I have a 2001 S40 Volvo. Recently, the check engine light came on as well as the flashing arrow indicator which means a transmission malfunction. Using an OBDII reader, I found the codes P0700 and P0798. P0700 is a "transmission control error" and P0798 is a "pressure control solenoid C electrical" error. Does anyone know what is required to fix this problem? Is the pressure control solenoid part of the electronic control module and I have to replace the whole module, or is the pressure solenoid separate and can be replaced separately? And where is it located?

 

Sounds like it might be one of the S soleniods.
Did you clear them and how fast do they come back?

 

No, I didn't try to clear them. I wanted to keep them there if I had to take the car to the shop. I did download the online manual to the car. It said that there is a Transmission Control Module in addition to the Electronic Control Module, and it has separate diagnostic codes. The ECM codes won't clear unless you clear the TCM codes first. I only have a simple OBDII reader, and I don't think it'll work on the TCM.

I figure it has to be either the solenoid or TCM module. Do you know which one has a history of greater failures in this car?

 

Soleniods by far.

 

Well, I took the car into the Volvo dealership. They said it was the SLS solenoid which controls the line pressure in the transmission. The error code was TCM-0114 which is:

"Line pressure solenoid SLS regulates the line pressure in the transmission. The solenoid is controlled by a power stage in the transmission control module (TCM) output. The transmission control module (TCM) uses the power stage to control the current to the solenoid. A low amperage results in a high line pressure. A high amperage (approximately 1 A ) gives a low line pressure. The amperage is primarily affected by the throttle position. Diagnostic trouble code (DTC) TCM-114 is stored if the control module registers that there is an open-circuit in the circuit for solenoid SLS. Solenoid SLS cannot then control the line pressure."

They wanted $1600 to fix it. They said they can't replace the SLS solenoid by itself since Volvo only sells the module that contains all of the solonoids, and that costs $960. Then add 6 hours of labor. They also said they couldn't measure the resistance across the solenoid for whatever reason - which is what the manual recommends.

Looking at the description of the error code, it says that it is generated when there is an open-circuit in the circuit for the SLS solenoid. Being as the car is now functioning properly, it appears that the problem is intermittent and not a "definitely this is broken" problem. I would think that if the solenoid was bad, it would have a continuous open, not intermittent. This leads me to think that the problem is a bad connection in the harness or connector part of interface. So I told them to clean things up and wait and see if it happens again.

Any thoughts?

 

I will have to double check on the parts issue. And see what I find out about that.

But I would drive it and see if it comes up again.

 

It sounds to me that they are speaking of the linear solenoids in the valve body. These are only a couple hundred dollars or you can get a completely rebuilt valve body and put it on yourself. I just replaced all of the solenoids in my 2001 S40 and it wasn't a big deal. Look for the YouTube videos on the subject!