Diagnosis Archives - Transmission Digest
Understand Systems Involved in Diagnosis

A while back we had a customer come into our shop stating, “The vehicle sometimes has a VSC (Vehicle Stability Control) error and won’t go past fourth gear, but today it seems fine.” The vehicle was a 2007 Lexus LS460 with 132,561 miles, and equipped with an AA80E 8-speed transmission and a 4.6L engine. As with routine diagnosis, I started with a road test, a scan of all modules, and an undercar inspection.

Sometimes It’s Not So Bad When It’s Bad

The input-shaft and output-shaft speed sensors used in the AF23/33-5 (AW55-50SN) are two-wire Hall-effect sensors, which means they are supplied with a voltage source on one wire and send a signal back to the computer on the remaining wire.

The Great Unknown

Replacing parts is the last step in the repair process. The first step should be a methodical diagnosis to isolate the cause of the malfunction. This is not possible unless you understand how the component you are working on is supposed to operate and how it is related to the other systems that make up the modern motor vehicle.

Tips and Techniques for Standard-Transmission Diagnosis, Part 2

When you arrive at a formula that fits your operation, it must become what the Army used to call SOP (standard operating procedure) for handling technical problems, comebacks, never-lefts, initial diagnosis and root-cause failure analysis. Throw away the shotgun approach, stop making assumptions and follow the methodical process that you design to lead you to consistent problem solving. Let’s look at some real-world scenarios.