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Tackling a 4ET50 Hybrid – Gears Magazine
In Front of the Flywheel - June - 2017

Tackling a 4ET50 Hybrid

Many transmission technicians are hesitant to tackle hybrid and electric transmission repairs. But those repairs may not be as difficult as you might think.

As with all repairs, the first time you work on a specific unit, you’ll want to be extremely careful not to make a mistake. With hybrid/electric applications, you also need to pay close attention to the safety aspects of the repair process.

GM uses the 4ET50 (RPO MKA) in the Chevrolet Volt and the 4ET55 (RPO MKD) in the Cadillac ELR. They switched to the 5ET50 (RPO MKV) hybrid/electric transmission for 2016-and-later Chevrolet Volt and Malibu applications.

The Volt equipped with the 4ET50/5ET50 is classified as an Extended Range Electrical Vehicle (EREV). This type of hybrid/ electric vehicle uses a gas engine to help extend its driving range. The Volt uses electric drive motors mounted in the transmission. The gas engine charges the battery through one of the transmission drive/generator motors.

Yes, the vehicle and its systems are high tech, with multiple controllers; four, high-speed CAN bus communication systems; two DLC connectors; and three separate cooling systems. Keeping that in mind, GM has done everything possible to make diagnosis and repair very technician friendly. System diagnosis is supported by more DTCs than any other GM vehicle. Scan data support parameters are very complete and easy to use.

The transmission consists primarily of

  • a torque dampener assembly
  • a G-rotor main pump
  • an electric auxiliary pump
  • one planetary gearset
  • two rotating clutch assemblies
  • one stationary clutch assembly
  • a valve body with TEHCM
  • two, 360-volt, 3-phase AC electric drive motors/generators

Drive motor/generator A (1) is 55kW and drive motor B (2) is a 111kW unit. (Figure 1)

These systems have four modes of operation possible:

  • Electric only (Motor B) Engine Off — The 1-2-reverse clutch is applied (holds the planetary ring gear). Drive motor B drives the vehicle.
  • Electric only, Engine On — Drive motor B drives the wheels, motor A charges the battery: the 1-2-reverse clutch holds the planetary ring gear while the 1-3-reverse clutch connects the transmission to the engine through motor/generator A.
  • Electric combined, (Motor A and Motor B) Engine Off — The 2-3-4 clutch is applied, connecting drive motor/generator A to the transmission planetary. This allows drive motors A and B to drive the vehicle.
  • Engine On combined; Motor B and Motor A drive the vehicle — The 1-3-reverse and 2-3-4 clutches are applied. Drive motors A and B drive the vehicle while the engine charges the battery.

As in many other vehicles, the driver can select various driving modes by pressing a button on the driver information center (DIC). The driver can choose the preferred driving mode based on operating conditions. These modes include:

  • Normal — The normal mode maximizes the battery charge and use mileage.
  • Sport — The system releases more current during acceleration to make the vehicle more responsive to accelerator pedal input.
  • Mountain — The system maintains a reserve charge for climbing hills by running the engine to keep the battery charged.

Like other hybrid and electric drive vehicles, the Volt offers you the opportunity to expand the type of services you offer and add to your bottom line. Shops are starting to pop up around the country specializing in hybrid and electric vehicle repairs. Few transmission shops are offering to service these vehicles, which may be a lost opportunity.

Remember, this type of vehicle has a transmission; it’s just a little different than the transmissions you’ve serviced for years. Back in the early 90s, everyone was afraid to work on the new electronic transmissions. This is really no different. It’s time to jump into hybrid/electric transmission service with both feet!

Let’s look at a very common repair for the 4TE50/4ET55 transmissions. One of the common issues with this unit is a scraping noise whenever the drive wheels are turning. The noise is more apparent at low speeds and during regeneration or deceleration mode.

The noise is usually caused by a failed drive motor B support bearing. This repair doesn’t require removing the transmission and it’s fairly straightforward.(Figure 2)

Safety Considerations

Before working on any electric or hybrid vehicle, you’ll want to disable the electrical system. Remove all jewelry and watches and always use personal protective equipment such as safety glasses and high-voltage, class-0 insulated gloves, which are available from your local parts supplier or electrical supply warehouse. As always, refer to the factory manual for information regarding disabling the high voltage system.

Next, you’ll want to disconnect the vehicle’s 12-volt battery. Then disconnect the high voltage disconnect plug, located in the center console armrest area. Wait five minutes or more for the capacitors in the inverter to discharge. (Figure 3)

Check the resistance at high voltage terminals A and B as outlined in the factory service information. With the high voltage disconnect plug removed and stored in your toolbox, take some UL-approved electrical tape and cover the hole for the plug.

At this point, you’ll need to disconnect the inverter electrical plug to isolate the inverter from the system. Measure the voltage at terminals A and B of the inverter harness as outlined in the shop manual. The voltage at each point should be less than 3 volts. As always, make sure you’re wearing high-voltage, class-0 insulated gloves and following the shop manual steps while making the vehicle safe to work on.

Bearing Replacement

Once you have the electrical system disabled, you’ll need to remove the transmission side cover. With this application, you don’t need to remove the axle shaft or any suspension parts to access the cover. Removing the side cover will expose the bearing, which is mounted to the rotor of drive motor B.

To remove the side cover you’ll need to:

  • Support the engine with a sling or engine support fixture.
  • Remove the 3-phase cable brackets and reposition the cables as needed.
  • Unhook the shift cable and bracket and move the cable out of the way.
  • Mark the transmission mount position and remove the mount bolts.
  • Remove the wheelwell liner.
  • Lock the steering wheel in the straight-ahead position, and remove the steering intermediate shaft.
  • Disconnect the stator/drive motor electrical connectors.
  • Drain the transmission fluid.
  • Disconnect the stabilizer link from the strut assembly.
  • Remove or tilt the cradle.
  • Remove the side cover.
  • Use a narrow jaw puller and a bridge to remove the bearing from the rotor.
  • Inspect the side cover bushing for evidence of damage. If the cover bushing, bearing mounting area, or resolver (stator position sensor) are damaged, you’ll also need to replace the side cover, and replace or transfer the resolver from the old cover. (Figure 4)
  • Install a new bearing onto the rotor using the appropriate tools. Make sure to place the side of the bearing with the part number facing your bearing driver tool. Drive the bearing into its bore until the bearing outer race is 0.95–1.2mm (0.037”–0.047”) below the bearing bore. (Figure 5)

As you can see, the repair isn’t difficult. If the transmission is contaminated with metal, you’ll need to flush the cooler, just as you would any other transmission. Once the repair is complete, you’ll need to:

  • Connect, install, and reposition the components you disturbed during disassembly
  • Refill the unit with Dexron VI fluid
  • Reinitialize the system
  • Clear the DTCs …and reset the adapts prior to road testing.

A lot of people would like the hybrid and electric car market to disappear, but according to a 2017 AAA survey, “the demand for electric cars may be as robust as it is for pickup trucks.” This was based on a survey of 1,004 adults in February 16-19.

Reasons for interest in electric cars vary:

87% — concern for the environment
62% — lower long-term costs
52% — cutting-edge technology
29% — carpool lane access
12% — other

As you can see, this technology is likely to be around for quite some time. Maybe it’s time for you to make some money from these high-tech vehicles. Now’s the time to educate yourself on these systems and start advertising your services.