http://www.msdignition.com/uploadedF...structions.pdf
The PN 7530T Ignition incorporates a unique Traction Control Detection (TCD) circuit. This software code monitors the magnetic pickup circuit for changes that would only come from an installed traction control device that would modify the signal from the mag pickup. If a modification is sensed in this circuit an Alert will be set and the status LED will flash a Code 4. This Alert will continue to flash until the ignition is kept turned On for 24 hours in order to reset. A 4000 rpm TCD Rev Limit is activated until the 24 hour TCD timer is elapsed or reset by an NHRA official.