Allison 1000 & 2000 Gen 5 Fault Code:P0122 Pedal Position Sensor Circuit – Low Voltage

CIRCUIT DESCRIPTION:
The TCM receives input on throttle position from either a TPS or a signal transmitted by the engine electronic controls.

Vehicles not equipped with electronically-controlled engines have a TPS attached to the engine fuel control linkage. The TPS continuously sends the exact throttle position to the TCM.

The TPS is a sliding resistor sensor (potentiometer) actuated by a mechanical linkage. The TCM delivers a constant voltage to one terminal of the TPS resistive strip. The other TPS terminal connects to ground. The resistor contacts of the TPS are connected to provide a regulated voltage signal input to the TCM.

When actuated by the mechanical throttle cable, the contacts of the resistor move along the resistive strip. As the contacts slide along the resistive strip, a voltage is sent to the TCM. At each increment of 0.178 mm (0.007 inch) along the resistive strip, the contacts deliver a different voltage to the TCM. The different voltages are interpreted as throttle sensor movement. The TCM converts travel distance (mm) into throttle opening percentage.

ACTION TAKEN WHEN THE DTC SETS:
1. DTC P0122 is stored in the TCM history.
2. The TCM uses the default throttle value, based on engine torque and speed.
3. The TCM forces Variable Modulated Main off.
4. The TCM inhibits Torque Converter Clutch (TCC) engagement.
5. The CHECK TRANS light illuminates (non-OBD II strategy).

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:
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.
3. Poor terminal tension.
4. A chafed wire.
5. 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.

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