282 Automatic Transmissions and Transaxles Copyright by Goodheart-Willcox Co., Inc. Bands and clutches Shift valve Shift valve Bands and clutches Governor valve Throttle valve A ECM Shift solenoids Vehicle speed sensor Throttle position sensor B Figure 12-29. Compare the interaction of the governor, throttle valve, and shift valve in a hydraulically controlled transmission (A) with the interaction of the throttle position sensor, vehicle speed sensor, ECM, and solenoids on an electronically con- trolled transmission (B). Valve body Wire harness Governor pressure sensor Governor pressure solenoid Park rod Figure 12-28. The governor pressure solenoid is placed on the valve body and takes the place of the shaft-mounted governor valve. The assembly also contains a governor pressure sensor. (Chrysler). throttle and governor valves in a hydraulically operated transmission. Other inputs to the ECM also affect shift speeds. For instance, the MAF or MAP sensors may indicate that the engine is under a heavy load, and therefore, the ECM may decide to shift the transmission into a lower gear, even though throttle position and speed sensor inputs call for a higher gear. The ECM may also select a lower gear if the temperature sensor indicates that the engine is beginning to overheat. Other sensor inputs may cause the ECM to raise line pressure or delay the application of the converter lockup clutch. If one of the sensors fails, the ECM is able to make shift decisions based on inputs from other sensors. If, for instance, the throttle position sensor fails, the ECM may make shift decisions based on input from the MAP sensor. In other instances, failure of a sensor may cause the ECM to shift into limp-in mode. In limp-in mode, the ECM can make shifts as soon as possible, eliminate some gears, raise line pressure, or prevent lockup clutch apply. The ECM will also turn on the malfunction indicator light (MIL) on the dashboard to let the driver know there is a problem with the system. Electronic Transmission with Two Shift Solenoids The following section explains how a widely used elec- tronically controlled transmission uses two multi-shift sole- noids to provide four forward gears and reverse. Operation in Neutral and Park is also covered, as well as the application of the converter lockup clutch. This transmission is found on many late-model cars and light trucks. Refer to Figures 12-30 through 12-41 as you read the following paragraphs. You may also compare the operation of this hydraulic system with the operation of the hydraulic system on an older version of this transmission shown in Figures 11-11 through 11-22. When you make the com- parison, note the similarity between the two types of trans- missions. They use the same number and type of holding members for each gear. Some of the hydraulic valves are the same or similar. Park, Engine Running The shift lever is in the Park position with the engine running, Figure 12-30. The pump is turning and supply- ing pressure to the main pressure regulator. Pump pressure is also sent to the pressure relief valve. The main pressure regulator consists of the regulator valve and a boost valve. The pressure regulator spring is installed between the two valves. Line pressure from the pump also passes through the manual valve and the low overrun valve, and applies the low and reverse clutch. The low and reverse clutch has no effect on operation in Park and is only applied because of the valve body and manual valve design.