Work Flow

INTRODUCTION
The A/T control unit receives a signal from the vehicle speed sensor, throttle position sensor or inhibitor switch and provides shift control or lock-up control via A/T unit solenoid valves.

The A/T control unit also communicates with the ECM by means of a signal sent from sensing elements used with the OBD related parts of the A/T system for malfunction diagnostic purposes. The A/T control unit is capable of diagnosing malfunctioning parts while the ECM can store malfunctions in its memory.

Input and output signals must always be correct and stable in the operation of the A/T system. The A/T system must be in good operating condition and be free of valve seizure, solenoid valve malfunction, etc.
It is much more difficult to diagnose a problem that occurs intermittently rather than continuously. Most intermittent problems are caused by poor electric connections or improper wiring. In this case, careful checking of suspected circuits may help prevent the replacement of good parts.

A visual check only may not find the cause of the problems. A road test with CONSULT (or GST) or a circuit tester connected should be performed. Follow the "Work Flow" charts.

Before undertaking actual checks, take a few minutes to talk with a customer who approaches with a driveability complaint. The customer can supply good information about such problems, especially intermittent ones. Find out what symptoms are present and under what conditions they occur. A "Diagnostic Worksheet" should be used.

Start your diagnosis by looking for conventional problems first. This will help troubleshoot driveability problems on an electronically controlled engine vehicle.





WORK FLOW
A good understanding of the malfunction conditions can make troubleshooting faster and more accurate. In general, each customer feels differently about a problem. It is important to fully understand the symptoms or conditions