Work Flow: Introduction

The TCM receives a signal from the output speed sensor, accelerator pedal position sensor (throttle position sensor) or transmission range switch. Then provides shift control or lock-up control via A/T solenoid valves.

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.

Fig 1: TCM Communication Chart

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It is much more difficult to diagnose an error that occurs intermittently rather than continuously. Most intermittent errors 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 may not find the cause of the errors. A road test with CONSULT or a circuit tester connected should be performed. Follow the "DETAILED FLOW".

Fig 2: Diagnosing Intermittent Errors

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Before undertaking actual checks, take a few minutes to talk with the customer who has the driveability complaint. The customer can supply good information about such errors, especially intermittent ones. Find out what symptoms are present and under what conditions they occur. A "Diagnostic work sheet" as shown in the example (Refer to DIAGNOSTIC WORK SHEET ) should be used.

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

Also check related Service bulletins.

Fig 3: Starting Diagnosis By Looking For Conventional Errors First

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