4 SYMPTOMS OF A BAD TRANSMISSION CONTROL MODULE (TCM)
purpose
The purpose of the transmission control module (TCM) is to monitor sensors inside the transmission and communicate with the engine control module to be able to shift at the perfect time. The TCM also alerts the vehicle with diagnostic codes if something is wrong. The reason why a transmission control module can act up could be due to torn wires, a software issue, internal corrosion, cracks, or even a loose mounting bracket that creates unwanted vibrations.
If you have a manual transmission, don’t worry about it because your car doesn’t have a TCM.
location
The location of the transmission control module varies by car. It can be found behind the dashboard, under the air filter, on the transmission, next to the battery, or even behind the steering wheel. If you’re having trouble finding the TCM in your car, I recommend trying out this car repair manual.
Symptoms
engine light
The first symptom of a bad transmission control module is having the check engine light on. Some codes that might pop up are:
P0613
P0700
P0706
Ensure you can access your car's diagnostic codes by acquiring an OBD2 scanner here.
UNPREDICTABLE SHIFTING
The second symptom your car could have is unpredictable shifting. You’ll be driving down the road, increasing RPMs, and noticing your vehicle is either shifting too early or too late. It might also feel like a hard shift.
poor fuel economy
The third symptom of a bad TCM is poor fuel economy. In order for the engine to run its best, the transmission control module has to command the gears to shift at the perfect time. If the TCM is inconsistent with shifting gears, then it’s going to make the engine work harder than it needs to. And as a result, you’ll be spending more time at the gas station than usual.
shifting in neutral
The fourth symptom of a bad transmission control module is shifting in neutral while driving down the road. You might notice that your car can shift into neutral for no reason. For instance, the 2014 Jeep Cherokee had a huge problem with this.
limp mode
The fifth symptom your car could be experiencing is going into limp mode. Limp mode gets activated to protect you and your car. Your vehicle will be stuck in second or third gear along with limited speed.
The TCM should always be the last suspect when diagnosing, so make sure you’re checking other components that can cause similar symptoms first.
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