Perform a Brake Air Differential Self-Test on the 1200 only, not using a Trailer or a Dolly:
Set-up and perform the Brake Differential Self-Test:
This Differential Self-Test is performed to verify your 1200 Certifier is functioning properly so that
when a Differential Test is performed on an actual trailer or dolly in the future, the user will know that
the results are accurate.
The Differential Test only applies to vehicles equipped to tow other air brake vehicles, such as
dollies, short semi-trailers (for doubles and triples) and B-train front semi-trailers. The test
requirements are specified in FMVSS-121, Paragraph S5.3.5.
The purpose of a Differential Test is to verify the control signal passed through the rear SERVICE
glad-hands of a trailer being tested, to another towed trailer or dolly, varies no more than the
permitted amount from the signal controlling the brakes on the vehicle being tested. This permitted
difference depends on the SERVICE/Control input pressure to the vehicle being tested.
5 psi to less than 20 psi
1 psi difference or less
20 psi to less than 40 psi
2 psi difference or less
40 psi or greater
5% of the input pressure or less
This test requires attachment of the double glad-hand fitting assembly, also known as the
“Differential Kit” or “Diff Kit” (PN 18115). The Diff Kit is an option which can be purchased
separately from the 1200 Certifier.
1. Now that the Air Leak and 121 Timing self-tests have passed, a popup should be displayed telling
you to
connect the Diff Kit.
Before that can be done,
disconnect the 50 CI tank from the
SERVICE glad-hand.
Leave all the other connections intact.
2. The Diff Kit now needs to be attached to the SERVICE glad-hand. To do this properly,
notice
the “Air Flow” direction sticker on the Diff Kit.
Connect the SERVICE glad-hand from the 1200
Certifier to the correct glad-hand on the Diff Kit, which is identified by being sure the Air Flow will be
flowing out of the SERVICE glad-hand and into the Diff Kit. Then click on “Continue” in the popup.
Nat’l Highway Traffic Safety Admin., DOT
Lite-Check CERTIFIER 1200 Operations Manual
13
This test continues on the next page.
