How can you tell a transmission problem from an engine problem?

Summary:

Jaden acknowledges that separating a transmission problem from an engine problem varies case by case and can genuinely be difficult. He gives a concrete example of overlap: an engine misfire can feel very much like torque converter shudder, and those cases are hard to sort out at times. His primary diagnostic tool is a road test, and he states that most of the time he can tell which system is at fault by driving the vehicle. He then offers the general rule he applies. If the transmission is slipping, engine speed rises while power fails to reach the wheels. If the problem is in the engine, the vehicle also loses power, but engine speed bogs down instead of climbing. The direction the tachometer moves under load is the tell that separates the two.

Answer:

So that varies a lot. There's times when you have a misfire in the engine and it feels like torque converter shudder. Those are actually kind of hard to figure out at times. Most of the time I can tell by driving it. There's other times when, generally speaking, if it's a transmission problem, like the transmission's slipping, what'll happen is the RPMs are going to go up and it feels like you're not getting power to the wheels, like to the ground. If it's an engine problem, generally speaking, the RPMs are going to bog down and you're going to lose power. Like, power is not getting to the ground, but the RPMs go down, not up. So in both cases you're losing power to the ground, and that's why people confuse them. The difference is which way the RPMs move while it's happening. Up means the transmission is slipping. Down means the engine is the one struggling.