Transmission Outputs

Shift Solenoids 

The Shift Solenoid (SSA, SSB, SSC, SSD, and SSE) output circuits are checked for opens and shorts 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, P0985, P0986).

The shift solenoids will be tested for function. This is determined by vehicle inputs such as gear command, and gear. Shift solenoid malfunction codes actually cover the entire clutch system (using ratio there is no way to isolate the solenoid from the rest of the clutch system. Diagnostics will isolate the fault into clutch functionally (nonelectrical) failed off (SSA P0751, SSB P0756, SSC P0761, SSD P0766, SSE P0771) and clutch functionally failed on (SSA: P0752, SSB: P0757, SSC: P0762, SSD: P0767, SSE: P0772). These fault codes replace the P2700 level clutch fault codes previously used since the additional information of the failed state of the clutch adds value for service.

Torque Converter Clutch 

The Torque Converter Clutch (TCC) output circuit is a duty-cycled output that is checked electrically for opens and shorts 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).

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 7 VFSs, 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 

5R110W has a high side switch that can be used to remove power from all 7 VFSs 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.

CAN Communications error 

The TCM receives critical information from the ECM via CAN. If the CAN link fails, the TCM no longer has torque or engine speed information available - the high side switch will be opened. The TCM will store a U0100 fault code if unable to communicate with the TCM.

Requirements for Heavy-Duty Engine Testing 

Beginning in 2005, Ford is introducing a new TorqShift (5R110W) transmission for all HDGE automatic transmission applications. This new transmission uses direct electronic shift control technology (DESC) to actuate transmission mechanisms to achieve the desired gear changes. The DESC architecture requires more extensive monitoring within the PCM of transmission components, speeds, and gear ratios to ensure that the transmission is operating within expected ranges. Without the transmission hardware present during engine dyno testing, the transmission diagnostics will presume a transmission/sensor failure, and default to self-protective operating mode. As in past years, this requires special test procedures to be used during HDGE testing to assure a representative test by simulating key signals typically generated from the transmission system. The methodology used to generate these signals has been modified for the 2005MY.

For dynamometer testing on engines using this new transmission, the function of the previously used simulator box is now incorporated as part of the transmission OBD code included in the power-train control module (PCM). The new simulator strategy expands on the old strategy and uses engine rpm, commanded gear, and manual lever position to model transmission control system responses, e.g. representative, scheduled shift points and torque modulation during shifts. The PCM will enter this 'dyno cert' mode if, at start up, the transmission OBD senses that the seven transmission variable force solenoids, the turbine speed sensor, the intermediate speed sensor, and the output speed sensor are all absent. In this mode, transmission diagnostics are disabled, a MIL code is set, and the PCM generates simulated signals that typically come from the transmission.

During the running of the transient dyno cycle, the engine follows a set path of normalized engine rpm and normalized torque as prescribed in the regulations. This simulator strategy allows the engine to perform this cycle, with the PCM reacting as if the transmission were present and the vehicle were operating on the road, resulting in representative shift events and torque modulation. These shift events follow the calibrated shift schedule, but require the input of specific transmission signals. These signals include Turbine Shaft Speed (TSS), Intermediate Shaft Speed (ISS), Output Shaft Speed (OSS), and Vehicle Speed (VSS). Since there is no transmission hardware, these signals must be simulated. The model for the simulation strategy is based on fixed mechanical gear ratios of the transmission, scheduled shift points; small losses of efficiency in the torque converter, and approximations of transmission characteristics during transition periods (i.e. shift transition between 1st & 2nd gears). Simulated characteristics during shifts are based on extensive experience with real world transmission and vehicle operation. The initial inputs to the simulator are engine speed and transmission lever position (e.g. park, drive), these signals determine the status of the Torque Converter Clutch, and in turn output the TSS. In park, TSS equals engine rpm. In drive with the engine speed less than an approximate engine speed of 1000 rpm, the TSS equal zero. As the engine accelerates (or decelerates), the model ramps the TSS signal to respond as closely as possible to the way the turbine shaft would respond on the road. The TSS in turn, along with the status of the overdrive gear set, is used to generate the ISS. This is based on the commanded gear, and fixed gear ratios. During shift events, the model ramps the ISS signal between gear ratios. Likewise, ISS is then used, with the status of the simpson gear set, to generate the OSS, based on the fixed gear ratios. OSS is in turn used by the PCM to establish commanded gear. VSS is calculated from the OSS, using tire size and axle ratio. VSS is used within the PCM for vehicle speed limiting and as an entry condition to some of the engine on-board diagnostics.

The goal of this new 'simulator' strategy is to ensure proper function of the PCM without transmission hardware. Only the transmission OBD recognizes that the engine is in 'dyno cert' mode, the rest of the transmission control systems react as if the transmission hardware is present and is running normally as it would on the road.