Technically Speaking
- Author: Wayne Colonna, Technical Editor
It is not uncommon to hear of a technician investigating the inside of a computer as part of a diagnostic routine, especially when dealing with odd continual electrical problems.
Sometimes when the box is opened, a distinct burnt odor confirms the technician’s hunch that it was fried “Fred” causing the problem all along. Sometimes a cracked circuit board is the cause of those pesky intermittent trouble codes. On other occasions the box is filled with water from a leaking sunroof (Honda/Acura) or a leaking heater core (Mitsubishi/Hyundai), or it just had the misfortune of being in a flood.
In 1992-95 Toyota Camrys with the 540E transaxle, a leaking capacitor corroding the TCM circuit board has proved to be a notable and consistent failure. It frequently reveals itself by producing solenoid codes with no upshifts when the transaxle is hot.
Figure 1 shows the TCM split open. A red circle identifies the area of the problem capacitor. Figures 2 and 3 are closer views. You can see the dark-brown electrolyte that leaked out below the capacitor and onto the circuit board.
Scotty West, of Auto Computer Exchange in Davie, Fla., said this leak sometimes is hard to detect, as it may begin with a clear-color leak before the dark brown is visible. Other times the leak will show up as white and green, especially if it has had some time to deteriorate the circuit board.
In instances in which this failure has been discovered before the circuit board has deteriorated, it’s possible to replace only the capacitor. This process requires the proper soldering equipment and the ability to accomplish this task successfully.
1990-1991 Lexus ES250 and ’92-93 ES300 also are subject to this failure.
In the LS400 and the SC300 equipped with the 340E rear-wheel-drive transmission, a different type of problem occurs when a similar capacitor in the computer leaks. One of the injectors fades in and out, and a cooling fan turns off.
Many thanks to Ritchie and John of Al’s Transmissions for the tip and the photos, and to Scotty West, who provided additional details. I also thank ATSG technician Mike Souza for putting this on my desk to write about it.
