmed I/O, like cooling fans) to be a touch switch.

As an example of a simple I/O operation, we recently added a TH400 trans to a Chevelle running a 404ci LS engine. The TH400 trans requires a positive (+) 12-volt signal be passed to a small straight-blade connector on the transmission whenever the throttle moves to wide-open throttle. This signal increases the line pressure in the transmission, as opposed to doing so with a linkage arrangement like the Powerglide or TH350 transmissions.

We selected one of the outputs as a ground-triggered system that would present this signal through a relay when the TPS exceeds 70 percent throttle opening. This eliminates mechanical connections to the throttle and also reduces driver distractions. It’s a small thing, but makes the driver’s job at the track that much easier.

Holley’s I/O box may appear to be not much more than another electronic accessory, but in the hands of a knowledgeable tuner, this I/O module is a powerful option on the way to making your car more consistent and quicker whether on the drag strip or the street.

Examples Of Input and Output Options

GM Flex Fuel sensorShift light
Shock inputsAir shifter output
Front wheel speedLine lock solenoid
Data log trigger12v signal for TH400 transmission
Transmission pressureTorque converter dump valve
Transmission temperatureBrake lights
Pan vacuumCooling fans
Driveshaft speedWarning outputs
Dome pressureA/C Shutdown
Fuel levelSecond Fuel Pump

These are just samples of the kinds of inputs and outputs that you are able to add to your system. You can add inputs and outputs, so long as you configure them properly.

Input Types

Input TypeTrigger
H - Switched HighWhen voltage is applied. Minimum 4.5v, never exceed 24v.
G- Switched LowWhen ground is applied via a button, switch, or external device.
5 - 0-5 Volt AnalogAny 0-5v sensor input, such as TPS, MAP, Transducer, etc.
2 - 0-20 Volt Analog0-20v sensor input, any sensor.
T - ThermistorMost 2-wire coolant and air temperature sensors.
F - Frequency or Digital Speed InputDesigned for digital voltage input from a speed/rotation sensor, like a Hall effect sensor. Voltage output range can be between 4.5v to 24v.

Output Types

Output TypesOutput Form
G - Ground or Low Side outputWill output a ground trigger when activated. If switched device is over 2 amps, wire this output to the ground terminal on the switching side of the relay you are using. 
Ground pulse width modulated output (P-)Outputs a (-) low side pulse width modulated output to control solid state relays, progressive nitrous solenoids, or any other pulse width modulated devices.

NOTE: For a ground output trigger, a relay will be needed. Holley and MSD offer a selection of relay options, from a standard relay, to MSD's single, 2-channel and 4-channel Relay Modules, and all the way up to MSD's Solid-State Relays.

Creating new Inputs and Outputs

To create new inputs that your I/O Module will address, open your I/O ICF and select the "Inputs" tab. Check the ENABLE box for an input and name the input file, then select the type of input you are planning to use in the TYPE box. Once you've selected which one you are planning on using, select "Configure". You will then be moved to the CAN SETTINGS page. Make sure that CAN I/O MODULE is selected in the CAN DEVICE block. For CAN CHANNEL, select which one of the eight input slots that you will use for the input you are adding.

CAN BUS depends on your ECU type:

  • For HP EFI and Terminator X, select CAN BUS 1.
  • For Dominator ECU, select the proper channel. CAN BUS 1 is on the main harness/J1 connector, CAN BUS 2 is wired to the J3 connector.

The last two blocks in CAN SETTINGS are straightforward. CAN Serial is the serial number of the CAN I/O Module. BROADCAST RATE is how often the module sends data for that channel from the module to the ECU, in a range from .25 to 100 Hertz (Hz). 1 Hz = 1 sample per second, 100 Hz = 100 samples per second. Easy enough? The Broadcast Rate value needs to be set to the "needed" value. This means that you want to only ask for a rate that you will actually need. Putting everything to 100 Hz is going to tax the CAN bus. If you're just wanting to track fluid temperature, 1-5 Hz is just fine. If you are wanting to monitor fuel pressure to look for a potential drop, 50-100 Hz is about where you want to be. The same goes for outputs...use only the rate that is necessary.

Pin Mapping

HEFI V6 Pin Mapping toolbar location

To access the Inputs/Outputs page, click on System ICF (the Holley EFI icon in the toolbar), then click on Inputs/Outputs in the System Parameters section on the left of your screen. From here, you will see the inputs and outputs your system is currently managing.

  • FUNCTION: This is a brief description of a particular listed function
  • ASSIGNED ECU PIN: Shows which connector and which pin that function is mapped to. If the pin isn't mapped, it will display as "NOT DEFINED". Before that function will operate, it will need to be assigned to the ECU pin that the device or relay is connected to.
  • INPUT TYPE: Here, the user can determine what kind of input or output they plan on using.

Once the global folder is defined and the inputs/outputs are configured into the additional input/output charts, it's time to use the actual pin map (in the toolbox, look for the gray square the says "PIN MAP"). You will be presented with four options:

  • View Inputs - This will configure all of the input pins
  • View LCD - Used to configure up to 10 switched inputs to be activated on a touch screen digital display
  • View Outputs - Used to configure all output pins
  • View Injectors - Used to view what injectors are assigned. All of these are hard-coded. If you are using them for water/meth outputs, look at this screen to see what pins to wire your water/meth solenoids to.

All of the inputs and outputs that you created in your previous steps should be shown in the "Unassigned Inputs" or "Unassigned Outputs" area. Each will have a symbol (letter or number) next to them to indicate the kind of input or output they are (see the above table). Next, drag and drop each input or output to an ECU pin that has the same symbol. You will then need to ensure that the wiring is correct...that means make sure that the wire for the pin you've assigned your input or output to is going to where you want it to go. Taking your time and double-checking your work here will save you a lot of trouble later on down the road.


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