SECOND TRANSMISSION ISSUE
December 27, 2009
by: jovial_cynic
by: jovial_cynic
I recently started having issues with the Dodge Caravan transmission again. Previously, the problem was traced down to a bad speed sensor; the symptoms included an erratic speedometer and cruise-control that kept hunting for the right speed. (That's an output speed sensor issue, by the way).
This time around, the check-engine light came on, and while driving on the freeway, the transmission went into neutral (free-revving). I pulled the van over, turned the car off, and then turned it back on again to see what would happen. If the van was going to remain stuck in neutral, I knew I was going to need a tow truck to come get me. Fortunately, the Dodge transmissions are able to go into "limp-mode," which basically puts the transmission into second gear and leaves it there while you're driving it. This makes for rather high-RPM free-way driving, but at least you can get it home so you can work on it.
Anyhow, I got the van home and picked up another set of speed sensors (still under warranty through Schucks Auto (Kragen Auto, locally), hoping that the issue was the input speed sensor. That, and it's always best to start with the least expensive repairs first, or you may end up spending lots of money on parts you don't actually need. Free is rather cheap, which is why I started with them.
After swapping out the sensors, the van was still in limp-mode, so the next thing I wanted to rule out was a possible wiring fault between the sensor and the transmission computer.
Not wanting to spend a lot of time trying to trace down shorts in the wiring, I figured the easiest way to check for faults was to run back to Kragen and borrow their diagnostic scan tool. They keep an Innova scan tool for rentals, and that seems to be a pretty good product.
The sensor reported two codes: 755 ("Shifter Solenoid B") and 700 ("General Transmission Fault"). This was good and bad news. The good news was that the problem was unrelated to the speed sensors, so I probably wouldn't have to try to trace down a shorted or disconnected wire somewhere. The bad news was that I had no idea what "Shifter Solenoid B" was, so I had to do some research.
A couple of quick google searches pointed to the following diagram:
The shaded section is the solenoid pack.
Wanting to rule out a connection problem (as opposed to a faulty device), I popped off the 8mm that held down the gray plug cap.
The plug was covered in oil - transmission fluid. There's no good reason for transmission fluid to get onto this connector.
The terminal was also wet. Somehow, an internal leak on the solenoid pack was forcing oil into the connector, which meant I'd have to replace the pack.
Here's the bad solenoid pack. Because the fault is internal, you can't tell that there's something wrong with it by looking at it.
NOTE: Dirt builds up behind the solenoid pack on the transmission. Try to clean that off before removing this part, or the dirt will loosen up and fall under the solenoid pack while you're removing it, and you'll end up with dirt in the oil passages on the transmission. I spent a lot of time with Q-tips extracting dirt. Not fun.
I checked on the local auto store websites, and found that Auto Zone could order the part for $179 with a 3-month warranty. I didn't want to wait for a special order, so I called up the Dodge dealership, who carried the part for $240. After talking with the Dodge guy a bit, I learned that this particular part was on its third version, due to known defects and leaks. Not knowing if Auto Zone or the other sites carried the latest version, I decided to go with the Dodge part.
Three bolts later, the new solenoid pack was installed. I ran the scan tool on the van again, and the 0755 code was gone. I still had to clear the 0700 codes, which apparently don't go away by themselves, and three days later, the check engine light has not come back on, and the transmission is changing gears just fine.
NOTE: In the event that your Dodge is stuck in neutral, I believe that you can force it into limp-mode by removing the plug to the shift-solenoid pack, which is bolted down with an 8mm bolt.
This time around, the check-engine light came on, and while driving on the freeway, the transmission went into neutral (free-revving). I pulled the van over, turned the car off, and then turned it back on again to see what would happen. If the van was going to remain stuck in neutral, I knew I was going to need a tow truck to come get me. Fortunately, the Dodge transmissions are able to go into "limp-mode," which basically puts the transmission into second gear and leaves it there while you're driving it. This makes for rather high-RPM free-way driving, but at least you can get it home so you can work on it.
Anyhow, I got the van home and picked up another set of speed sensors (still under warranty through Schucks Auto (Kragen Auto, locally), hoping that the issue was the input speed sensor. That, and it's always best to start with the least expensive repairs first, or you may end up spending lots of money on parts you don't actually need. Free is rather cheap, which is why I started with them.
After swapping out the sensors, the van was still in limp-mode, so the next thing I wanted to rule out was a possible wiring fault between the sensor and the transmission computer.
Not wanting to spend a lot of time trying to trace down shorts in the wiring, I figured the easiest way to check for faults was to run back to Kragen and borrow their diagnostic scan tool. They keep an Innova scan tool for rentals, and that seems to be a pretty good product.
The sensor reported two codes: 755 ("Shifter Solenoid B") and 700 ("General Transmission Fault"). This was good and bad news. The good news was that the problem was unrelated to the speed sensors, so I probably wouldn't have to try to trace down a shorted or disconnected wire somewhere. The bad news was that I had no idea what "Shifter Solenoid B" was, so I had to do some research.
A couple of quick google searches pointed to the following diagram:
The shaded section is the solenoid pack.
Wanting to rule out a connection problem (as opposed to a faulty device), I popped off the 8mm that held down the gray plug cap.
The plug was covered in oil - transmission fluid. There's no good reason for transmission fluid to get onto this connector.
The terminal was also wet. Somehow, an internal leak on the solenoid pack was forcing oil into the connector, which meant I'd have to replace the pack.
Here's the bad solenoid pack. Because the fault is internal, you can't tell that there's something wrong with it by looking at it.
NOTE: Dirt builds up behind the solenoid pack on the transmission. Try to clean that off before removing this part, or the dirt will loosen up and fall under the solenoid pack while you're removing it, and you'll end up with dirt in the oil passages on the transmission. I spent a lot of time with Q-tips extracting dirt. Not fun.
I checked on the local auto store websites, and found that Auto Zone could order the part for $179 with a 3-month warranty. I didn't want to wait for a special order, so I called up the Dodge dealership, who carried the part for $240. After talking with the Dodge guy a bit, I learned that this particular part was on its third version, due to known defects and leaks. Not knowing if Auto Zone or the other sites carried the latest version, I decided to go with the Dodge part.
Three bolts later, the new solenoid pack was installed. I ran the scan tool on the van again, and the 0755 code was gone. I still had to clear the 0700 codes, which apparently don't go away by themselves, and three days later, the check engine light has not come back on, and the transmission is changing gears just fine.
NOTE: In the event that your Dodge is stuck in neutral, I believe that you can force it into limp-mode by removing the plug to the shift-solenoid pack, which is bolted down with an 8mm bolt.
