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Discussion Starter · #1 ·
TCM - Main Operations

Lets look at how our Automatic Transmission in the Challenger and its TCM operate and how its described in Chrysler/Dodge documentation.

Here are some general highlights of our automatic transmission:

The NAG1 (5-Speed) Automatic Transmission

The NAG1 automatic transmission is an electronically controlled 5-speed transmission
with a lock-up clutch in the torque converter. The ratios for the gear stages are obtained
by 3 planetary gear sets. Fifth gear is designed as an overdrive with a high-speed ratio.

NAG1 identifies a family of transmissions and means “N”ew “A”utomatic “G”earbox, generation 1.

Various marketing names are associated with the NAG1 family of transmissions, depending
on the transmission variation being used in a specific vehicle. Some examples of the marketing
names are: W5A300, W5A380, and W5A580. The marketing name can be interpreted as follows:

1. W = A transmission using a hydraulic torque converter.
2. 5 = 5 forward gears.
3. A = Automatic Transmission.
4. 580 = Maximum input torque capacity in Newton meters.

The gears are actuated electronically/hydraulically. The gears are shifted by means of an
appropriate combination of three multi-disc holding clutches, three multi-disc driving
clutches, and two freewheeling clutches.

Electronic transmission control enables precise adaptation of pressures to the respective
operating conditions and to the engine output during the shift phase which results in a
significant improvement in shift quality.

The transmission control is divided into the electronic and hydraulic transmission control
functions. While the electronic transmission control is responsible for gear selection and
for matching the pressures to the torque to be transmitted, the transmission's power supply
control occurs via hydraulic elements in the electrohydraulic control module. The oil supply
to the hydraulic elements, such as the hydrodynamic torque converter, the shift elements
and the hydraulic transmission control, is provided by way of an oil pump connected with
the torque converter.

The Transmission Control Module (TCM) allows for the precise adaptation of pressures
to the corresponding operating conditions and to the engine output during the gearshift phase,
resulting in a noticeable improvement in shift quality. The engine speed limit can be reached
in the individual gears at full throttle and kickdown. The shift range can be changed in the
forward gears while driving, but the TCM employs a downshift safeguard to prevent
over-revving the engine. The system offers the additional advantage of flexible adaptation
to different vehicle and engine variants.

In order to ensure a safe driving state and to prevent damage to the automatic transmission,
the TCM control module switches to limp-home mode in the event of critical faults.
A diagnostic trouble code (DTC) assigned to the fault is stored in memory. All solenoid
and regulating valves are thus de-energized.

The net effect is:
1. The last engaged gear remains engaged.
2. The modulating pressure and shift pressures rise to the maximum levels.
3. The torque converter lockup clutch is deactivated.

In order to preserve the operability of the vehicle to some extent, the hydraulic control
can be used to engage 2nd gear or reverse using the following procedure:

1. Stop the vehicle.
2. Move selector lever to "P".
3. Switch off engine.
4. Wait at least 10 seconds. Start engine.
5. Move selector lever to D: 2nd gear.
6. Move selector lever to R: Reverse gear.

The limp-home function remains active until the DTC is rectified or the stored DTC is erased
with the appropriate scan tool. Sporadic faults can be reset via ignition OFF/ON.

The adaptation procedure requires the use of the appropriate scan tool. This program allows
the electronic transmission system to re-calibrate itself. This will provide the proper baseline
transmission operation. The adaptation procedure should be performed if any of the following
procedures are performed:

1. Transmission Assembly Replacement
2. Transmission Control Module Replacement
3. Clutch Plate and/or Seal Replacement
4. Electro-hydraulic Unit Replacement or Recondition

1. With the scan tool, reset the Transmission adaptives.
Resetting the adaptives will set the adaptives to factory settings.

For Upshift adaptation, the Transmission temperature must be greater than 60°C (140°F)
and less than 100°C (212°F). Failure to stay within these temperature ranges will void this

2. Drive the vehicle until the transmission temperature is in the specified range.

3. Perform 4 to 5 coast downs from 5th to 4th gear and then 4th to 3rd gear.

4. From a stop, moderately accelerate the vehicle and obtain all forward gear ranges while keeping
the Engine RPM below 1800 RPM. Repeat this procedure 4 to 5 times.

5. Obtaining 5th gear may be difficult at 1800 RPM. Allow transmission to shift into 5th gear at a higher RPM then lower the RPM to 1800 and perform manual shifts between 4th and 5th gears using the shift lever.

6. The TCM will store the adaptives every 10 minutes. After completion of the adaptation procedure make sure the vehicle stays running for at least 10 minutes.

7. It is possible to manually store the adaptives under the 10 minute time frame using the scan tool Store Adaptives procedure.

The TCM is located under the left side of the instrument panel for left hand drive vehicles.

The electronic control system consists of various components providing inputs to the
transmission control module (TCM). The TCM monitors transmission sensors, shift lever
position, and bus messages to determine transmission shift strategy. After shift strategies
are determined, the TCM controls the actuation of transmission solenoids, which controls
the routing of hydraulic fluid within the transmission, by moving a sequence of four valves
to make a shift occur.

(Continued on next message)

· Registered
103 Posts
Discussion Starter · #2 ·
TCM Main Operations
Part II

The NAG1 electronic transmission has a fully adaptive control system. The system performs
its functions based on continuous real-time sensor feedback information. In addition the TCM
receives information from the PCM (engine management) and ABS (chassis systems) controllers
over the CAN bus.

The CAN bus is a high-speed communication bus that allows real time control capability between
various controllers. Most messages are sent every 20 milliseconds. This means critical information
can be shared between the transmission, engine, and ABS controllers. The CAN bus is a two wire
bus with a CAN Bus (+) circuit and a CAN Bus (-) circuit. These circuits are twisted pairs in the
harness to reduce the potential of radio and noise interference.

The transmission control system automatically adapts to changes in engine performance, vehicle
speed, and transmission temperature variations to provide consistent shift quality. The control
system ensures that clutch operation during up-shifting and downshifting is more responsive
without increased harshness. The TCM activates the solenoid valves and moves valves in the
valve body to achieve the necessary gear changes. The required pressure level is calculated
from the load condition, engine speed. Vehicle speed (from ABS module) and transmission
oil temperature, matched to the torque to be transmitted. The TCM is located under the left
side of the instrument panel for left hand drive vehicles.

The "Shift Lever Assembly" (SLA) has sensors that are monitored by the TCM to calculate
shift lever position. The reverse light switch, an integral part of the SLA, controls the
reverse light relay control circuit. The Brake/Transmission Shift Interlock (BTSI) solenoid
and the park lockout solenoid (also part of the SLA) are controlled by the TCM.
The PCM and ABS broadcast messages over the controller area network (CAN) bus
for use by the TCM. The TCM uses this information, with other inputs, to determine the
transmission operating conditions.

The TCM:
1. determines the momentary operating conditions of the vehicle.
2. controls all shift processes.
3. considers shift comfort and the driving situation.

The TCM controls the solenoid valves for modulating shift pressures and gear changes. Relative
to the torque being transmitted, the required pressures are calculated from load conditions, engine
rpm, vehicle speed, and ATF temperature.
The following functions are contained in the TCM:

1. Shift Program
2. Downshift Safety
3. Torque Converter Lock-Up Clutch.
4. Adaptation.

The TCM continuously checks for electrical problems, mechanical problems, and some
hydraulic problems.

When a problem is sensed, the TCM stores a diagnostic trouble code (DTC). Some of these
codes cause the transmission to go into "Limp-In" or "default" mode. Some DTCs cause
permanent Limp-In and others cause temporary Limp-In. The NAG1 defaults in the current
gear position if a DTC is detected, then after a key cycle the transmission will go into Limp-in,
which is mechanical 2nd gear. Some DTCs may allow the transmission to resume normal
operation (recover) if the detected problem goes away. A permanent Limp-In DTC will
recover when the key is cycled, but if the same DTC is detected for three key cycles the
system will not recover and the DTC must be cleared from the TCM with the appropriate
scan tool.

Selector Lever Position:
A series of sensors in the SLA inform the TCM of the position of the selector lever.
The TCM monitors the SLA for all shift lever positions through five position circuits.
The SLA provides a low-current 12-volt signal to the TCM. The TCM compares the
on/off signals to programmed combinations to determine the exact position of the shift lever.

ATF Temperature Sensor:
The ATF temperature sensor is a positive temperature co-efficient (PTC) thermistor.
It measures the temperature of the transmission fluid and is a direct input signal for the
TCM. The temperature of the ATF has an influence on the shifttime and resulting shift
quality. As the temperature rises, resistance rises, and therefore, the probing voltage is
decreasing. Because of its registration, the shifting process can be optimized in all
temperature ranges.

The ATF temperature sensor is wired in series with the park/neutral contact. The
temperature signal is transmitted to the TCM only when the reed contact of the
park/neutral contact is closed because the TCM only reads ATF temperature
while in any forward gear, or REVERSE. When the transmission is in PARK or
NEUTRAL, the TCM will substitute the engine temperature for the ATF temperature.
Starter Interlock

The TCM monitors a contact switch wired in series with the transmission temperature
sensor to determine PARK and NEUTRAL positions. The contact switch is open in
PARK and NEUTRAL. The TCM senses transmission temperature as high (switch
supply voltage), confirming switch status as open. The TCM then broadcasts a message
over CAN bus to confirm switch status. The PCM receives this information and allows
operation of the starter circuit.

N2 and N3 Speed Sensors:
The N2 and N3 Input Speed Sensors are two Hall-effect speed sensors that are mounted
internally in the transmission and are used by the TCM to calculate the transmission's input
speed. Since the input speed cannot be measured directly, two of the drive elements are
measured. Two input speed sensors were required because both drive elements are not
active in all gears.

(Continued on next message)

· Registered
103 Posts
Discussion Starter · #3 ·
CAN Bus Indirect Input Signals:
A 2.5-volt bias (operating voltage) is present on the CAN bus any time the ignition switch
is in the RUN position. Both the TCM and the ABS apply this bias. On this vehicle, the
CAN bus is used for module data exchange only.
The indirect inputs used on the NAG1 electronic control system are:

1. Wheel Speed Sensors.
2. Transfer Case Switch Status.
3. Brake Switch.
4. Engine RPM.
5. Engine Temperature.
6. Cruise Control Status.
7. Gear Limit Request.
8. Throttle Position - 0% at idle, 100% at WOT. If open, TCM assumes idle (0% throttle opening).
9. Odometer Mileage
10. Maximum Effective Torque.
11. Engine in Limp-In Mode/Mileage Where DTC Was Set.

The BTSI solenoid prevents shifting out of the PARK position until the ignition key is in
the RUN position and the brake pedal is pressed. The TCM controls the ground while
the ignition switch supplies power to the BTSI solenoid. The PCM monitors the brake
switch and broadcasts brake switch status messages over the CAN C bus. If the park
brake is depressed and there is power (Run/Start) to SLA, the BTSI solenoid deactivates.

The basic shift schedule includes up and downshifts for all five gears. The TCM adapts
the shift program according to driving style, accelerator pedal position and deviation of
vehicle speed. Influencing factors are:

1. Road Conditions.
2. Incline, Decline and Altitude.
3. Trailer Operation, Loading.
4. Engine Coolant Temperature.
5. Cruise Control Operation.
6. Sporty Driving Style.
7. Low and High ATF Temperature.

Selector lever downshifts are not performed if inadmissible high engine rpm is sensed.

To equalize tolerances and wear, an automatic adaptation takes place for:
1. Shift Time.
2. Clutch Filling Time.
3. Clutch Filling Pressure.
4. Torque Converter Lock-Up Control.
Adaptation data may be stored permanently and to some extent, can be diagnosed.

Driving Style Adaptation:
The shift point is modified in steps based on the information from the inputs.
The control module looks at inputs such as:

1. vehicle acceleration and deceleration (calculated by the TCM).

2. rate of change as well as the position of the throttle pedal (fuel injection information from the PCM).

3. lateral acceleration (calculated by the TCM).

4. gear change frequency (how often the shift occurs).

Based on how aggressive the driver is, the TCM moves up the shift so that the present
gear is held a little longer before the next upshift. If the driving style is still aggressive, the
shift point is modified up to ten steps. If the driving returns to normal, then the shift point
modification also returns to the base position.

This adaptation has no memory. The adaptation to driving style is nothing more than a
shift point modification meant to assist an aggressive driver. The shift points are adjusted
for the moment and return to base position as soon as the inputs are controlled in a more
normal manner.


Permanent Limp-In Mode:
When the TCM determines there is a non-recoverable condition present that does not
allow proper transmission operation, it places the transmission in permanent Limp-In Mode.
When the condition occurs the TCM turns off all solenoids as well as the solenoid supply
output circuit. If this occurs while the vehicle is moving, the transmission remains in the
current gear position until the ignition is turned off or the shifter is placed in the "P" position.
When the shifter has been placed in "P," the transmission only allows 2nd gear operation.
If this occurs while the vehicle is not moving, the transmission only allows operation in
2nd gear.

Temporary Limp-In Mode:
This mode is the same as the permanent Limp-In Mode except if the condition is no longer
present, the system resumes normal operation.

Under Voltage Limp-In Mode:
When the TCM detects that system voltage has dropped below 8.5 volts, it disables
voltage-dependant diagnostics and places the transmission in the temporary Limp-In
Mode. When the TCM senses that the voltage has risen above 9.0 volts, normal
transmission operation is resumed.

Hardware Error Mode:
When the TCM detects a major internal error, the transmission is placed in the permanent
Limp-In Mode and ceases all communication over the CAN bus. When the TCM has
entered this mode normal transmission operation does not resume until all DTCs are
cleared from the TCM.

Loss of Drive:
If the TCM detects a situation that has resulted or may result in a catastrophic engine or
transmission problem, the transmission is placed in the neutral position. Improper Ratio,
Input Sensor Overspeed or Engine Overspeed DTCs cause the loss of drive.

Controlled Limp-in Mode:
When a failure does not require the TCM to shut down the solenoid supply, but the failure
is severe enough that the TCM places the transmission into a predefined gear, there are
several shift performance concerns. For instance, if the transmission is slipping, the controller
tries to place the transmission into 3rd gear and maintain 3rd gear for all forward drive conditions.
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