I know that the internet has already told you a lot about the “Transmission Over Temp” error message in a Grand Cherokee, but everything I read about it was so far away from the true reasons for the problem that I decided to write my own article and tell you how to fix this issue and what it may mean for your Grand Cherokee.
First of all, this problem most often occurs on older Grand Cherokee SUVs – the second and the third generations (1999-2010). In newer vehicles, Jeep addressed this problem and made the cooling system for the tranny better as well as the tranny design changed dramatically and the sensors became much more durable.
In short, your Jeep Grand Cherokee may show the “Transmission Over Temp” error message because of a bad temp sensor in the tranny, a clogged cooling system, a dying ECU, or actual overheating because of your driving style and road conditions.
In this article, I will look into each of these reasons and will tell you what exactly you should do to find and solve the actual issue.
What transmissions are affected?
This warning message may pop up in the Grand Cherokee with any transmission, but the 5-speed automatic version seems to be more prone to the issue. The 545RFE and also the W5A580 trannies are both affected.
They have a cooling system that helps them stay under high temperatures during off-road rides. When you are crawling in your Grand Cherokee uphill, it’s quite natural that the tranny will heat up a little more than usual. Also, when you tow something heavy, the transmission will be under a huge load.
Also, these trannies, just like the 4-speed automatic, have temperature sensors that will trigger the error message we are talking about today if they register high temperatures.
Why is the “Transmission Over Temp” message triggered?
If your Jeep Grand Cherokee shows this message, it may mean several things: your tranny is actually overheating and you need to do something with it, or there is a problem with one of the units that is in the chain of equipment measuring and processing data from your tranny.
I will list the major reasons for this issue and you will have an understanding of what may have happened with your SUV.
1. The tranny is actually overheating
The normal transmission temperature in your Jeep Grand Cherokee is anything under 220 degrees F (about 100 degrees C). This is considered high for most other cars, but those bulletproof torque-converter transmissions in the Grand Cherokee are actually OK to run at this temp when off-roading. Though on highways and in normal driving conditions, the temperature may go between 110 and 200 degrees F and it’s OK – you don’t need to repair anything if the temperature is like that in your Jeep.
When you are crawling uphill, towing a heavy trailer, driving off the road, or going at very high speed, it’s natural that your transmission is a little overheating. It still shouldn’t throw this “Transmission Over Temp” message if everything is OK, but in some critical cases, it may do that.
The first thing you should do is to stop your vehicle, let it cool down and see if the error message repeats.
2. The temperature sensor is dead or glitching
Your Grand Cherokee transmission is equipped with a temperature sensor and, as with any other sensor, it may malfunction and cause problems. One of the common reasons your Grand Cherokee is showing the “Transmission Over Temp” error message is the broken sensor.
Replacing this sensor is not an easy task. It’s located in the block of solenoids inside the transmission and you will need to take the tranny off the car and take it apart to get to the sensor. Of course, this is going to cost you some money for labor. The sensor itself is not really expensive.
You can check the work of the sensor with the help of professionals. Here’s how:
- plug the OBD2 scanner into the port in your Jeep and see the temperature that the transmission temperature sensor shows;
- use the dipstick tube to insert the thermometer into the tranny and see the actual temperature of the fluid in the tranny;
- compare those two readings and decide whether the sensor lying or not.
If the difference between those two readings is huge, the most likely reason for your problems is exactly the faulty transmission temperature sensor. If not, the tranny is actually overheating and you need to find the reason why.
3. The fluid level is low
It’s also possible that the automatic transmission is not lubricated and cooled properly. It’s cooled by the fluid, so the first thing to do is to check the fluid level with a dipstick or any other method you may use.
If the transmission fluid hasn’t been changed for more than 7 years or 60,000 miles, you better just change it now. The “Transmission Over Temp” message may also be triggered by the low-quality fluid that needs replacement.
4. The tranny cooling pipes are clogged
You may diagnose low or bad tranny fluid, change it, but then realize that the problem hasn’t gone. Now, you should also check the pipes of the cooling system – the ones that connect the transmission to the radiator. They are pretty thin and may get clogged if the fluid is contaminated.
In this case, the radiator will not be able to do its job and the transmission will be overheating. Of course, the Grand Cherokee will happily announce this every time it registers the high temperature in the tranny.
5. The dying ECU
One of the possible but very obvious issues of this error message randomly popping up in the Grand Cherokee is the glitchy ECU. If your Jeep has over 200,000 miles on it or if it was engaged in flood damage, or if the ECU was in contact with water in some other situation, chances are that the ECU is going to die soon.
Before its death, it has some kind of glitches and very often these glitches come to life as the “Transmission Over Temp” error message in the dash of your Jeep. Unfortunately, checking this is very hard. But if this message just randomly appears and then goes away to not show up a day or two, you may suppose it’s about the ECU problems.
Can you keep driving when you see the “Transmission Over Temp”?
While in some cases driving your Grand Cherokee further after you see this message won’t cause any harm, in other circumstances, it can kill the transmission. Unfortunately, you can’t understand this immediately on the roadside, so you will have to stop and let the transmission cool down.
If you see the “Transmission Over Temp” message on the dash of your Grand Cherokee, do the following:
- find a safe place to stop without breaking the road rules;
- stop the vehicle and turn off the engine;
- wait for at least 20 minutes;
- you may want to open the hood to let the units cool down faster;
- start your engine and make sure there is no high-temp message anymore;
- keep driving but pay attention to the possible repeat of the problem.
After you see this message, plan your visit to the repair shop. Ask your mechanic to measure the actual temperature of the tranny fluid and check the readings of the sensor in the transmission with the OBD2 scanner. This way, you will get more information about what’s happening with the vehicle.
What are the consequences of actual transmission overheating in the Grand Cherokee?
Your good old Jeep doesn’t like overheating. While the engine has some systems that help it cool down intensively like different fan speeds and thermostats, the tranny has only very primitive cooling pipes and (maybe) a tiny radiator that wasn’t installed in all versions of the Grand Cherokee.
So, if your transmission is overheating, it will suffer immediately. First of all, the properties of the fluid will change and it will stop lubricating the moving parts of the transmission. Also, the heat will affect the shape of the parts and the transmission will start working harshly and destroying itself on the go.
The high temperature will cause the slipping of the tranny. But if you experience this, your transmission is already asking for some repairs.
Overall, the overheating transmission in your Jeep Grand Cherokee is not a good thing and you should avoid it at all costs.
Can you prevent your tranny from overheating?
You may find some ideas on how to install an additional radiator and improve the work of the transmission cooling system in the Grand Cherokee WJ and WK. But I think it’s only worth investing in these measures if your tranny actually overheats because of unusually tough off-roading or towing something extremely heavy.
In all other cases, the “Transmission Over Temp” message will only mean that something is wrong with the temp sensor in the tranny or the ECU, or the level of fluid in your transmission is too low. So, better check this first and only then start considering any improvements in the cooling system in your Jeep.
Also, remember that when you see this message in high mileage like 200,000 miles plus, it’s most likely telling you that the ECU is living the last months of its hard life.