KEEP THOSE TRANNYS ROLLING
Diagnosing the 2011 Chevrolet Volt 4ET50 Transmission
by Pete Huscher
members.atra.com www.atra.com
I
n the last issue of Keep Those Trannies Rolling, we took a brief look at what makes the 2011
Chevrolet Volt tick. In this issue, we’ll look at the diagnostic routines used to keep the 4ET50 transmission rolling down the road.
A Little Bit about the 4ET50 Transmission The 4ET50 transmission is a fully
automatic, variable-speed, electronical- ly controlled, front wheel drive trans- axle consisting of these components: • torque dampener assembly • main and auxiliary fluid pump • planetary gearset (used for gear reduction)
• two hydraulic clutches • one mechanical clutch • hydraulic control system • two internal electric generator/ drive motor assemblies The generator/drive motor assem-
blies are identified as generator/drive motor A (rated at 55kW) and gen- erator/drive motor B (rated at 111kW). Generator/drive motor A is primarily used to start the internal combustion engine, charge the on-board battery systems, and assist generator/drive motor B with vehicle propulsion when needed. Generator/drive motor B is pri- marily used to propel the vehicle down
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the road. The main transmission assembly is
controlled by the transmission control module or TCM (located on the valve body assembly) and the power inverter module, or PIM (located on top of the transmission assembly). The TCM controls shift timing
and feel by controlling two shift sole- noids, six variable-bleed pressure con- trol solenoids, and a torque dampener pressure control solenoid (all located on the TCM/valve body assembly). The TCM, solenoids, and valve body are only available as an assembly. The TCM is capable of adaptive
learning, which provides consistent shift feel and transmission durability. The PIM controls the two generator/ drive motors, located in the transmis- sion.
The 4ET50 transmission offers
five selectable gear ranges: 1. park 2. reverse 3. neutral 4. drive 5. low Now that we’ve covered the prin-
ciples of how the 4ET50 transmission operates, it’s time to look at how to diagnose and repair the transmission control system.
Diagnosing the 4ET50 Transmission Diagnosing the 4ET50 transmis-
sion electrical system is pretty straight- forward. Before performing any diag- nostic routines on the 4ET50 transmis- sion, always perform a Pre-Diagnostic System Check, which includes: • Verify that the 12V low voltage battery is fully charged.
• Make sure the battery connections are clean and tight.
• Check that the fuses are intact. • Verify that the wiring harnesses and connections are secure.
• Make sure there are no aftermar- ket devices installed that could affect the computer system opera- tion.
Diagnostic System Check Before starting any diagnostic
routine, always perform a Diagnostic System Check, which includes: • Verify the customer’s complaint. • Perform a recall/bulletin search for related problems.
• Determine whether the problem is mechanical or electrical.
• Connect your scan tool and check for codes in all on-board control modules.
• Identify and document any codes. GEARS March 2012
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