Chances are you will not be rebuilding a transmission, but rather you will be listening to your customer’s complaint and diagnosing it. Knowing where to start is the most challenging part of the job.
The main focus of ASE’s A2 test is the electromechanical part of the transmission. The basic concept to remember is that if the electromechanical part of the transmission not correctly controlling the mechanical components of the transmission, a mechanical failure will happen.
Inspection
If you are dealing with a failed transmission or a malfunctioning transmission that is slipping or has harsh shifts, pull the pan and examine the fluid. Any large metal pieces or a large volume of smaller particles attached to the magnet is a sign that a clutch or brake has been damaged.
It is critical to look at the condition of the fluid inside the transmission.
Meter Skills
Some transmission can have more than 10 shift solenoids that can generate a lot of codes for opens and shorts. The shift solenoids also have monitors that track the performance with pressure sensors and speed sensors. Some of these codes will guide you to a problem with a solenoid or the circuit.
There are two strategies when diagnosing solenoids. The first is to look at the circuit with a meter. The meter can display an open or a short in the circuit by just looking at resistance. But, this is only half of the story. Using a scope to graph the inputs and the outputs will let you see more of the story.
Some manufacturers include in their service information contains “known good” waveforms that even give instructions on scope setup.
Transmission Replacement
If the transmission is replaced with a rebuilt or remanufactured unit, there are three items that need special attention.
First, clean all transmission cooler lines and make sure no contaminants are left behind. Second, when refilling the transmission, use the correct transmission fluid that matches the transmission specification.
Third, after the transmission replacement, reflash the latest software to the ECM. OEMs will improve software to optimize shift quality and transmission component longevity.
