Allison 1000 & 2000 Gen 4 P0719 Brake Switch ABS Input Low

CIRCUIT DESCRIPTION:
If the vehicle is equipped with anti-lock brake system (ABS), an interface between the ABS and TCM is required. This interface allows disengagement of the Torque Converter Clutch (TCC) when the ABS is activated.

This ABS action is initiated with a discrete input from the ABS system, when the ABS is activated a ground signal is sent to TCM input wire 113. This may be a ground signal direct from the ABS controller or a positive signal from the ABS controller that powers a relay field coil to supply a ground through the relay contacts. (Some ABS systems require that the ground signal be switched through a relay.)

CONDITIONS FOR RUNNING THE DTC:
1. Components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 18V and less than 32V (24V TCM).
2. DTCs P0721, P0722 are not active.

CONDITIONS FOR SETTING THE DTC:
DTC P0719 will set after the TCM detects one or more vehicle acceleration cycles where the TCM ABS brake switch input is in the “ON” activated state.

ACTION TAKEN WHEN THE DTC SETS:
1. The TCM uses the default assumption that the ABS is OFF.
2. DTC P0719 is stored in the TCM history.
3. The CHECK TRANS light illuminates.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool can be used to clear the code from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring.

DIAGNOSTIC AIDS:
Inspect the wiring for poor electrical connections at the TCM. Look for the following conditions:
1. A bent terminal.
2. A backed-out terminal.
3. A damaged terminal.
4. Poor terminal tension.
5. A chafed wire.
6. A broken wire inside the insulation.

When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.

ABS system interface to the TCM input can be wired one of three different ways, check with the OEM for proper wiring information concerning ABS applied input before troubleshooting.