Allison 1000 & 2000 Gen 5 Fault Code:P0731 Incorrect 1st Gear Ratio

CIRCUIT DESCRIPTION:
The TCM uses input from the turbine speed and the output speed sensors to determine gear ratios. The TCM then compares the known gear ratio to the calculated gear ratio for the current range. DTC P0731 sets when the calculated 1st range ratio (steady state) differs from the known 1st range ratio.

ACTION TAKEN WHEN THE DTC SETS:
When DTC P0731 is active, the following conditions occur:
1. The transmission fails to 2nd range.
2. If shift selector is moved to N (Neutral), transmission shifts to neutral; if the shift selector is moved to R (Reverse), transmission shifts to reverse unless the transmission is compromised by overspeeding or direction change, then it locks in N (Neutral).
3. DTC P0731 is stored in the TCM history.
4. The CHECK TRANS light illuminates (non-OBD II strategy).
5. The TCM forces Variable Modulated Main off.
6. TCM freezes shift adapts (DNA).
7. TCM inhibits TCC engagement.

CONDITIONS FOR CLEARING THE DTC:
The diagnostic tool may be used 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:
Inspect the speed sensor wiring and connectors for poor electrical connections. 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 or the diagnostic tool for a change.

Output or turbine tone wheel damage may cause erratic speed sensor input allowing this DTC to set.

Incorrect ratio DTCs typically indicate mechanical problems with specific clutches, i.e. C1 or C5 for 1st range.

An incorrect ratio DTC could indicate a hydraulically failed solenoid. Check the DTC information for the specific solenoid.

You may have to drive the vehicle to experience the fault.

Incorrect ratio DTCs typically indicate mechanical problems with specific clutches for range indicated.

Clutch test mode can be used to detect turbine pull-down. If turbine speed is detected, clutch damage may be indicated.

Incorrect TCM calibrations cause this DTC to set. Verify the proper TCM calibration is being used with the correct transmission family. There are different gear ratios for the 1000 and 2000 OEM transmissions.

NOTE: Transmissions equipped with Neutral at Stop could create this code if there is a stuck Neutral at Stop Pressure Control Valve (PCV) or a stuck PCS3 (Neutral at Stop only).