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Dodge diesel transmission dilemmas

Changes to Dodge’s diesel lineup have created headaches for today’s transmission specialists. Here’s some much-needed medicine to provide a cure.
Tuesday, January 15, 2013 - 10:28
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There can be a certain degree of confusion when it comes to knowing the type of transmission used in Dodge vehicles equipped with either a 5.9L or 6.7L Cummins diesel engine. Being clear concerning the engine to transmission combination goes a long way in knowing the inherent problems of each.

From 1998 to mid-2003, trucks using the 24-valve 5.9L diesels with both a powertrain control module (PCM) and engine control module (ECM) have a four-speed rear wheel drive transmission called the 47RE. In 2003, this package received some significant changes causing the transmission designation to be changed to 48RE to reflect its change. This arrangement remained in place to 2007. This is around the time the 6.7L engines hit the streets. When this rolled off the line, if it was a full chassis truck, it’s equipped with a six-speed RWD transmission called the 68RFE. If it had an incomplete chassis, an Aisin Seiki six-speed RWD transmission was used called that AS68RC.

Clutch Issues
The 1998 to 2003 5.9L/47RE application is infamously known to develop a shuttle problem with overdrive and/or the converter clutch. There are a significant number of possibilities that can cause this complaint. The most common reason is a noisy throttle position sensor (TPS) signal from the ECM to the PCM, which a re-flash per factory TSB 18-02-99 usually remedies. Many times a simple noise filter between the modules would cure it.

Of course, these methods are only compensating for the problem without actually fixing the cause. Sometimes all that is needed is to clean the battery terminals. In some instances we have seen the negative cable bolted to a painted engine block. A little sanding and cleaning along with ensuring the use of a good battery to ground cable can resolve the problem.

With the ECM mounted on the lower left side of the engine, all of the rattling from the engine can cause issues with the connection between the harness connector and module pins. Hoisting it up on the rack gives you easy access to the connector. A simple disconnect, clean and reconnect of this connector might be all that is needed. A malfunctioning alternator has been another cause for noise.

Other contributing factors to the cycling problem can be erratic VSS, brake switch or engine coolant temperature signals, a faulty P/N switch or the later style Range sensor, restricted fuel filter or the need to relearn the APPS. Some of these possibilities apply to the early 12-valve diesels as well as gas, but then they too have their very own reasons. It’s quite an inventory when you list them for all three categories. At last count, we were up to 27 total possibilities.

When the PCM was eliminated in 2003 and the ECM took control of the diesel engine and transmission, the shuttle complaint reduced considerably. In addition to this significant change, the transmission was enhanced as the new 48RE designation reflects. Part of this change included a new strategy not seen in any Dodge/Jeep vehicles equipped the RE series transmissions. The RE series previously consisted of the 42, 44 and 46REs for various size gas engines, and the 47RE for diesels. The internal solenoid used to apply the converter clutch is supplied with second gear oil enabling the solenoid to have the ability to provide converter clutch as early as second gear (Figure 4).

In other words, this Normally Open solenoid could in no way apply the converter clutch in first or reverse gears even if the solenoid was stuck closed, as it had no oil to stroke the valve. If it were mechanically stuck closed or electrically stuck closed (i.e., ground wire shorted to ground), converter clutch apply would occur immediately on top of the 1-2 shift. All gas vehicles to this day still are configured this way, but it is not so with the 48RE transmission. The lock up solenoid in this transmission is supplied with drive oil so that as soon as the selector lever is placed into drive, it has oil. This gives the solenoid the ability to apply the converter clutch as early as first gear.

Although one solenoid can apply the converter clutch as early as first gear and another second, it doesn’t mean that the computer commands it this early. In fact, the solenoid supplied with second gear oil is not commanded on until overdrive is obtained or after third gear if overdrive had been originally cancelled. The same is true with the 48RE even though it has the capability of applying the clutch as early as first gear in the Drive range. It is when manual low or manual two is selected that under certain drive conditions will it then command the converter clutch to be applied in this low range for better pulling ability. This means that should the solenoid mechanically fail closed, it will apply the converter clutch as soon as Drive is selected and stall the engine.

But the type of failure we commonly hear of on ATSG’s technical hotline is, as the vehicle is coming to a stop after a highway cruise, the solenoid is not fully exhausting after being turned off. The converter clutch does not entirely release so when the vehicle reaches a complete stop, the computer recognizes an unusual load and tries to compensate for it by increasing engine rpms. The driver is now literally standing on the brakes with everything he’s got concerned about hitting the vehicle stopped in front of him. It’s an invigorating and exhilarating moment to say the least.

To remedy this heart pounding experience requires the replacement of the solenoid. This means replacing the complete internal harness which includes the overdrive solenoid.

A notable change that took place in 2005 with this 48RE transmission is the elimination of a throttle cable linked to the transmission. This cable provided a mechanical means by which to provide a throttle opening signal to the transmission. This signal is now provided through an electric motor called a Transmission Throttle Valve Actuator (TTVA). 

If the computer lost memory due to a battery disconnect or some other reason, or the TTVA was replaced, a simple relearn procedure must be performed for proper shift points to be obtained.  The ECM will re-calibrate the motor’s current zero position when the ignition is turned on and the engine is not running for 30 seconds. During this 30 second Key On Engine Off (KOEO) period of time, you should hear the ECM rotating the motor so that it can detect its full rotation with which to determine the zero or closed throttle position. Not performing this simple little relearn can cause a variety of shift scheduling complaints.

New Problems
When the 6.7L replaced the 5.9L diesel in 2007, one of two six-speeds replaced the four-speed 48RE transmission — the full chassis vehicle 68RFE or the incomplete chassis AS68RC. Each of these transmissions has its issues that are too lengthy to list in this article.

One of the more frequent problems we see with the 68RFE is similar to its earlier 45 and 545RFE version, which is premature failure of the overdrive clutch. This can be caused by a defective line pressure transducer or a bore wearing out in the valve body with the solenoid switch valve line up. Interestingly enough, somewhere between 2009 and 2010, this transmission received a redesigned solenoid assembly and valve body. Part of this change consisted of anodizing the aluminum valve body housing to prevent wear in this area and it also included eliminating the overdrive solenoid.

The previous design solenoid assembly was capable of controlling the Overdrive Clutch from the Multi Select solenoid or the Overdrive solenoid, dependant on Manual Valve position. The elimination of the Overdrive solenoid changed the hydraulic control of the Manual Valve and the PCM strategy for shift/solenoid control, and now eliminates Manual 2/1 position, as the shifter now has a manual mode with Electronic Range Select. This change has also eliminated a Manual 2 Limp mode. Limp mode is now fourth gear only. 

As helpful as this change has been, it has introduced a new problem. This revision will not retro-fit back to any previous models. Doing do so will produce an overdrive solenoid electrical fault. An un-expecting tech not knowing this change can be sent off on an unnecessary diagnostic routine thinking of wiring problems. After all, the solenoid assembly is new.

To keep out of trouble, here is what you need to know. The early solenoid body had a black connector. There were revisions made to this solenoid body in 2004 which can be identified by a white connector. Sometime in 2009, the valve body casting was anodized and it was fitted with the white style solenoid body and sold as a set for the 68RFE (part No. 68033980AC). For 2011, the re-designed solenoid body went into production which now is grey in color. This new solenoid body can only be purchased with the valve body as a set for around $360 (part No. 68033980AD).

The new style solenoid body cannot retro fit back to any previous models otherwise you will encounter the OD solenoid circuit error code. However, if you need to change this solenoid body, instead of buying the combo set for 360.00, the earlier white solenoid body will work on all new models (part No. 52119435AF).

The Aisin Seiki AS68RC is another unit with a few interesting issues of its own. This unit may come into the shop with the K2 clutches incinerated compromising fourth, fifth and sixth gears along with an overheated torque converter. The stator inside the torque converter is supported by the transmission pump’s stator shaft via a one-way clutch device called a sprag. During takeoff, there is enough of a force being placed on this stator that the spline in the pump securing the shaft strips causing the shaft to turn. 

Once the shaft turns, the pressure used to apply the K1 clutch for first through fourth gears intrudes into the K2 clutch circuit. This causes the K2 clutch to burn out as they are being partially applied incorrectly. The turning of the stator shaft also compromises the converter charge circuit causing it to overheat. It is possible to have a machine shop restore the shaft to its proper position and to prevent it from turning again by fabricating a key way. This will reduce the cost of repair considerably as a pump can only be purchased in conjunction with a valve body due to updated calibration reasons.

A Final Issue
The last issue to mention relates to modifications. Diagnosing and repairing diesel engines is without question a field of its own. In fact, this field has become so increasingly more sophisticated and technical that there is a shortage of good qualified diesel techs causing a need for one to be in high demand. This doesn’t stop novices from playing around with modifications to unleash some of that potential horse power being held back by a number of reasons, due to a number of reasons. Everything from the air intake, air temperature, fuel injectors and exhaust all can be modified for increases horsepower. This includes modifying the computer strategy as well.

There are some companies that will sell a tuner kit which can be programmed into the computer through the ALDL. When it comes to the 6.7L diesel engines, this will only work with full chassis vehicles equipped with the 68RFE transmission. When a program like this is installed in the incomplete chassis with the AS68RC transmission, it locks the computer’s ability to maintain shift adapts. Upon initial programming the transmission shifts may feel firm due to the increase in horsepower.

But in time the shifts get softer and can lead to premature failure of the transmission. Then, after a rebuild or an exchange, you have a poorly shifting transmission on your hands. You than decide to have a factory scan tool reset shift adapts – great idea. That is when you discover that not even a factory scan tool can re-set shift adapts.

This program modification has the tune control locked but you do not know this. In fact, it might lead you into thinking the computer is faulty so you decide to change it. Once it’s changed, you are happy to see that the shift adapts can be re-set determining that it was the right diagnosis.

Now that the transmission is shifting correctly, you deliver the vehicle to the customer. He realizes the new computer does not have this modification so what do you think he is going to do when he returns home? We know that whenever diesel vehicles are modified to provide increase horsepower, the transmission should also be modified to accommodate this increase in power. But here is a scenario that no transmission modification can guard against. Without having this knowledge, it can be quite a dodge diesel transmission dilemma.

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