Gen III PCM control goes beyond the engine to be one of best solutions for electronically controlled 4-speed automatic transmissions. Owners not using the LS1 PCM for engine control must look to the aftermarket for a standalone transmission controller that may cost in excess of $1,000. While many who desire an automatic transmission choose either a 4L60-E or 4L80-E transmission when using the LS-series PCM, others may simply disregard the PCM’s transmission functions and use a non-electronically controlled automatic or manual transmission.
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In general, any automatic transmission can be used in a vehicle where the engine is controlled by a Gen III PCM. For early transmissions, the aftermarket offers simple solutions for an electronic vehicle speed signal and standalone torque converter lockup. Most late-model, electronically controlled transmissions can be fully controlled with the LSseries PCM. For electronically controlled transmissions not compatible with the LS-series PCMs (1993–1995 4L60-E transmissions), the aftermarket offers standalone transmission controllers.
Regardless of automatic transmission choice, tuners usually begin with an LS-series calibration from an automatic transmission vehicle to retain proper engine idle characteristics.
It is wise to consult a professional transmission builder for actual fitment details. With the wide variety of engines, transmissions, flexplates, and torque converters, a mismatch of components can easily be avoided with help from someone with experience.
Transmissions with no electronic control should be fitted with a VSS to satisfy the PCM’s vehicle speed input requirement. Although early transmissions are typically equipped to accept a mechanical speedometer cable, the aftermarket offers electronic VSS adapters that continue to allow the use of the speedometer cable while satisfying the PCM’s VSS input.
Electronic Torque Converter Lockup
The electronic torque converter lockup function for non-electronically shifted transmissions (200-4R and 700-R4) is not compatible with the Gen III PCMs. These transmissions use an ON/OFF solenoid to apply torque converter lockup while the LS-series PCMs provide PWM control to a torque converter lockup solenoid. Fortunately, the aftermarket offers standalone torqueconverter lockup kits for applications where the ECM/PCM cannot control torque converter lockup.
1993–1994 4L60-E Transmissions
The 1993–1994 4L60-E transmissions are not compatible with Gen III PCMs. General Motors introduced the 4L60-E transmission in 1993. In design, this transmission is unique in that the PCM is used to control shift solenoids. Drivability is a seat-of-the pants noticeable improvement compared to the 700-R4; the 700-R4 shifts through the gears by means of a detent cable attached to the throttle linkage and weights and springs in the governor. These early 4L60-E transmissions do not have a TCC PWM solenoid, which was added to the 4L60-E transmission in 1995 to assist in applying torque converter lockup.
1995 4L60-E Transmission
The 1995 4L60-E transmission is not compatible with the Gen III PCM. In 1995, General Motors added a TCC PWM solenoid that was used in combination with the TCC lockup solenoid to assist in smoothly applying torque converter lockup. This update is visually noticeable in the 1995 wire harness as a brown wire that was added to connector cavity U of the 4L60-E harness connector.
1996-Newer 4L60-E Transmissions
The 1996-newer 4L60-E transmissions are compatible with Gen III PCMs. In fact, they are compatible with 1996-newer GM PCMs. In 1996, General Motors changed the operation of the 3-2 downshift solenoid from PWM to ON/OFF operation through a ground path provided by the PCM. The 1995 and 1996 wire harnesses are identical, using 13 cavities of the transmission harness connector.
Other compatible 4L60-E type transmissions include the 4L65-E and 4L70-E. But don’t let the 4L65-E name fool you; this transmission is electronically equivalent to the 4L60-E transmission, receiving little more than one additional planetary gear (five gears total) and several stronger internals for improved strength. The 4L70-E is used with Gen IV ECM/TCM systems and can be found in the Chevrolet Trailblazer. This transmission adds an ISS but it is electronically compatible with Gen III PCMs. Very simply, the ISS output signal is not used (or required) by Gen III PCMs.
Enthusiasts requiring a stronger, electronically controlled automatic transmission may consider the 4L80-E transmission. These were installed in many 2500-series GM trucks and can be controlled with Gen III PCMs. The 4L60-E and 4L80-E transmissions use the same harness connector, but are wired a little differently. Tuners must use either a calibration from a truck that has a 4L80-E or perform a transmission segment swap within the PCM calibration.
6L80 and 6L90 Transmissions
General Motors introduced 6-speed automatic transmissions in certain 2006 performance vehicles (Corvette and Pontiac G8). These transmissions feature a built-in TCM identified as a T43 TCM. It communicates with the ECM through CAN messaging. Without the proper CAN messaging (to and from a Gen IV ECM), these transmissions cannot be used.
At the time of this writing, the aftermarket has not made a standalone controller available for the 6L80 and 6L90 transmissions. With no CAN support, the Gen III PCM cannot be used to control the T43 TCM.
In general, any manual transmission can be used in a vehicle where the engine is controlled by a Gen III PCM. Regardless of manual transmission choice, tuners usually begin with an LS-series calibration from a manual transmission vehicle. It is wise to consult a professional transmission builder for actual fitment details. With the wide variety of engines, transmissions, flywheels, and clutches, a mismatch of components can easily be avoided with help from someone with experience.
The 1999–2002 PCM has been used in the Camaro and Firebird to control two T56 manual transmission functions: skip shift and reverse lockout. The PCM may also receive an input from the CPP switch. These functions are optional and most owners choose to eliminate skip shift.
The skip shift function is controlled by the PCM through a solenoid mounted on the transmission. During certain operating conditions, the PCM requires the driver to shift from first to fourth gear, preventing the driver from shifting into second or third gear. Skip shift settings can be changed within the PCM’s calibration.
The reverse lockout function is controlled by the PCM through a solenoid mounted on the transmission. When the solenoid is energized, the driver can easily shift the transmission into reverse. The PCM allows reverse gear whenever vehicle speed is below 5 mph and prevents the driver from shifting the transmission into reverse above 5 mph. Reverse lockout settings can be changed within the PCM’s calibration.
When loaded with a manual transmission calibration, the PCM expects a signal from a CPP switch. GM trucks and Corvette are set to receive a 12V signal (normally closed). The Camaro and Firebird are set to receive a ground signal (normally closed) to indicate clutch pedal status. This circuit is not used to prohibit the engine from starting; it is used for cruise control function and engine control during shift transitions.
Written by Mike Noonan and Posted with Permission of CarTechBooks
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