As technology advances, proper diagnostics have become more and more important. While most internal transmission problems are obvious, with burnt fluid or grinding noises. Some problems that seem like they are in the transmission can be outside. And for most technicians, including myself, when the diagnostic path leads towards a computer issue, we tend to get nervous about making that call, especially when some computers cost $2,500, and if it doesn’t fix the problem, it’s non-refundable. When this happens, it becomes an extremely costly mistake.
We recently had a 2013 Ford Edge with a 6F35 come into the shop bound up when the vehicle was running in forward and reverse. The customer stated they had not had any prior problems. They just got in it one morning, and the vehicle wouldn’t move. We found that it would roll with the vehicle off or in neutral. But in drive or reverse (with the engine on), it would bind up, with no codes set in any system. Our first thought was either a set of clutches had welded together, a valve stuck, or a solenoid stuck.
The inspection started with checking fluid level and condition. If it had a burnt odor to it, we probably would have assumed it was an internal problem and pulled the transmission without any further diagnostics at the time (This would have been a mistake). However, the fluid looked good and smelled fresh. We asked the customer if it had been flushed or serviced in the recent past. They stated it had not been serviced since they owned it.
We discussed the possible causes of this problem, including an internal drive train component, a stuck valve, blown gasket, a cross leak in the hydraulic circuits, a solenoid, or command to the solenoids. The easiest step was to find out if it were an external command issue. We could either disconnect the transmission connector or pull the fuse while running to see if it started pulling in either direction. We expected it to still have an issue since we assumed the problem was more than likely internal. But to our surprise, it started moving in both directions.
Our next step was to back probe some wires to check the solenoid commands. But first, we wanted to narrow it down to which solenoid wire to check. Looking at a solenoid application chart (Figure 1), we can scratch off the solenoids normally operating off the list. If SSA were stuck “ON,” we would have forward, with a bind in reverse. If the solenoid were stuck “OFF,” we would have reverse, but a slip going forward.
Shift solenoid E is used to switch shift solenoid D from operating the low reverse to the 4-5-6 clutches. If the low reverse clutches were stuck “ON,” we would still have forward and reverse, with a bind-up shifting to second. And if the 4-5-6 clutch were stuck “ON,” it would at least pull forward in fourth gear. The only thing that could cause a bind-up in both directions would be the 2-6 clutch.
When checking solenoid commands, one of my favorite tools in my box is my Snap-on Vantage Ultra. The Vantage (and the other upper-end Snap-on platforms) has multimeter capabilities and a built-in database. This saves me the time of digging through books or other software to find out which pin I need to check. In most cases, your connector pin identification charts are right there (Figure 2).
We attached our Vantage to the solenoid C command wire. According to the solenoid application chart (Figure 1), this solenoid should be “OFF” and showing battery voltage on the command side. But it was not, so we checked the voltage coming into the solenoid pack and the resistance through the solenoid. All this was ok. We then tried toggling the solenoid on and off with the scan tool. No change. This solenoid is being commanded on, and now we are leaning towards a dreaded potential computer problem.
But let’s not order that computer just yet; there’s more testing to do. The first step, check for potential wire harness damage, where another wire might be providing ground to that circuit. If this were the case, we’d expect it to set a code, but it is still worth looking into. Checking for wire harness damage can be very time-consuming, and hours are money. We would do a visual inspection for any obvious damage, then disconnect both ends of the wire harness at the transmission and the computer. Then begin checking continuity between that wire and ground, and that wire to all the other wires in the harness, at the computer connector.
We did the initial visual inspection, and everything looked good. We decided to bypass the wire from the computer to the solenoid pack by doing a continuity test on the wire harness. We could cut the wire at both ends and tie in a new wire temporarily, then check the voltages, but this would require resoldering the wire if it is not the problem. My personal preference is to purchase the terminals that go in the connectors (Figure 3) from either the dealership or online. Then use them, with a wire to bypass the wire in the harness. I save these jumper wires and label them for use on other vehicles, and have a nice collection going.
With the jumper wire in place, we rechecked the voltage, and it looks like the computer is providing ground to the solenoid. As we drew closer to condemning the computer, we wanted to do some more testing to make sure it was a computer issue. We checked the grounds coming out of the computer and found they were all showing about three millivolts, which was normal. The power coming into the computer was showing battery voltage, and the five-volt reference was correct.
At this point, we were convinced the computer was the problem, so we got one, installed it, and programmed it. And what a great relief it was when we put that Edge in gear, and it took off down the road. Even though we were sure it was the computer, it’s still always a little worrisome replacing something you can’t bench test like transmission parts (not to mention a happy customer that didn’t have to buy a transmission, and then the computer).
Back in the days of the seat of the pants diagnostics, those methods might have got that transmission on the bench when it did not need to be. Costing the customer a ton of money and possibly damaging a reputation. And without taking the time to do the diagnostics, that transmission might have been back on the bench a few times, looking for a problem that was not there.
