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Hesitation, Jumping - Transmission Problem?

Auto Trans cutaway photo

Transmission hesitation, or at least what sounds like automatic transmission hesitation, is a relatively common issue with older vehicles. As vehicles age, things inevitably begin going wrong. But hesitation can be several things.

The first thing to do is to rule out the easy stuff. Answering the following questions can help the process of narrowing down the issue:

  • Is the car hesitating only at lower speeds? Higher speeds?
  • Is it idling OK? Rough?
  • Is the hesitation happening only at certain times of day (first thing in the morning)? Or only when the car is cold (not run in a while) or hot (has been running)?
  • Is the transmission fluid level OK and is the fluid clean?

That last question is something that should be addressed regardless of whether it fixes the hesitation problem. Transmission fluid needs to be at the right level and the fluid itself needs to be clean. All the time. Any change to that can mean problems. Low fluid levels or dirty fluid are usually indicative of something else being wrong as well.

If the car hesitates only at lower speeds, then the problem is more likely to be fuel or air intake (an idling issue) than it is a transmission problem. Change out the fuel filter, check the ECU for codes, and run a test (if possible) on the mass airflow sensor and/or first bank oxygen sensor. These could be the problem, causing the engine to not rev high enough to shift gears properly.

At higher speeds, hesitation is more likely to be caused by the fuel system not delivering enough fuel. Do a fuel pressure test (read about that here). You should also plug into the car and pull codes to see if there is anything listed. Another culprit could be the speed sensor, which will usually throw a code if there is something wrong.

If the hesitation only happens at certain times, such as first thing in the morning, when it's been frosty or had a heavy dew outside, or only when the car is cold (before it's properly warmed up) then the issue could be in the air intake, MAF sensor, or fuel system. Moisture getting into the system can cause a lot of problems. You'll need to look for pinhole leaks or indications of moisture getting into the fuel or air intake.

If the hesitation only happens when the car is at operating temperature, the issue could be an overheat issue with a component or in the fuel rail. When the engine is hot and the hesitation issue begins, park the car and quickly do temperature readings (using an infrared thermometer or temperature gauge gun) on the fuel rail, evaporator, etc. If the fuel system is vaporizing before injection, the problem will likely mean that an engine code for misfires or similar issues will be thrown, so pull those codes and see.

The last thing to check before diving into potential transmission problems is the vacuum system. On older vehicles where the engine vacuum determines things like shifting and so forth, a leak could mean that the transmission shifts incorrectly or not at all.

On modern cars, the engine and transmission will likely have separate computers. Be sure to pull codes from both sources or have a mechanic do so for you. A very likely problem is transmission fluid viscosity or the TCC solenoid.

Hopefully this short guide helps find some of the problems possible in transmission hesitation. There are others, but these are the easiest to look for and the most likely problems.