Shop Foreman Brent handed me my next work order - Check Transmission on a 2005 Chevrolet Malibu Maxx. “The driver said something about the transmission slipping,” was Brent's comment to me. No other specifics were available, which is common. “See what you can find.”

The first step in ANY repair process is to verify the concern. A thorough road test is absolutely essential, especially in cases like this. Thankfully, I had a “check engine” light on, which I was hoping would be able to provide some direction. My next clue appeared after the first 10 feet of forward motion.

This particular Malibu Maxx is powered by Chevrolet’s 3.5L V-6 paired with GM’s 4T45-E 4-speed automatic transmission. Backing out of the parking space and shifting into drive, I immediately discovered that I had no 1st gear, (it started out in 2nd gear). Out on the road, I realized that I also have no 4th gear. The 2nd gear – 3rd gear shift was fine. Back at the shop, I hooked up our scan tool to retrieve codes. One single code appeared - P0751, which is defined as “1-2 Shift Solenoid stuck.” My automatic transmission knowledge is extremely limited. However, it appears the code I am seeing and the symptom I verified could be directly related. If a shift solenoid is not working, it is possible that a gear or gears could not be available.

The modern EEC V Powertrain Control Module allows for something called “Active Command” during diagnostic testing. Basically, using a scan tool, I can tell the computer to do something, and see if a) the command is being received, b) the command is being executed, and c) sensors designed to monitor such commands are doing so. My shop's Snap-On Verus scanner utilizes this feature through its “Functional Tests” menu. My goal was to command the transmission to shift and see if it happens.

On the road with me behind the wheel, night foreman Larry started punching buttons on the scanner. We could get the car to shift from 2nd gear to 3rd gear and back again via scanner commands. However, even though the command to shift into 1st gear was being received, the transmission was unable to physically do it. Once again, logically, my limited-knowledge self sees a correlation. I have no 1st gear. The code I have is for a stuck shift solenoid. And now I see that the module is receiving a command to shift, but can’t do it.

Larry makes a call to the dealer to check on shift solenoid prices and availability. Not only does the parts department report, “we’ve seen problems with them,” replacement solenoids are kept on the shelf, which adds reinforcement to the “we’ve seen problems with them” statement. One half-hour later, Larry had two of them in his hands. He got two because a) the 1-2 and 2-3 solenoids are the same, b) Athens Chevrolet had two in stock, and c) since I’m replacing one, it would be foolish not to replace the other while I was in the neighborhood.

Shift solenoids are located on the transmission valve body. In rear wheel drive applications, the valve body is mounted horizontally above the transmission filter inside the pan. On this particular front wheel drive application, the valve body is mounted vertically behind the transmission side cover. Think of the side cover as another large transmission pan, but mounted on the side of the unit. In other words, they’re somewhere under the mess of parts seen in the photo above.

I had never done anything like this before. So I didn’t have any points of reference for advice on where to begin. I know that being able to see what you’re working with is always a good thing. Items such as the battery, battery tray, wiring harness, and any other close components needed to be removed, or at least moved aside to access the top of the transmission. I decided to start there first as seen in the photo above.

Next, I removed the battery tray mounting bracket which gave me a decent amount of access from the top of the vehicle.

I also removed the shift linkage and transmission range sensor so I could get to the remaining side cover bolts. Access is actually quite generous all things considered.

With the transmission side cover sitting next to the driver's side front wheel, I needed to make some access in that area. A couple of things can be seen from the vantage point in the photos above and below.

The transmission mount is bolted directly to the side cover. And the left front half-shaft passes right through the side cover. Both had to be removed.

As long as I had the car in the air, I removed the lower transmission pan first to start the transmission fluid draining process.

The draining process actually took quite a bit longer than expected. Dropping the pan means draining approximately 4 quarts of fluid from unit. Draining the bulk of the fluid is easy. It’s eliminating the dribbles and drops that will Chinese-Water-Torture-you to death that takes a while.

I discovered some good news at this point. I didn’t find anything unusual in the transmission pan or filter. Finding parts in the transmission pan would have immediately changed the direction of this repair, and cost the department in question much, much more. At this stage, I also removed the transmission filter, which I will be replacing.

I know I will be removing the transmission mount on the driver’s side of the car. This means the engine/transmission assembly will need to be supported from above. This is done through the use of an engine support seen in the photos above and below.

The idea is pretty straight forward. I wasn't removing the engine or transmission. All I needed to do was keep the left side of the assembly in the air. Hooking a chain and threaded eyelet to the engine support took care of this concern.

Next, I removed the left front half-shaft. Loosening the lower ball joint pinch bolt allows the lower control arm to be separated from the wheel knuckle. After removing the axle nut, the strut and knuckle can then be slid aside so the drive axle can be removed. Since I’m not removing the strut, I always wrap a rag around the lower ball joint to protect the dust boot from getting torn.

With everything out of the way, I now had a decent amount of access to the transmission side cover.

The side cover is held in place by 12 bolts. With those bolts removed, I could now slide the side cover out of the way just enough to access the shift solenoids on top of the valve body.

Thankfully, I had enough room to tilt and twist the side cover so I could access the solenoids. If that would not have been the case, or if I had to actually remove the side cover completely, I would have had to play with the front subframe, (i.e. removing a bunch of subframe bolts and tilting the entire engine/transmission assembly downward on the left side of the car). This is because with everything in place, there is not enough room between the transmission and the body of the car to accommodate side cover removal, (it’s too wide).

The two shift solenoids are located at the top of the valve body and face rearward. I have them highlighted in the photo above.

Each solenoid is held in place by a u-shaped clip.

I unhooked the wiring harness connectors, released the clips, and removed the solenoids.

As I was removing the 1-2 Shift Solenoid, I heard something fall.

The object in question turned out to be a plastic cap on the solenoid that had broken loose. When I removed the solenoid and found the cap, I made a discovery.

The broken cap had caused the plunger inside the solenoid to seize. Therefore, when the computer commanded the solenoid to open and close, it was unable to do so, which produced the P0751 stuck solenoid code. Comparing the old part to the new one, it became obvious that the solenoid was physically broken.

Making a discovery like that is a wonderful experience. Not only does it reinforce a diagnosis that I wasn’t 100 percent sure of in the first place, it is also a great confidence builder. I was able to reason my way through a problem I was not familiar with. And it felt quite good doing so.

With the solenoids out of the valve body, I made sure the valves controlled by the solenoids were free and functional, which they were. Installing the two new solenoids was a simple matter of lubricating the o-rings with transmission fluid, positioning each in place, installing the retaining clips, and reattaching the wiring harness connectors.

With the new parts installed, the car went back together. Larry and I prepared to road test the car with fingers crossed. Shifting into drive resulted in 1st gear. At the back of our parking lot, 2nd gear arrived. Once out on the road, all 3rd and 4th gears made themselves known. Shifts were smooth at light throttle application and firm when they needed to be, (like accelerating to get on the highway). Above 45 mph, the torque converter locked up like it is supposed to do. Back at the shop, a check under the car revealed no leaks of any kind. Larry drove the car once again later in the evening just to ensure that everything was working, which it was. The check engine light stayed off, like it should. As scary as the unknown can be, conquering it can be a very rewarding experience.