It’s easy to know the right thing to do after the problem’s fixed; it’s a little more difficult to track down the actual problem to begin with. Experience, time, and cost can sometimes lead to replacing parts that weren’t needed, wasting time, money, and reputation.
Anyone who’s been building for several years can tell you all about the old 125C and their lockup solenoid problems. They’d get warm, stick, and the converter clutch would stay on and kill the engine in forward and reverse.
Diagnosis was extremely easy: Disconnect the wire harness after the transmission was warm. If it still killed the engine, replace the solenoid. The solenoid was cheap, not too difficult to replace, and 99 times out of a hundred, it’d fix the problem.
Today we have the 62TE and the EMCC (Electronically Modulated Converter Clutch) solenoid. It’s cheap, not hard to replace, and a common problem. And, just like the 125C, the EMCC solenoid has feed oil all the time, which means it’s capable of lockup in 1st, killing the engine when put in gear.
We’ve seen this solenoid stick on, killing the engine when put in gear, and stick off, setting P0740 (TCC out of range). The problem has become so common that it’s tempting to replace the solenoid whenever there are torque converter clutch application issues with this transmission. To be honest, in some cases it’s easier and cheaper to replace the solenoid than to take the time to diagnose it.
In this case, we have a 2008 Chrysler Town and Country with a P0740 code. Initial scan data during the road test revealed zero slip on the torque converter clutch when it was cold. Then, after several miles of driving, the computer commanded lockup but the converter clutch didn’t apply.
Seeing the problem and knowing the solenoid is a common cause, the technician replaced the solenoid instead of diagnosing the system. But the converter clutch behaved the same way during the subsequent test drive: no torque converter clutch application after the transmission warmed up.
The source of the problem could be anywhere from the computer command to the converter clutch itself, and everything in between. That includes the command to solenoid, the solenoid (even though it was a new one), the converter clutch switch valve, the stator, the input shaft, the sensors watching the converter slip, or the converter itself.
Usually the best way to start diagnosing any converter clutch application issue is with a scan tool, watching sensors for problems and checking the solenoid commands. From there, it’s best to start at the middle and work toward the problem.
With any converter clutch application issue, the “middle” usually means checking cooler flow during converter clutch application. Once this vehicle was warm, there was no change in cooler flow when the computer commanded the EMCC to apply the converter clutch.
If the flow rate changed, it would confirm that the computer was commanding the solenoid the way it should, the solenoid was operating properly, and the valve stroked freely. That would leave us with a problem inside the transmission or torque converter.
In this case, there was no flow rate change, which meant there had to be a problem with the valve, the solenoid, or the computer command to the solenoid. Best place to start is outside the transmission. We might assume the command was okay because it showed up good on the scan tool. But we all know what assume says about you and me.
To check the signal from the computer, we backprobed terminal 3 in the C4 connector. When the vehicle was cold, everything looked good. But after several miles of driving, there was no signal change at the computer connector, even though the command looked good on the scan tool.
Next was to perform all basic checks: battery condition, and powers and grounds to the computer. We even performed a current draw test on the circuit. It was okay, so we were confident that the computer was the issue.
After installing the new computer and programming it, we reconnected a meter to the EMCC solenoid command wire and a scan tool to the data link connector (DLC). Then we took the vehicle for a test drive to verify the problem was fixed. Everything looked good, so we shipped the car and haven’t heard of any more problems with it.
There are times when replacing parts is easier and cheaper than performing the diagnosis. And when that part fails often, you might be even more inclined to take the easy road. But if you’re wrong, you’ll end up with an unhappy customer and higher costs than if you simply performed the diagnosis correctly.