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Here is a comprehensive write-up of the Mercedes NAG1 5-speed automatic transmission that was used in the 2009-2011 Challengers. What is particularly interesting is a discussion of the various limp-mode functions and adaptives:

NAG1 (5-Speed) Automatic Transmission
Dodge Challenger 2009-2011

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 electro-hydraulic 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 kick-down. 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 adaptive's. Resetting adaptive's will set the adaptive's 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 procedure.

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 adaptive's 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 adaptive's under the 10 minute time frame using the scan tool Store Adaptive's procedure.


The TCM is located under the left side of the instrument panel for left hand drive vehicles
. There are two connectors that attach to the unit for control C1 and C2.
Access is obtained by removing the lower kick panel (has deck lid release button) and cover below the steering wheel and instrument cluster.

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.

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 (Starscan/StarMobile) 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 shift time 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.

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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