Saab 55-50/51SN Electronic Functions

Valve Body Xpress

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Electronic Control System

The transaxle is controlled by a transmission control module (TCM). The TCM uses inputs from the shift lever module (SLM), transaxle fluid temperature sensor, input/output speed sensors, gear selector position sensor, steering wheel switch unit and other inputs from the bus communication.

The TCM outputs include five shift solenoids, a PWM lock-up solenoid, a PWM transmission pressure solenoid and a PWM shift pressure solenoid. Shift solenoids are on/off type and PWM solenoids operate at 300Hz. Solenoids are powered by the TCM and ground through casing of the solenoid to the valve body.

When the TCM detects a serious problem, it:

  • sets a trouble code.
  • sends a "CHECK GEARBOX" bus message.
  • sets an indicator lamp in instrument cluster.
  • shuts power off to shift and pressure solenoids.

This puts the transmission in "limp-in" mode, allowing only 5th gear in the D-range and Reverse in the R-range. NOTE: 2nd gear can be selected in M-range on some models.

The TCM is reprogrammable and uses an EEPROM to store memory functions/trouble codes. Disconnecting power to the TCM will NOT clear codes or reset shift adapts. The Tech 2 Scan Tool or equivalent must be used to clear codes or reset shift adapts. In addition, if the TCM is replaced - and sometimes after reprogramming - Tech 2 must be used to "marry" the TCM to the vehicle so other modules can communicate.


Alternate Shift Programs

  • Manual Shifting - can be accomplished by moving the manual shift lever to the "M" position, whereby you can control up/downshifts using + and - buttons on the steering wheel. The TCM overrides manual controls if engine RPMs get too high and shift has not been commanded by the driver, or if the driver forgets to downshift when the vehicle speed drops below threshold for the selected gear. The TCM will not allow the driver to downshift the vehicle manually until vehicle speed drops below the predetermined point for a particular gear. The driver can start from a stop in 1st, 2nd or 3rd. The manual feature can even be used with cruise control.
  • Temperature Program 1 - activated when the transmission fluid temperature exceeds 125°C. Lockup is activated in 3rd and 4th with no converter slip, and shifts are at higher speed to cool transmission fluid. When fluid temperature drops below 120°C, Temperature Program 1 deactivates, and it will not activate when the TCM is in "limp home."
  • Temperature Program 2 - activated when the transmission fluid temperature exceeds 135°C. This forces upshifts at higher speed and converter lockup happens more often than in Temperature Program 1. Lockup is commanded with no slippage. Temperature Program 2 deactivates when transmission fluid temperature drops below 127°C and returns to Temperature Program 1. NOTE: If transmission fluid temperature rises above 155°C for more than 2 seconds, then code P0218 is set, the temperature is recorded, the "CHECK GEARBOX" light does NOT light and the TCM sends a bus message "TRANSMISSION OVERHEATING" in SID display. Engine torque is reduced to a max of 200Nm to protect the transaxle.
  • Gear Change Program - automatically activated if high load is detected. Up/down shifts occur at higher engine speed to keep fluid from overheating. Examples of when this program engages include driving up long hills and trailer towing. NOTE: Will not initiate over 150 km/h.
  • Differential Protection System (DPS) - reduces engine torque during extreme wheel spin. DPS only activates below 80km/h. 150Nm is the maximum engine torque allowed during DPS activation.
  • Reverse Inhibit Feature - turns on the S1 solenoid, which releases the B3 brake if the TCM detects that the vehicle is moving over 7 km/h (4.3 mph).


Resetting Adapts

Using a Tech 2 or equivalent scan tool zeros out shift adapts in the EEPROM. Transmission temperature must be 65-110°C for the TCM to relearn adapts. DO NOT stall test the transaxle to warm it up. The Saab service manual states that 10-15 minutes of varying driving should be sufficient for the TCM to relearn adapts after zeroing with a Tech 2, however, driving the vehicle will not relearn the N-D and N-R adapts.

  • Engagement Relearn - Set the parking brake, and with the engine idling at operating temperature, shift N-R. Keep in R for 3 seconds, then shift back to N. Repeat 5 times and perform the same procedure for D.
  • Up/Down Shift Relearn - NOTE: Always perform engagement relearn first, then perform shift relearn. Put the manual shift lever in D and accelerate to just over 50 km/h at 15-20% throttle angle until the car shifts into 4th. Slow the car to a stop with light brake pressure. It's important that it takes at least 30 seconds to get to 4th gear and more than 14 seconds to stop. Repeat 5 times.
  • Manual Shifting 2nd-1st Relearn - Engage M2 with the shift lever. Accelerate to 25 km/h, then engage M1 and brake smoothly to stop. Repeat 10 times.


Saab Service Bulletins for this Transaxle

  • TSB # 440-2425, January 2004: Springy upshift from 2nd to 3rd or 2-3 slide/slip. This bulletin involves reprogramming the TCM.
  • TSB # 440-2498, October 2004: Hard, delayed or incorrect shifting, rising engine speed during shifting with various symptoms. Depending on the symptoms, the fix could be sensors, software upgrades or internal transaxle repairs.

Related Part(s)
Related Unit(s)
Subject(s) Included
  • General Diagnostics and Theory

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