If you are an experienced technician, you have no doubt had your fair share of run-ins with transmission issues on Dodge trucks fitted with either a 5.9L or 6.7L Cummins diesel engine. If you are not an experienced technician or have not had much exposure to transmission issues on Dodge trucks, you are almost destined to run into a variety of transmission issues on these vehicles as your career progresses. In fact, if you work on Dodge trucks with 5.9L or 6.7L engines at all, there is no way to avoid dealing with the issues that come with their transmissions.
However, unpleasant as that sounds, knowing which transmission you are dealing with goes a long way towards removing much of the guesswork involved in diagnosing these transmissions. Part of the problem is that while successive attempts to correct design flaws had been made, almost every new attempt brought its own, new problems, and in this article, we take a closer look at some of the causes of these transmission issues, as well as how you can avoid falling down diagnostic rabbit holes when diagnosing them. Before we get to specifics though, let us take a look back at-
As stated earlier, knowing which engine/transmission combination you are dealing with makes things somewhat clearer, so here is a summary of the history of these combinations-
Starting in 1998, and continuing until around the middle of 2003, Dodge trucks with 5.9L 24-valve diesel engines were fitted with four-speed rear-wheel-drive transmissions, with the code 47RE. These models also featured separate powertrain (transmission) and engine control modules. Around the middle of 2003, several significant design changes called for an updated transmission, which was given the code 28RE, as a means to differentiate between the two transmission versions. This basic configuration saw service until early in 2007.
When the 6.7L engine was released in 2007, it was fitted to a full chassis truck*. This engine was mated to an all-new six-speed transmission with the code 68RFE, but 6.7L engines that were fitted to trucks with incomplete chassis were mated to Seiki six-speed transmissions with the code AS68RC, and which were manufactured by Aisin.
* Although the terms “complete chassis” and “incomplete chassis” largely mean the same thing in all western automotive markets, the technical definitions of these terms differ somewhat between markets. Refer to this Federal Government resource to learn more about how these terms are defined and applied in the Australian market.
The above summary reflects the principal changes, but many software updates, revisions, or redesigned mechanical and/or hydraulic parts and components had been introduced at various times since 1998. So with this in mind, let us start at the beginning-
The 5.9L/47RE combination began to exhibit severe problems with the shuttle valve that controlled the torque converter/overdrive clutch almost immediately after its release. The principal symptoms included a failure of the torque converter clutch to engage or to disengage, or in some cases, the clutch to engage only halfway.
This issue was mainly caused by noisy electronic signals between the engine and transmission control modules, with noisy signals from the throttle position sensor being the most common. In some cases, this could be overcome by reprogramming the engine control unit as per TSB 18-02-99, while in many other cases, the problem could be resolved by installing noise filters between the engine and transmission control modules.
Other common causes included-
It should be noted that the parts and components listed here need not have been inoperable to cause problems with the torque converter clutch. In most cases, the wiring of sensors and/or parts listed here suffered from a lack of proper insulation, which generated extremely noisy signals. These are only the most common sources of noisy signals; there were in fact, more than thirty possible sources of electronic noise on the early versions of these trucks.
However, the most common cause of torque converter clutch issues by a huge margin was the result of poor electrical contacts in the transmission control modules’ connector, which is hardly surprising seeing that the module was bolted on to the side of the engine, which subjected the electrical connections to both severe vibrations and large temperature swings.
Many of these issues were resolved when the separate TCM was removed in 2003, and the Engine Control Module took over the management of the transmission. While the change we well received by the buying public, it also brought-
Although incorporating the TCM into the ECM was a significant change, the new 48RE transmission included a strategy not previously used on Jeep or Dodge vehicles fitted with –RE series transmissions. For some context, the –RE series of transmissions comprised the 42RE, 44RE, and 46RE transmissions used with some petrol engines, while the 47RE was used exclusively with diesel engines.
In short, this new strategy involved supplying the torque converter clutch with pressurised fluid from the same solenoid that supplied fluid to the second gear clutch, which meant that under some conditions, the torque converter clutch could be activated from as low as second gear to improve puling power at low road speeds. While this new arrangement had some advantages, the problem was that if the first gear solenoid became stuck in the closed position because of either mechanical or electrical issues (as it often did), the torque converter clutch engaged automatically on top of the shift from first gear to second gear.
However, provided that all shift solenoids operate as expected, the torque converter clutch will not be applied unless overdrive is achieved or after third gear is engaged if overdrive had been cancelled. However, an unintended consequence of this new clutch control strategy was that when first or second gear is selected manually, the torque converter clutch is applied to improve pulling power. Thus, if the solenoid supplying second gear failed in the closed position (as it often did), the torque converter clutch remained engaged, causing the engine to stall, which was a major inconvenience, to say the least.
There is more though. Perhaps the biggest failure of this transmission was the fact that when the torque converter clutch was engaged at high road speeds, the solenoid that relieved pressure from the clutch circuit remained partially closed when the vehicle came to a stop. Therefore, because the clutch was still partially engaged, the Engine Control Module recognised the additional load and attempted to compensate for it by increasing the engine speed.
The result was a driver standing on the brakes trying to prevent the vehicle from running into the back of the vehicle in front of him-all while the Engine Control Module is doing its best to defeat the brakes. Drivers who have experienced this phenomenon have variously described it as exhilarating, heart-stopping, and in some cases, in terms that cannot be repeated here.
The only remedy for this condition was the replacement of the overdrive solenoid and the complete internal wiring harness.
One other significant change on the 48RE transmission happened in 2005 when the control cable between the transmission and the throttle pedal was eliminated. The purpose of the cable was to provide the transmission with a signal relating to the throttle opening. While the current method of providing this signal via a computer-controlled motor known as the Transmission Throttle Valve Actuator (TTVA) is an improvement, it also has some drawbacks.
For example, if the Engine Control Module lost its Keep Alive Memory for whatever reason, or the Transmission Throttle Valve Actuator was removed, replaced, or serviced, the actuator has to be reprogrammed in a simple, straightforward procedure that involves turning on the ignition for thirty seconds. During this KOEO period, the Engine Control Module will rotate the actuator to relearn its stop positions, but the problem is that in some cases, you may have to perform the procedure multiple times to make the programming "stick".
Failing to make it “stick” always causes shift issues that vary from harsh, unpredictable, or erratic shifts, to the transmission skipping gears, or even failing to select any gear.
The above barely scratches the surface in terms of listing the issues associated with the 47RE/48RE transmissions, but worse was to follow when their successor was introduced. Let’s look at some-
When the all-new 5.9L Cummins diesel engine was introduced in 2007, it was mated to either the all-new, six-speed 68RFE or AS68RC transmissions, depending on the version of the truck the engine was fitted to. While these new six-speed transmissions did offer some improvements over their predecessors, the truth is that both new transmissions were beset by far too many problems, issues, defects, design flaws, and mechanical shortcomings to list all, or even most of them in an article of this nature. Therefore, we will focus only on the issues and problems that you are most likely to encounter. Let us start with-
Like the mechanically similar 545RFE transmission, the single biggest problem with the 68RFE transmission is the premature (and catastrophic) failure of the overdrive clutch. While there are many possible causes of this issue, the most common causes are either a worn-out bore in the valve body or a defective main-line pressure transducer.
Many thousands of overdrive clutched the world over failed because of these defects, but somewhere between the 2009 and 2010 production years, the transmission received a redesigned valve body. This version of the valve body was anodized to reduce wear in shuttle bores, but more importantly, the integrated overdrive solenoid was eliminated.
In terms of practicalities, the old-style valve body controlled the overdrive clutch via either the Multi Select solenoid or the overdrive solenoid, depending on the position of the Manual Valve. In practice, the elimination of the overdrive solenoid altered the hydraulic control system configuration for both the Manual Valve and the PCM strategy for shift/solenoid control. The effect of this change was that it was a) no longer possible to shift manually from second to first gear, and b) that limp mode was now confined to fourth gear since the option to shift into second-gear limp manually was removed.
While these changes did improve the driving experience somewhat, the problem was that the new, redesigned valve body could not be retrofitted into older transmissions, and attempting to do this will always result in several electrical faults involving the (now dedicated) overdrive solenoid.
So here is what you must know when you run into overdrive clutch failures on 68RFE transmissions-
The original 68RFE valve body featured a black electrical connector, which was changed to white when the valve body saw some design changes in 2004. When the major design change happed in 2009/2010, the anodized valve body was also fitted with a white connector, so be on the lookout for the anodizing, which is the only way to differentiate between the original and new-style valve bodies.
In 2011, the redesigned valve body went into large-scale production, and these valve bodies are all fitted with grey connectors. Note that while the 2011 valve body cannot be retrofitted to any pre-2011 68RFE transmission, the 2004 valve body with the white connector can be fitted to all post-2011 68RFE transmissions without too much trouble, which brings us to-
While this transmission has its own set of dedicated problems, issues, and design flaws, the most common issue you are likely to see on this transmission involves destroyed K2 clutches and a seriously overheated torque converter. In terms of symptoms, the transmission may not be able to select fourth, fifth, and sixth gear.
The principal cause of this issue is directly attributable to the poor design of the torque converter/pressure pump assembly. As a practical matter, the torque converters' stator is supported by the pump's shaft via a one-way clutch, which is supposed to prevent the shaft from rotating during hard acceleration. However, this one-way clutch is generally not up to the task, so when the vehicle accelerates aggressively, and especially from a standing start, the clutch fails, which causes the shaft to rotate violently, which in turn, strips the splines that drive the pump either in the pump or on the shaft.
Under these conditions, much of the pressure that activates the K1 clutches leaks out of its dedicated circuit and enters the circuit that controls the K2 clutches. As a result, the K2 clutches are partially engaged along with the K1 clutches that are fully engaged, so since the K2 clutches are only partially engaged, they overheat and the friction material is virtually incinerated. In addition, the pressure leaking from the K1 clutch circuit also leaks into the torque converters’ charge circuit, which is what causes the torque converter to overheat- sometimes fatally.
If the splines on the shaft are stripped, a competent machine shop can restore it to its previous condition, but instead of cutting new splines, a proper keyway, and a key that engages the pump will usually resolve the problem definitively. While this is an expensive option, it is considerably cheaper than replacing both the pump and the valve body, which can only be purchased as a set to preserve the transmissions’ calibration settings, which brings us to one more thing, this being-
For some people, having an already hugely powerful diesel engine is never enough, and while professional engine tuners typically update/upgrade transmissions to cope with the additional power and torque, amateur engine tuners often forget, or may not know that transmissions in Dodge trucks are in no way designed, or able to cope with added torque.
To many, if not most amateur tuners, anything is fair game in their quest to wring more power from a diesel engine. Air intakes, boost pressures, valve timing, injector volumes, exhaust scavenging, and engine management strategies are often leveraged to ridiculous levels to gain that extra few kilowatts over a competitor, and while these modifications might win a few drag races (often only between traffic lights) Dodge transmissions are not able to handle this kind of abuse for long periods.
This is especially true of engine management tunes that are applied to 6.7L engines. In fact, changing engine management strategies is only possible on full chassis vehicles that are fitted with 68RFE transmissions. However, when advanced engine tuning programs are installed, the ECU loses its ability to maintain its shift point strategies.
Upon initial installation of a non-standard engine management program, the gearshifts might seem to be firmer and more precise, but this is only because of the additional torque acting on the transmission. Over time, and depending on the particular engine management program installed, the transmission will begin to fail in various ways; these failures typically include premature torque converter clutch wear, pressure leaking out of valve body circuits, which affects adjacent circuits, and pressure pump failures.
Eventually, gearshifts become “soft”, unpredictable, or erratic, and the transmission may begin to “miss” some gears. At this point, the customer might want you to reset the shift points but it is also at this point that you discover that not even OEM-level scan tools can reset shift points because the non-standard engine management program had erased the ECU’s ability to relearn shift points.
If you do not know this about 68RFE transmissions, you might be tempted to replace the ECU to fix the shifting issues, so you do just that. In most cases, this will restore the transmissions’ operation to near original levels, so you check to see if you can adapt the transmissions shift points in the new ECU. You see that you can, so you restore the shift points to OEM specs, and you hand the vehicle (which now shifts correctly) to the owner, who immediately notices that his high-performance engine management tune is missing.
You threw it out along with the old ECU, but how were you supposed to know what effect the non-standard engine management program would have, or did have, on the 68RFE transmissions’ programmability?
It’s a rhetorical question, we know, but we have to ask it nevertheless because the moral of the above story is this; before you do anything on a transmission on a Dodge truck with a 5.9L or 6.7L Cummins engine, make sure-
The issues described in this article barely represent the tip of the proverbial iceberg in terms of the number of issues that beset the transmissions we described here. Moreover, the myriad causes that must be considered before drawing any diagnostic conclusions are truly staggering, so unless you are an expert transmission tech, we do not recommend that you attempt a diagnosis on these transmissions unless you have access to OEM-level service information for the specific transmission.
Getting involved with these transmissions can be confusing, time-wasting, and expensive when you get a diagnosis wrong. Nonetheless, at their cores, they are just automatic transmissions, which means that if you approach them with caution and with the relevant service information in hand, it is entirely possible to diagnose and fix most, if not all their issues successfully.
