Allison 1000 & 2000 Gen 5 Fault Code:P1892 Throttle Position Sensor (TPS) PWM Signal – High Input

CIRCUIT DESCRIPTION:
The TCM can be calibrated to receive throttle information from a Pulse Width Modulated (PWM) signal. DTC P1891 sets when the TCM detects PWM throttle signal greater than calibrated percent for a calibrated time.

ACTION TAKEN WHEN THE DTC SETS:
When the DTC P1892 is active, the following conditions occur:
1. The CHECK TRANS light is not illuminated (non-OBD II strategy).
2. The DTC is stored in the TCM history.
3. The TCM freezes shift adapts (DNA).
4. TCM uses default throttle values.
5. The TCM forces Variable Modulated main off.
6. TCM inhibits the Torque Converter Clutch (TCC).

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

DIAGNOSTIC AIDS:
The TCM detects the throttle source automatically during the initial series of engine starts. The TCM may have auto-detected the wrong throttle source type. Use the diagnostic tool to reset auto-detect or select the appropriate throttle source if PWM-type sensor is not being used.

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.

You may have to drive the vehicle in order to experience a fault. Use the data obtained from failure records to determine transmission range and/or certain vehicle operating variables such as temperature, run time etc. This data can be useful in reproducing the failure mode where the DTC was set.