Other Articles - January/February - 2018

8L90 Solenoid Strategies

Solenoids have come a long way since the early, on/off styles. From regulation to clutch control, these solenoids are becoming not only the norm, but every year there seems to be something new.

In this issue, we’re going to cover the 8L90 solenoid strategy and operation. This is similar to what Ford does with the 6R140W, also known as the Torqshift 6. They’re using each individual solenoid to control its own separate component.

To do this, you have to identify the solenoid and match it with the TCM strategies. A part unique number (PUN) is located on the valve body and solenoids (figures 1 and 2) and a transmission unique number (TUN) is located on the case (figure 3).

These part numbers identify the solenoid unique performance characteristic data, which is stored in the transmission control module (TCM) as part of the TIS2 Web Service Programming System (SPS).

If you change the transmission, valve body, solenoids, or TCM during a repair, you must download the unique performance characteristic data from the web server and reprogram the TCM for the system to function at maximum efficiency.

You can reprogram the solenoid characterization using capable laptop software to access the TIS2Web Service Reprogramming System. You can also reprogram the solenoid characterization to refresh the unique performance characteristic data in the TCM.

Here’s how:

  • Document the new part unique number (PUN) or the transmission unique number (TUN) as required.
  • Log into the TIS2Web/SPS web site and enter the vehicle identification number (VIN).
  • Select transmission control module programming.
  • Select the applicable service procedure and provide the TUN or PUN required.

The system will read the vehicle identification number from the ECM using GM’s Multiple Diagnostic Interface (MDI) and then retrieve the applicable data tree through the internet. The data tree accesses the original characterization data so it can update the component information.

The system acquires the characterization data for the new PUN/TUN and updates the genealogy tree. It then updates the TCM with the correct solenoid characterization data and updates the web with the new genealogy strategy.

There are nine solenoids on the 8L90 valve body (figure 4): seven variable force pressure control (PC) and two on/off solenoids. The 1-2-7-8-reverse (S1), 2-3-4-6-8 (S4), 4-5-6-7-8-reverse (S5) and line pressure solenoids are normally high (NH).

 

The TCC, 1-3-5-6-7, and 1-2-3-4-5-reverse are normally low. These solenoids are controlled by current flow and all measure 4.5–5.5 ohms. The only two, three-port, on/ off, normally closed (NC) solenoids are the default control (S8) and the 1-2-3-4-5-reverse boost (S9) solenoid.

The chart (figure 5) shows the location of the solenoids by the casting letter embossed on the valve body. The only missing casting letter is B. Some manuals show the information for the last two solenoids in the opposite locations, which is incorrect.

The two, three-port, on/off, normally closed shift solenoids — S8 and S9 — are also referred to as normally low solenoids. The S8 fault control shift solenoid controls the default override valve. The S9 1-2-3-4-5 reverse boost shift solenoid controls the 1-2-3- 4-5 clutch boost valve (figure 6).

These solenoids are the same and can easily be interchanged. When the solenoid is off, control pressure exhausts from the back of the solenoid. Supply pressure (actuator feed limit) is blocked at the solenoid. When the solenoid is on (provided ground by the TCM), it blocks the exhaust port and opens supply pressure to the control pressure circuit.

In simple terms, it works like this:

  • Off/On — Solenoid control port isn’t pressurized at low speed in 1st gear; solenoid control port is pressurized at high speed in 1st gear.
  • On/Off — Solenoid control port is pressurized at low speed in 2nd gear, solenoid control port isn’t pressurized at high speed in 2nd gear.

The default valve is hydraulically latched in the stroked position in this state; the default solenoid can be commanded on for lube override.

There are four, normally high, pressure control solenoids: the S1 (1-2- 7-8-R), S4 (2-3-4-6-8), S5 (4-5-6-7-8- R) and line pressure control solenoid. When these solenoids are off, they provide pressure to stroke the clutch control valve, allowing controlled line pressure into the apply clutch circuit (figure 7).

When turned on, the solenoid shuts off pressure to the control valve (stationary), which blocks line pressure from entering into the clutch apply circuit. The solenoid accumulator keeps the solenoid signal pressure smooth. The TCM controls both the power and ground circuits.

Although these solenoids work the same way, each has a different part number and provides different flow rates, so always install them in their original locations.

There are three, normally low, pressure control solenoids: The S2 (1-2-3-4-5-R), S3 (1-3-5-6-7), and S7 (TCC pressure control solenoid). When these solenoids are off, they prevent pressure from reaching the control valve (stationary), blocking line pressure from entering the clutch apply circuit (figure 8).

When turned on, they provide pressure to stroke the clutch control valve, allowing controlled line pressure into the apply clutch circuit. The solenoid accumulator keeps the solenoid signal pressure smooth. The TCM controls both the power and ground circuits.

Although these solenoids work the same way, each has a different part number and provides different flow rates, so always install them in their original locations.

For a quick understanding of the solenoid and clutch operation, refer to the Solenoid Operation Chart and the Clutch Apply Chart (figures 9 and 10).

If you have to replace the solenoids or valve body, or reprogram the system, always perform the adaptive relearn. If you don’t, you could run into harsh or erratic shifting.

This can occur if the vehicle has been repaired or reprogrammed without an adaptive relearn. This can cause the calibration to over-adjust the shift parameters. Run a service adaptive relearn procedure to reset the calibration to baseline parameters.

Before performing the procedure:

  • Always install the most recent GDS2 (Global Diagnostics System 2) update.
  • If the transmission fluid temperature isn’t between 75ºC (167ºF) and 85ºC (185ºF), the scan tool won’t allow you to perform the service fast learn procedure.

Here’s how to perform the adaptive relearn procedure:

  1. Drive the vehicle to warm transmission fluid to between 75ºC (167ºF) and 85ºC (1 85ºF).
  2. Connect the MDI (Multiplex Device Interface) to the vehicle.
  3. Access GDS2 and navigate to the Transmission Adaptive Values Learn screen using the following GDS2 navigation path: Diagnostics > Global Vehicle Selection > Module Diagnostics > Transmission Controls > Configuration/Reset Functions > Transmission Adaptive Values Learn.

    IMPORTANT — After performing the Transmission Adaptive Value Learn procedure, shut the ignition off for at least two minutes to make sure the transmission control module shuts down completely before driving the vehicle. This reboots the transmission control module, which is necessary for the transmission control module to operate under the new learned values.

  4. Follow the Transmission Adaptive Values Learn on-screen instructions. Refer to the Transmission Service Fast Learn Procedure in SI if required.
  5. Remove MDI from the vehicle.
  6. Verify transmission shifts into reverse and drive.

I’m sure solenoid strategy will change again and again as time goes on; staying on top of those changes will keep you in the game for a long time to come. Until next time…