Evaluating Transmission Codes
This month, let’s dig deep on transmission codes. If you approach them right, you can save an enormous amount of diagnostic time and labor!
Let’s say you’ve got a shop that just installed a fairly modern solenoid-controlled transmission – anything from a 4L60E to a 10L80. If your customer is saying they’re seeing a dozen transmission codes, think for a minute about whether it’s actually possible for all of those solenoids/switches to fail at the same time. It’s not really, is it?
In this situation, I ask about what happened to the old transmission. If they say it had the same codes, that’s a pretty obvious red flag. Either they’re missing a wiring problem, it’s the wrong part, or there’s an ECM problem. Or maybe they just didn’t bother clearing the codes. It can be difficult to explain this to a retail installer or an old-school tech, but either you explain it – or end up crediting the part.
I handle these situations by getting back to basics: have them clear all the codes and see what comes back. Often those codes are from the old part, and if so, you’re good. But, if that doesn’t resolve it, ask them to unplug everything and look at the connectors on both sides. There is a great chance it’s going to have some bent pins, wasn’t plugged in all the way, or there is corrosion somewhere.
If all that checks out, ask them to reconnect everything and clear the codes to see what comes back. Start diagnosing from the lowest number code. It’s not always a harness – sometimes it is a shorted solenoid or an internal wiring problem. Most of the time it’s pretty simple.
Even though we’re talking about a fairly inexpensive part, it makes a big difference if you can spend an hour doing some diagnosing. If you do, you’ll probably be able to get the car back on the road same day, instead of spending 6 hours of labor, plus fluid, swapping it and wind up with the same problem again.
— Brandy Patton
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