Allison 1000 & 2000 Gen 5 Fault Code:P0720 Output Shaft Speed Sensor Circuit

CIRCUIT DESCRIPTION:
The speed sensors are devices which convert mechanical motion to an electrical signal. This test detects an output speed sensor circuit short to battery, ground, or open.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0720 is active, the following conditions occur:
1. If the DTC sets while shift not in process, remains in current range.
2. If the DTC sets while shift is in progress, complete shift and lock in that range.
3. The TCM forces Variable Modulated Main off.
4. DTC is stored in TCM history.
5. The CHECK TRANS light illuminates.
6. The TCM inhibits TCC engagement.
7. The TCM freezes shift adapts.

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 the DTC recurring.

DIAGNOSTIC AIDS:
DTC P0720 may be caused by:
1. W140 and/or W160 shorted to another wire in chassis harness or to ground.
2. W140 and/or W160 high resistance or open circuit.
3. Broken or defective connector assemblies allowing pushed back pins to short together.
4. Unlocked connectors, missing seal plugs allowing moisture in connectors.
5. Fatigued wires at speed sensor connectors (broken strands).
6. Incorrect pin crimps or expanded terminals.
7. Defective output shaft speed sensor.
8. Defective TCM.
9. Wire pair not twisted or not sufficiently twisted.

NOTE: Confirm that the speed sensor wiring consists of twisted pairs at the rate of 12 to 16 twists per 300 mm. These twists must extend the entire length of the wiring harness to within at least 50mm of the speed sensor connector.

NOTE: OEM Transmission warranty, or the extended coverage for parts and labor, does not cover transmission or vehicle damage caused by drivelines that do not meet the OEM specifications.

NOTE: The OEM transmission warranty, or the extended coverage for parts and labor, does not cover the repair or replacement of OEM or bodybuilder-provided components or any external wire harnesses not provided by the OEM.

Before repairing or replacing these components or circuits that caused a transmission issue, always contact the vehicle OEM call center and/or the vehicle OEM or bodybuilder service representative to verify the warranty coverage and proper payment arrangements, arrange an alternate sublet or repair plan (if needed), and get troubleshooting assistance for the repair (such as vehicle schematics, DTC trees, parts assistance, etc).