Shift Pointers
- Author: Pete Luban
With the introduction of OBD-II, a ton of additional codes became available (remember, we were always asking for more information). In some instances, these new codes were a great help because they did not just indicate a short or an open circuit but also pointed to parameters that were out of range, which included both mechanical and electrical problems.
And then sometimes, they were no help at all, just confusing and, in some instances, totally misleading!
Here’s the problem: OBD-II codes can be either generic (usually displayed as a “P0” code) or manufacturer specific (usually displayed as a “P1” code).
That being said, this article pertains to torque-converter-clutch (TCC) codes that are in the P0700 generic group; for example, P0740, P0742 and P0743. OBD-II generic codes supposedly are required to mean the same thing no matter which company made the vehicle.
However, it doesn’t mean that it has to be the exact same code, only that it must refer to the same general symptom. For example, the code for a mechanical TCC slip is P0742 for a GM vehicle, but it’s P0770 for a Lexus. Whether this complies with the OBD-II mandate doesn’t matter; this is just the way it is. Heck, some of the European auto manufacturers don’t even make these codes available, or they made them available for a model year or two and then they were gone.
When you look at the charts in figures 1-5, you will notice that code P0740 for a 1996 GM car equipped with a 4T60-E is mechanically generated, nut the same code for a 1997-98 GM truck is electrically generated. (This is within the same auto manufacturer!) Meanwhile, a 1997-98 Toyota uses P0770 for the mechanical fault and P0773 for the electrical fault, and a 1997-98 Nissan uses P0744 for the mechanical fault.
Also notice in figures 1-5 that some OBD-II codes were available in the 1994 model year. There were vehicles with OBD-II in the 1994 and 1995 model years because the manufacturer was “road-testing” the new diagnostic system to make certain it would function properly when OBD II became mandatory beginning with the 1996 model year.
As you can see, this becomes very confusing for a technician trying to interpret one of these codes properly – especially when Toyota, for example, defines code P0770 only as “Lock Up Solenoid.” Not very helpful, is it? Of course, what happens most of the time is that the lockup solenoid is replaced and the problem still exists.
When a mechanically generated code is stored, regardless of the code definition, it usually means that the computer has seen an incorrect engine- or vehicle-speed signal when TCC is commanded on or off.
In other words, a “Stuck Off” code results in TCC being commanded On, but the computer sees either TCC slip or too-high engine speed.
A “Stuck On” code means just the opposite: TCC is commanded Off, but the computer sees too-low engine speed. These scenarios are mechanically generated, not electrical!
Then there’s a bunch of codes for the TCC-solenoid electrical circuit that are also in the P0700 group. Also, there’s a rather large number of other electrical codes for the TCC solenoid, but they are manufacturer-specific, or “P1,” codes, which is another story.
I hope the charts contained in this article will help save some time and unnecessary parts costs. As for me, I’m gonna take a vacation after this one!
P.S.: Always use the generic part of your scan tool on the European vehicles; you never know – you might get lucky!
Pete Luban is a technical consultant for the Automatic Transmission Service Group (ATSG) and a frequent contributor to Transmission Digest.