Honda Service Check Signal Function
This bulletin applies to 2017 Honda Odyssey and all late model Honda vehicles equipped with SCS (service check signal).
The software for the legacy HDS and the new i-HDS offers a standalone function called service check signal or SCS. You'll find it on various screens of the tool. When you turn it on, the tool shorts the SCS terminal in the 16-pin DLC directly to ground.
In the legacy HDS software, you'll find this function on the Select Mode screen, but it's also available as an icon on the Data List or Snapshot screens. When it's turned on, you'll see SCS blinking in the lower right corner of the screen. In addition, this function turns off any time you exit the screen.
In the i-HDS software, you'll find an SCS icon at the top of most screens. Once you turn the function on, it doesn't turn off when you switch to a different screen. Instead, it stays on until you turn it off by either selecting the icon or completely exiting the software.
WHAT IT DOES
Shorting the SCS terminal at the DLC tells the ECM/PCM to run diagnostic checks on a number of vehicle systems. While the SCS function is turned on, you'll see various indicators come on in the instrument panel and the MID may show F-CAN DTCs. Because of this, the SCS function offers you another way to read vehicle DTCs.
Besides diagnostic checks, the SCS function also helps during troubleshooting. You can use it to bypass the two-trip requirement on certain DTCs and to shut down the ECM/PCM before checking wiring harness circuits or replacing parts. Here's a closer look:
Bypassing the Two-Trip Requirement
After clearing certain fuel system DTCs, the ECM/PCM software may require you to drive two separate trips before the DTC will set again. This is called a two-trip requirement. After the first trip, the ECM/PCM sets a pending DTC but doesn't record a freeze frame or on-board snapshot.
To bypass the two-trip requirement and set any DTCs in a single trip, follow these steps:
1. Turn the ignition to ON, and connect the i-HDS.
2. Turn on the SCS function.
3. Once the MIL comes on, test-drive the vehicle with the i-HDS connected.
Shutting Down the ECM/PCM
The ECM/PCM can stay active for several hours after vehicle shutdown. During that time, the software records data to memory and runs certain diagnostic checks. To protect the ECM/PCM from damage, you need to shut down this activity before unplugging the unit from its wiring harness. To do this, follow these steps.
1. With the ignition turned to ON, connect the i-HDS.
2. Turn the ignition to OFF, and turn on the SCS function. To make sure the SCS is working, check the DST-I screen. It should read Communicating - Do not Disconnect.
3. To complete the process, turn off the SCS function and disconnect the i-HDS.
Once you've completed these steps, it's safe to unplug the ECM/PCM connectors.
Be sure to review all of the steps needed when using the SCS function. Missing a step could affect your troubleshooting or damage the ECM/PCM, so be sure to follow every step to the letter!
And one more thing, Honda has a Tech2Tech video in the works that will show the SCS function in action.