Allison 1000 & 2000 Gen 4 Fault Codes: P0562 System Voltage Low

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 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. The engine speed is greater than 450 rpm for 10 seconds.

CONDITIONS FOR SETTING THE DTC:
DTC P0562 sets when the TCM detects the following condition:
12 volt TCM – Ignition voltage is detected below 8V at 0°C (32°F) for a total of 5 out of 7 seconds. The voltage threshold is temperature dependent varying from 5V at -60°C (-75°F) to 9V at 20°C (68°F).

24 volt TCM – Ignition voltage is detected below 17V at 0°C (32°F) for a total of 5 out of 7 seconds. The voltage threshold is temperature dependent varying from 14V at -60°C (-75°F) to 18V at 20°C (68°F).

ACTION TAKEN WHEN THE DTC SETS:
1. If the DTC is active while vehicle is in a forward range, transmission shifts to neutral, 1st, 3rd, or 5th range.
2. If the DTC is active while in reverse or neutral, transmission shifts to neutral.
3. If the shift selector is moved to forward range, transmission shifts to neutral, 1st, 3rd, or 5th range.
4. If the shift selector is moved to reverse or neutral, 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, transmission shifts to neutral range. If PRNDL is correct, GPI request is responded to.
5. The CHECK TRANS light is illuminated.
6. The TCM inhibits TCC engagement.
7. 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:
1. A defective vehicle battery may allow this DTC to set. Test the vehicle battery to verify proper voltage and load capacity.
2. A defective vehicle charging system may cause this DTC.
3. Vehicle components such as an ignition switch or TCM ignition relay may cause this DTC to set and not be active, this indicates that an intermittent condition may exist in these components.

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.