Allison 1000 & 2000 Gen 4 Fault Codes: P0563 System Voltage High

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) requires a switched ignition voltage input to operate. This switched ignition voltage signal originates from the ignition switch or an ignition relay to supply voltage to pins 102 and 104 in the J1 connector at the TCM.

CONDITIONS FOR RUNNING THE DTC:
1. The engine speed is greater than 450 rpm for one second.
2. The 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).

CONDITIONS FOR SETTING THE DTC:
DTC P0563 sets when the TCM detects the following condition:
12 volt TCM – Ignition voltage is above 18V for 6 out of 10 seconds.
24 volt TCM – Ignition voltage is above 32V for 6 out of 10 seconds.

ACTION TAKEN WHEN THE DTC SETS:
1. If the DTC is active while the vehicle is in a forward range, the transmission shifts to neutral, 1st, 3rd, or 5th range.
2. If the DTC is active while in reverse or neutral, the transmission shifts to neutral.
3. If the shift selector is moved to a forward range, the transmission shifts to neutral, 1st, 3rd, or 5th range. If the shift selector is moved to reverse or neutral, the transmission shifts to neutral. Diagnostic response honors the inhibit latched at the time the DTC is set. If a latched inhibit is present and PRNDL is incorrect, the transmission shifts to neutral range. If PRNDL is correct, the GPI request is responded to.
4. The CHECK TRANS light is illuminated.
5. The TCM inhibits TCC engagement.
6. The TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may 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:
A defective vehicle charging system that is overcharging may cause this DTC.

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.