Transmission Outputs

Shift Solenoids 

6F15 has 5 shift solenoids:

• SSA - a Variable Force Solenoid (VFS) that controls CB1234 (a brake clutch, grounds an element to the case, that is on in 1st, 2nd, 3rd and 4th gear)
• SSB - a VFS that controls C35R (a rotating clutch on in 3rd, 5th and Reverse)
• SSC - a VFS that controls CB26 (a brake clutch on in 2nd and 6th gear)
• SSD - a VFS that controls either CBLR (a brake clutch on in 1st gear with engine braking and Reverse) or C456 (a rotating clutch on in 4th, 5th and 6th gear)
• SSE - an On/Off solenoid that controls the multiplexing of SSD between CBLR and C456.

Output circuits are checked for opens, short to ground and short to power faults (codes listed in that order) by the PCM by monitoring the status of a feedback circuit from the output driver (SSA P0750, P0973, P0974; SSB P0755, P0976, P0977; SSC P0760, P0979, P0980; SSD P0765, P0982, P0983; SSE P0770).

The shift solenoids are also functional tested for stuck on and stuck off failures. This is determined by vehicle inputs such as gear command, and achieved gear (based on turbine and output speed). In general the shift solenoid malfunction codes actually cover the entire clutch system (solenoid, valves, and the clutch itself since using ratio there is no way to isolate the solenoid from the rest of the clutch system), BUT due to the hydraulic controls arrangement on 6F it is possible to isolate two specific solenoid failures from clutch system faults:

• SSB stuck on from C35R stuck on - due to hydraulic interlock between CBLR and C35R we can isolate SSB stuck on from C35R by turning SSE on in 1st gear without engine braking (get 1st if SSB stuck on, get 3rd if C35R is stuck on)
• SSD stuck off. Since SSD is multiplexed (controls both CBLR and C456) we can isolate CBLR stuck off and C456 stuck off from SSD stuck off since the latter impacts both clutch systems.

For SSA thru SSD Diagnostics will isolate the fault into clutch functionally (non-electrical) failed off (SSA P0751, SSB P0756, SSC P0761, SSD P0766) and clutch functionally failed on (SSA: P0752, SSB: P0757, SSC: P0762, SSD: P0767). The On/Off solenoid (SSE) controls the multiplexing of SSD between CBLR and C456 clutches. Using ratio we can determine if the multiplex valve is in the wrong position, but cannot be sure if the failure is due to the solenoid or a stuck valve. The multiplex valve is tested for stuck in default position (P0771, includes SSE stuck off) and stuck in spring compressed position (P0772, includes SSE stuck on) failures.

Gear ratio errors: 

If ratio errors are detected that do not match an expected pattern for a failed solenoid then gear ratio error fault codes (1st gear - P0731, 2nd gear - P0732, 3rd gear - P0733, 4th gear - P0734, 5th gear - P0735 or 6th gear - P0729) will be stored.

Torque Converter Clutch 

The Torque Converter Clutch (TCC) solenoid is a Variable Force Solenoid. TCC solenoid circuit is checked electrically for open, short to ground and short to power circuit faults internally in the PCM by monitoring the status of a feedback circuit from the output driver (P0740, P0742, P0744).

The TCC solenoid is checked functionally by evaluating torque converter slip under steady state conditions when the torque converter is fully applied. If the slip exceeds the malfunction thresholds when the TCC is commanded on, a TCC malfunction is indicated (P0741). If the TCC is stuck on when commanded off in multiple gears a fault code is stored (P2758).

For 6F15 the TCC is controlled by a 2 valve system - TCC reg apply and TCC control valve. Normally the TCC VFS controls the positions of these valves - turning on the TCC VFS moves both valves from the release to the apply position. If the TCC control valve sticks in the apply position then there will be no flow thru the TCC (both apply and release sides exhausted) when commanded open, which will cause the converter to overheat.

A method to detect this failure was designed into the hardware - SSE pressure is routed to the TCC reg apply valve (SSE has no effect on TCC control valve). In 3rd gear or higher if TCC is open SSE can be turned on, moving the TCC reg apply valve to the apply position. If the TCC control valve is in the wrong (apply) position this will cause the TCC to apply. If the TCC applies when SSE is turned on in 3rd, 4th, 5th or 6th gear while TCC is commanded open (TCC VFS pressure low) the failure will be detected, a P2783 DTC fault code stored. Even though this test only detects failures of the control valve, the FMEM actions alter the shift and TCC lock schedules to keep the TCC applied as much as possible, so this failure has been made MIL.

Electronic Pressure Control 

The EPC solenoid is a variable force solenoid that controls line pressure in the transmission. The EPC solenoid has a feedback circuit in the PCM that monitors EPC current. If the current indicates a short to ground (low pressure), a high side switch will be opened. This switch removes power from all 6 VFSs and the on/off shift solenoid, providing Park, Reverse, Neutral, and 5M (in all forward ranges) with maximum line pressure based on manual lever position. This solenoid is tested for open (P0960), short to ground (P0962), and short to power (P0963) malfunctions.

High Side Switch 

6F15 has a high side switch that can be used to remove power from all 7 solenoids simultaneously. If the high side switch is opened, all 7 solenoids will be electrically off, providing Park, Reverse, Neutral, and 5M (in all forward ranges) with maximum line pressure based on manual lever position. The switch is tested for open faults (switch failed closed will provide normal control). If the switch fails, a P0657 fault code will be stored.

ADLER (chip that controls all 7 solenoids) diagnostics: 

The solenoids are controlled by an ADLER chip. The main micro sends commanded solenoid states to the ADLER, and receives back solenoid circuit fault information.

If communication with the ADLER is lost a P1636 fault code will be stored. If this failure is detected the states of the solenoids are unknown, so the control system will open the high side switch (removes power from all the solenoids), providing P, R, N and 5M with open TCC and max line pressure.

TRID Block 

The TRID block is a portion of flash memory that contains solenoid characterization data tailored to the specific transmission to improve pressure accuracy.

The TRID block is monitored for two failures:

• TRID block checksum error / incorrect version of the TRID (P163E)
• TRID block not programmed (P163F)

If the TRID block is unavailable FMEM action limits operation to 1st and 3rd gear until the issue is correct.