Allison 1000 & 2000 Gen 5 Fault Code:P0561 System Voltage – Performance

CIRCUIT DESCRIPTION:
The TCM requires a switched ignition voltage input. This switched ignition voltage signal originates from the ignition switch or an ignition relay to supply voltage to wire 163 in the 80-way connector at the TCM. DTC P0561 when the TCM detects large variations in system voltage and variations near the low system voltage threshold. This DTC is only enabled with GM L96 applications.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0561 is active, the following conditions occur:
1. DTC is stored in the TCM history.
2. No response.
3. The TCM forces the Variable Modulated Main off.
4. The TCM freezes shift adapts (DNA).
5. The TCM does not illuminate the CHECK TRANS light.

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.

DIAGNOSTIC AIDS:
The following procedures are not documented in any OEM procedures or in any OEM Troubleshooting or Service Information and therefore should not be used as a method to diagnose any transmission DTCs, function, or shift quality concern:

1. Back-probing any connections used for transmission features or functions may damage and/or unlock terminals from the back-probed connector creating permanent or intermittent shorts and/or open circuits. If possible, use the J-39700 Breakout Box, the appropriate harness adapters, and appropriate magnetic overlays to troubleshoot the vehicle.

2. Load-testing any transmission-related circuits with any other electrical devices such as vehicle lamps or relays, especially with the TCM connected to the harness. Use J-39700 Breakout Box and appropriate harnesses with the diagnostic tool to monitor the circuit performance in question unless otherwise specified in the various troubleshooting information.

3. Piercing a wire to check for voltages, shorts-to-grounds or other wires anywhere in the circuit but especially at the TCM. This creates a leak path for moisture and damages the wire and insulation.

4. You may have to drive the vehicle in order to experience a fault.

5. This DTC indicates a variation in ignition voltage. Common ignition circuit problems for this DTC are a fault in the feed wires to the TCM, a defective ignition switch, or a large vehicle accessory load on the ignition circuit.

6. A vehicle charging system failure may cause this DTC under certain circumstances.

7. This DTC may indicate that an internal voltage problem has occurred inside the TCM. The use of a substitute TCM would be a good way to diagnose this problem.

8. A defective vehicle battery may induce 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 circuit condition, massage the wiring harness while watching the test equipment for a change.