Using the Correct AFIT Power Adapter

When testing an engine using the Active Fuel Injector Tester (AFIT) kit on most GM vehicles, the tools must be connected to power correctly in order for proper communication. The AFIT kit includes a 12V power cord that plugs into an accessory power outlet, a battery power adapter, and a 12V power adapter that plugs into a wall outlet to power the Main Control Unit (MCU). (Fig. 3)

Fig. 3

The AFIT MCU can be used in the engine compartment or placed in the vehicle cab with the 12V power cord plugged into the vehicle’s accessory power outlet. (Fig. 4, A) For vehicles that do not power the accessory power outlet unless the key is on, the included battery power adapter cable (Fig. 4, B) can be used instead of the 12V power cord.

The DMU (Drive & Measurement Unit) can be placed in the engine compartment and the power clips connected to the vehicle’s 12-volt battery or the remote battery terminals on vehicles that do not have the battery located under the hood.

With the DMU connected to the AFIT MCU, press the On/Off button to power on the MCU. The MCU will perform a self-test to check the vehicle’s battery voltage. If there is a lower amount of voltage in the battery, the tester will flash a Low Battery message. To avoid losing power while testing, the vehicle’s battery should be properly charged.

The 12V power adapter that plugs into a wall outlet (Fig. 4, C) only should be used to supply power to the MCU when connected to a computer when it’s necessary to update the tool or upload test records.

The wall adapter will power up the MCU but does not provide sufficient power to test the fuel injection system. This applies if the wall adapter is plugged into a vehicle’s 110V power outlet, if equipped, as well.

Fig. 4

If the correct power connections are not made, an error message may be displayed that the MCU is not communicating with the DMU. (Fig. 5)

Fig. 5


Software Downloads and User Guides

Before using the AFIT, always be sure it is updated with the latest software. Software updates are available from the GM Dealer Equipment website. Download the software through the Service Workbench selection of “Essential Tools – Software Updates” in GM GlobalConnect (U.S. only). Open the file and follow the instructions.

In Canada, the software is available for download through the Service Application selection of GM Special Tools & Equipment – Software Updates in GM GlobalConnect.

The software downloads page on the website also includes links to a number of AFIT user guides.

– Thanks to Chuck Berecz

Download the Latest AFIT Software Update
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  1. The G7 is the correct adapter for the 2020 Silverado 5.3L engine. The SENT adapter CH-47976-507 is different than the regular adapters. It was added to the AFIT quite a few years ago. The SENT adaptor allows the AFIT DMU module to convert digital Single Edge Nibble Transmission (SENT) fuel pressure sensor signals into analog signals. Once installed, the adaptor stays on the DMU. If there is a problem with the SENT adapter, call 1-800-GM-TOOLS for assistance.

  2. what sent adaptor, and cables needed to hook up to a 2020 Silverado 5.3l says I have the wrong sent adaptor current sent adaptor ch-47976-507 g7 cable ?????

  3. When using the AFIT, the DMU should be placed in the engine compartment and connected to the vehicle’s 12-volt battery and to the MCU. If the correct power connections are not made, an error message may be displayed that the MCU is not communicating with the DMU. For technical assistance with the AFIT, call 1-800-GM-TOOLS (1-800-468-6657).

  4. Jeremiah Schaefer says:

    After performing a successful AFIT Injector Test on a 15 Tahoe and unloading it to my PC another tech tried to perform an Injector Test and the message “Connect DMU to vehicle battery”keeps coming up and will not allow test to proceed.

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