Allison 1000 & 2000 Gen 4 Fault Codes: P0561 Unrealistic Variations in Vehicle System Voltage

Allison 1000 & 2000 Gen 4 Fault Codes: P0561 Unrealistic Variations in Vehicle System Voltage

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) requires a switched ignition voltage input and a direct battery voltage input. 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. Battery direct voltage is supplied to pin 103 at the J1 connector.

CONDITIONS FOR RUNNING THE DTC:
1. The test becomes enabled when the engine has been running above 400 rpm for at least 0.5 seconds.
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:
P0561 sets when the TCM detects a large variation in ignition voltage or battery direct voltage. When an ignition or battery direct voltage variation of 4.0V or greater is detected for 0.5 seconds, a fault pending is reported. After 1.0 second of 4.0V or greater variation, a DTC is set with a failure response.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0561 is active, the following conditions will occur:
1. DTC P0561 is stored in the TCM history.
2. Hydraulic default is commanded. Shift selector position and hydraulic state of logic valves determine the range attained.
3. The CHECK TRANS light illuminates.
4. The TCM inhibits TCC engagement.
5. 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. You may have to drive the vehicle in order to experience a fault.
2. This DTC indicates a variation in ignition voltage or battery direct 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. Battery direct voltage problems may be due to loose or corroded battery cables, a bad connection at the battery direct feed terminal (103), or an internal TCM failure due to a burnt trace.
3. A vehicle charging system failure may cause this DTC under certain circumstances.
4. This code 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.
5. 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, massage the wiring harness while watching the test equipment for a change.