This article will highlight portions of a seminar I presented concerning shops that choose to service, repair, rebuild or replace hybrid transmissions. The introduction to this edition of POWERTRAIN PRO, called “Hybrid Transmissions,” is in many respects a part one to this article. So if you haven’t read it yet, please take a moment and give it a read; it will enhance the intended purpose of this article.
For the shops that are resolved to learn how to safely service hybrid vehicles and remove, repair, rebuild or replace non-HV transmissions, let’s begin with fluids. It is imperative to use correct fluids when servicing hybrid vehicles.
Fluids
Attending a hybrid seminar, the speaker spoke of an incident that occurred with a 2004 Toyota Prius. A shop serviced the vehicle by changing the engine oil and filter. It came back with a code P3191, which is an “Engine does not start” code. A further understanding of this code listed under typical malfunction thresholds reads as follows: “Engine start no-determination time (receive from HV ECU) – 100 engine revolutions or more, and 6 seconds or more (varies with engine coolant temperature).” This suggests that the computer is looking for the speed in which the engine should start at. If that threshold is not met, the code sets.
Long story short, the vehicle calls for SAE 5W-30 and a heavier weight was used, thus slowing down start up time (ambient temperature related). Toyota issued a TSB on this as well (EG050-04). The point here is the importance of using correct fluids.
Ford uses a system similar to this design and requires a specific coolant. There are reports that if incorrect coolant is used, there are some that have an adverse chemical reaction to the transmission’s aluminum case. The case becomes damaged by oxidation, requiring transmission replacement. This could set a shop back by about $7,000.Another example along these lines has to do with the inverter system. The inverter is used to convert DC voltage from the high-voltage (HV) batteries to AC voltage with which to operate a motor-generator. Likewise, it can convert AC voltage generated by the motor-generator to DC voltage to charge the HV battery. The inverter typically is under the hood, and the motor-generators typically are inside the transmission. The heat that is produced requires the need for the motor-generators to have its own cooling system.
Originally, the fluid was green (1999-2002), then changed to yellow (2002-2011) and now is orange (2011 to present). Ford’s yellow MECS coolant is Motorcraft Premium Gold Engine Coolant U.S. part No. VC-7-B (specification sheet WSS-M97B51-A1). The orange is Motorcraft Orange Antiefreeze/Coolant Prediluted (specification sheets WSS-M97B44-D or D2).
One final example of fluid caution, internationally, Ford had used a variator and push belt type CVT transmission called a CFT30 in the Five Hundred, Ford Focus, Freestyle, Taurus, Montego and Sable vehicles. Ford’s hybrid vehicles began using a transmission called the P310 transmission, but is commonly referred to as the eCVT. This brings up confusion as to the type of transmission fluid to be used. The eCVT uses Motorcraft Mercon LV Automatic Transmission Fluid (XT-10-QLVC). This is not to be confused with the continuously variable chain type transmission fluid XT-7-QCFT (blue in color). Operational issues and internal damage will occur if used.Correct fluid levels need to be mentioned here, as changing the coolant in this system is not as easy as one might think. That is unless you use a vacuum fill system to eliminate possible trapped are pockets falsifying a full fill.
Hybrids are a different type of vehicle, and by looking at three examples, one with engine oil, motor electronic coolant and transmission fluid, a successful servicing in these areas will require specified fluids.
The transmission in the BMW ActiveHybrid 7 is quite similar in design. This is a ZF8HP70 transmission with a hydraulic torque converter and converter clutch being driven by either a gas engine or electric motor.Non-HV Transmissions
Mild hybrids, such as Honda and some BMWs, use non-HV transmissions. A typical Honda hybrid configuration uses a gas engine and an Integrated Motor Assist (IMA) motor to provide torque input through a dual mass flywheel into the transmission. The transmission is nothing more than a typical push belt CVT transmission. It is very similar to the CVTs that Honda uses in its non-hybrid gas vehicles.
These two transmissions serve as a great example for the type of shop willing to learn how to safely work on hybrids so as to repair, rebuild or replace non-HV transmissions. It’s just a matter of safely powering down the HV system and pulling the unit. The Honda CVT is known for start clutch failure, while the ZF8HP units are known to experience A clutch failure. In fact, I recently tore down a ZF8HP70 and a ZF8HP45 at the ALTO plant in Atmore, Ala. They were two completely unrelated transmissions brought in from different parts of the country with the exact same damage. So these two mild hybrid vehicles with non-HV transmissions can be nice work for a shop when they fail.
Keeping in mind the motor-generators, the inverter and the HV batteries function together as a unit. It is the core of the hybrid system. To diagnose and repair, rebuild or replace the HV batteries also requires being able to do the same with the inverter and motor-generators for they go hand in hand. As a result, to work with HV transmissions requires a completely different level of commitment and dedication when compared to working with non-HV transmissions.HV Transmissions
As mentioned in the introduction of this POWERTRAIN PRO Supplement, there basically are two types of HV transmissions: GM’s two-mode transmissions, which use clutch pack assemblies and motor-generators internally, and Ford and Toyota, which use only motor-generators in conjunction with a power splitter. In either style, three phase HV wires run directly into these transmissions.
In short, to be able to tackle a HV transmission, you are committing yourself to being a full-fledge hybrid specialty shop. This will require an investment of time and money in both education and diagnostic equipment.
If one of these clutch assemblies fails, say the 1-3 clutch (1st and 3rd), there will be an issue shortly after the initial launch of the vehicle. The vehicle will begin to move forward on electric power using Drive Motor Position 1 while applying hydraulic pressure to the hybrid low 1-2 clutch. You might notice a shudder sensation during the launch. Then at some point should there be a need to switch to an Internal Combustion Engine (ICE) driven 1st gear, the 1-3 clutch will need to be applied. If it is failed, a neutralizing will take place on top of the switch from electric to gas power.To attempt to work on only one part of the system with out having the understanding of the entire system could get you in trouble. This could easily happen with a GM two-mode transmission. Using the 2ML70 RWD version as an example, this transmission uses four clutch pack assemblies in combination with motor-generators (for greater details and photos, see the “Introduction to GM’s Two Mode Hybrid Transmission” dated Jan. 2, 2013, at MotorAge.com/POWERTRAINPRO). The four clutch assemblies are a hybrid low 1-2 clutch, a 1-3 clutch, a hybrid direct 2-3-4 clutch and a 4th clutch. The two motor-generators are identified as Drive Motor Assembly 1st Position and Drive Motor Assembly 2nd Position.
With only thinking that there is just a failed clutch issue, the transmission might be removed to rebuild the clutch packs. Upon disassembly, the Drive Motor Position 1 comes out first followed by the 1-3 clutch assembly. The Drive Motor passes a visual inspection and the 1-3 clutch assembly is confirmed to have been compromised. The transmission now undergoes all necessary repairs and is installed back into the vehicle. A road test reveals a continued shudder on an electric launch, yet a good 1st gear switch over to ICE, at which time the shudder goes away. Now what? Is it a bad Drive Motor, a problem with the inverter, the HV batteries or is there something wrong with the hybrid low 1-2 clutch? Without knowing how to diagnose the HV system (or having the equipment to diagnose with) the shop now finds itself in a very uncomfortable position.
Now, let’s take a look repairing only one aspect of the hybrid system from a completely different perspective. A shop only rebuilds HV batteries, but has no interest in dealing with the motor-generators inside the transmission. What will that shop do if the motor-generators are about to have a problem? After battery reconditioning or rebuilding, a month later a motor-generator goes down. The owner certainly will try to hold the shop responsible for this failure. There is no doubt that by making repairs to only one aspect of the hybrid system can be risky. If there are multiple issues beyond your repair and expertise, it can be quite a set back.
It is for these reasons I believe that some shops will never work on hybrids. Others will learn to service them and handle the non-HV transmissions. While others will invest what it takes to handle the entire hybrid system, there might be big opportunity with city and local governments that have gone green with their vehicle fleets.
For those that are considering making such an investment, a couple of places to visit for equipment and training would be ALL-TEST Pro, LLC with its AT33EV Motor Circuit Analysis Tool and Automotive Research and Design with its Battery Testing and Analysis Kit called the BDUGENIII. These are specifically designed high-end pieces of hybrid diagnostic equipment that do a thorough job in checking the motor and batteries. They also offer training needed to use these tools effectively.
There are several other reputable organizations that offer hands-on training such as ATTS in Mahopac, N.Y. They offer a three-day, hands-on class called “Understanding and Diagnosing Hybrid Vehicles.” So there is training and equipment available for those who choose to go all the way.
The days of working in a transmission shop have drastically changed over the past 10 years. Shops are increasingly face-to-face with continuously variable transmissions, dual clutch transmissions, sequential shift transmissions, hybrid non-HV and HV transmissions as well as fully computer controlled 8, 9 and 10 speed FWD and RWD transmissions. It’s getting tough to determine what a shop will decide to work on and not work on. The comfort zone of having plenty other familiar work is being threatened by the use of these other types of transmissions occupying the streets. Because hybrids appear to be at the bottom of the list for many, it might be good to at least learn about how they work. Understand the systems and become familiar with them. Not knowing them is often times the reason a decision is made to not work on them. Learning them could equate to increased revenue and customer service.
Subscribe to Motor Age and receive articles like this every month…absolutely free. Click here
