346 Automatic Transmissions and Transaxles Copyright by Goodheart-Willcox Co., Inc. Example: P0712 Transmission Fluid Temperature Sensor Low Input P 0 7 12 B=Body C=Chassis P=Powertrain U=Network 0=SAE 1=Manufacturer Fault designator 1=Fuel and air metering 2=Fuel and air metering (fuel system) 3=Ignition system or misfire 4=Auxiliary emissions control 5=Vehicle speed, idle control, and auxiliary inputs 6=Computer and auxiliary output 7=Transmission 8=Transmission 9 and 0=Category to be determined Figure 14-10. Typical OBD II trouble code. This particular code indicates a low input signal to the transmission fluid temperature sensor. There are 8,000 possible OBD II codes. While all this capacity is not presently being used, a modern vehicle ECM may be programmed with several hundred trouble codes. Figure 14-11 is a list of some current OBD II transmission trouble codes. Other Scan Tool Functions In addition to retrieving trouble codes, the scan tool can be used to retrieve other information from the vehicle computer. This information may include speeds at which shifts occur, converter clutch application speed, current gear, and transmission/transaxle temperatures and pressures. Some scan tools also display the desired gear for the particu- lar engine and vehicle speed. This allows the technician to instantly determine whether the transmission is in the proper gear. Other scan tool readings give input and output shaft rpm, which can be used by the technician to diagnose slip- page in a particular gear. Figure 14-12 shows transmission- related data that can be obtained using a scan tool. Other conditions that can be monitored by the scan tool include engine RPM and temperature, sensor inputs, vehicle speed, and outside air temperature. In OBD II systems, scan tools can also tell the technician whether or not there is an engine miss, and if so, which cylinder is causing the problem. Some scan tools can interface with the ECM to provide snapshots, or freeze frames, of engine and transmission operation. The snapshot is a scan tool feature that records vehicle operating conditions immediately before and after a malfunction occurs. This information helps the technician determine exactly what happened to cause the problem. To record the snapshot information, the technician must drive the vehicle with the scan tool attached until the malfunction occurs. The technician can then access the readings through the scan tool. Some vehicle ECMs save snapshot information when a malfunction occurs during normal operation. The technician can retrieve this information using the scan tool. Scan tools can also be used to test output solenoids by bypassing the ECM and commanding the solenoids to operate. One of the most useful ways a scan tool can be used is during a road test. Attach the scan tool to the vehicle’s diagnostic connector and observe readings as you drive the vehicle. Information on shift speeds, shift qual- ity, slippage, and other data can be observed under actual driving conditions. The scan tool can be connected and then placed on the dashboard or seat for road testing. The safest method of performing a road test while using a scan tool is to have someone else drive while you check the scan tool readings. Always use lightly traveled roads during the road test, and be alert for other drivers, traffic signals, and road conditions. The scan tool will display readings similar to those shown in Figure 14-13. These readings can be compared with actual transmission or transaxle operation as the malfunction occurs. This helps determine whether the problem is in the computer control system or another system. Actual scan tool displays vary widely. Scan tool instructions should be followed exactly to ensure that you obtain the proper readings. Checking System and Component Operation Once you have isolated the problem using the scan tool, you can proceed to test individual systems and components as outlined in the following sections.