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Allison 1000 & 2000 Gen 4 Fault Codes: P0218 Transmission Fluid Over Temperature Condition

Allison 1000 & 2000 Gen 4 Fault Codes: P0218 Transmission Fluid Over Temperature Condition

 

CIRCUIT DESCRIPTION:
The flow of transmission fluid starts in the transmission pan. Fluid is then drawn through the filter and internal passages into the oil pump assembly. The oil pump pressurizes the fluid into main-pressure that is regulated at the main-pressure regulator valve. From this point, fluid is directed to the F trim solenoid and to the control-main regulator and control-main relief valve into the control-main filter assembly and on to all solenoids for use as control pressure. Hot fluid leaving the torque converter is routed through the converter flow valve to cooler lines and into the cooler assembly. The transmission oil cooler is located in the radiator. The vehicle may be equipped with an auxiliary oil cooler. The cooled fluid is returned to the transmission through the return cooler line and to the transmission lube circuit. The automatic transmission fluid temperature (TFT) sensor, which is part of the PSM, is located in the oil pan.

If the Transmission Control Module (TCM) detects a high TFT for an extended period of time, then DTC P0218 sets.

CONDITIONS FOR RUNNING THE DTC:
1. DTCs P0711, P0712, P0713 are not active.
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).
3. Engine speed is greater than 200 rpm for more than 5 seconds.

CONDITIONS FOR SETTING THE DTC:
DTC P0218 sets when the TCM detects a transmission sump temperature greater than 126°C (252°F) for 10 seconds.

ACTION TAKEN WHEN THE DTC SETS:
1. The TCM does not illuminate the CHECK TRANS light.
2. The TCM freezes shift adapts (DNA).
3. The TCM records the operating conditions when the CONDITIONS FOR SETTING THE DTC: are met. The TCM stores this information as Failure Records.
4. DTC P0218 is stored in the TCM history.
5. The TCM defaults to “hot mode” shift schedule where 4th-range is held and TCC is inhibited to increase engine speed and improve cooler flow.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
1. A Scan Tool may be used to clear the code from the TCM history.
2. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring.
3. The TCM cancels the DTC default actions when the fault no longer exists, and the DTC passes test.

DIAGNOSTIC AIDS:
1. Verify the customer’s driving habits, such as trailer towing, etc.
2. The Scan Tool transmission fluid temperature (TFT) should rise steadily during warm-up cycles and then stabilize.
3. DTC P0218 may set after DTC P0711 (not active) has set. Follow the diagnostic information for DTC P0711 before proceeding to the diagnostic for DTC P0218. Repairing the condition that set DTC P0711 will likely eliminate DTC P0218.

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Allison 1000 & 2000 Gen 4 Fault Codes: P0123 Pedal Position Sensor Circuit High Voltage

Allison 1000 & 2000 Gen 4 Fault Codes: P0123 Pedal Position Sensor Circuit High Voltage

 

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) receives input on throttle position from either a Throttle Position Sensor (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 transmission 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.

CONDITIONS FOR RUNNING THE DTC:
1. 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).
2. DTC P0122 Throttle/Pedal Position Sensor/Switch A Circuit Low Input is not active.

CONDITIONS FOR SETTING THE DTC:
DTC P0123 sets when the TCM detects a throttle position sensor voltage greater than 4.75 for 5 seconds.

ACTION TAKEN WHEN DTC SETS:
1. DTC P0123 is stored in the TCM history.
2. The TCM uses the default throttle value.
3. The TCM freezes shift adapts (DNA).
4. The TCM inhibits TCC engagement.
5. The CHECK TRANS light is illuminated.

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:
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.

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Allison 1000 & 2000 Gen 4 Fault Codes: P0122 Pedal Position Sensor Circuit Low Voltage

Allison 1000 & 2000 Gen 4 Fault Codes: P0122 Pedal Position Sensor Circuit Low Voltage

 

CIRCUIT DESCRIPTION:
The Transmission Control Module (TCM) receives input on throttle position from either a Throttle Position Sensor (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 transmission 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.

CONDITIONS FOR RUNNING THE DTC:
1. 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).
2. DTC P0123 Pedal Position Sensor Circuit High Voltage is not active.

CONDITIONS FOR SETTING THE DTC:
DTC P0122 sets when the TCM detects a throttle position sensor voltage less than 0.55V for 5 seconds.

ACTION TAKEN WHEN THE DTC SETS:
1. DTC P0122 is stored in the TCM history.
2. The TCM uses the default throttle value.
3. The TCM freezes shift adapts (DNA).
4. The TCM inhibits TCC engagement.
5. The CHECK TRANS light is illuminated.

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:
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.

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Allison 1000 & 2000 Gen 4 Fault Codes: P1688 Unmanaged Engine Torque Delivered To TCM Signal

Allison 1000 & 2000 Gen 4 Fault Codes: P1688 Unmanaged Engine Torque Delivered To TCM Signal

 

CIRCUIT DESCRIPTION:
The GM 8.1 liter gasoline engine is used in some medium duty applications. The 8.1 liter engine uses a 3-wire system to communicate engine torque data/requests between the powertrain control module (PCM) and the transmission control module (TCM).

Unmanaged engine torque is sent from the PCM to the TCM over wire 109 (GM wire 2467).

CONDITIONS FOR RUNNING THE DTC:
1. The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM).
2. Engine speed is greater than 200 rpm and less than 7500 rpm for 5 seconds.
3. Pulse Width Modulation (PWM) driver demand torque option is selected in transmission calibration.

CONDITIONS FOR SETTING THE DTC:
DTC P1688 sets if unmanaged (gross) engine torque signal (circuit 2467) is under 1.5 percent or over 98.5 percent for more than a 2 second period.

ACTION TAKEN WHEN THE DTC SETS:
1. DTC P1688 is stored in the TCM history.
2. The CHECK TRANS light illuminates on the second occurrence.
3. The TCM defaults to a calculated unmanaged torque (gross) input value using throttle and engine speed.

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:
An Intermittent condition may be the cause of the problem. Return the vehicle to the OEM for further troubleshooting.

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