'97 MB C230: CEL, code P1747

[Benzadmiral]

For the last couple of weeks my 5-speed, electronic 722.6 autobox has been acting funny on occasion. I'd brake sharply, and then if I tried to accelerate immediately, the transmission would seem as though it were not engaging. I'd give it gas, and then it would shift properly. This didn't happen if I braked sharply and then waited a second to accelerate.

Yesterday, as I sprang onto the Greater New Orleans Bridge at rush hour, I braked sharply . . . and felt a jerk, and my Check Engine Light came on!

The car seemed to drive normally, though. I went to Autozone, and their scanner came up with P1747, "Pressure Control Solenoid 'A' short circuit." The CEL was out when I restarted the car after this, and didn't come on during the 3-mile drive home. Again, the car did fine on the 9-mile trip in to work this morning.

My regular Merc independent isn't too worried, since the CEL and symptoms haven't returned. I'll have him do a fluid and filter change next week. It's been about 4.5 years and 35K miles since it was done at the dealer for the previous owner. The fluid level is hard to read, since they don't give you a dipstick (!), and the fluid needs to be at a specific temperature to get a true reading.

Has anybody ever run across this code before? Are we talking about major transmission work?

TIA,

 

[unDummy]

Either the solenoid is failing or the wiring to it has a short circuit.
There are also mechanical failures that can cause error codes like this even when there is no issue with the wiring or solenoid.
Inspect the 'Solenoid Pressure Regulator Valve Spring'.
Test all the electricals/solenoids or just replace them all.

I would definitely worry!

If the filter/fluid change reduces or eliminates the issue, consider more frequent maintenance. Besides a pan drop, you would need to fully flush the transmission to remove all the old spent sheared ATF, or minimally drain the TC too if it has a drainplug.

If you're lucky, thin ATF could be causing the problem.

 

[The Critic]

If it's the "LINE & SHIFT PRESSURE SOLENOID," then it runs $194.27 plus shipping. There are two of these in the transmission. Depending on the labor needed to reach the solenoids, this entire job may run around $1000 with parts and labor.

 

[Benzadmiral]

Update: I had the fluid and filter changed yesterday. My mechanic said there were definitely no metal shavings in there, and it looked good, except that the filter (which he suspected hadn't ever been changed!) was pretty gunked up. I suppose that could have kept the fluid from getting to all the internals, right? The 722.6 transmission is pretty finicky about fluid level, I understand.

The car behaved impeccably last night (10 miles, about half city traffic) and this morning (9 miles, about the same).

Maybe I got lucky this time. I'll certainly have it done every three years in the future.