Tales From the Bench - March - 2019

6F35: 5th Gear Starts and No Codes

As mechanics, we all like to fix cars and solve problems. When we get a car in the shop, that’s when we start our investigation. We get the customer’s complaints and start by checking the computer for codes. Then we investigate the codes and TSBs to find out where to look to fix the problem.

Most of the time we have a good idea of what’s going on and just need to verify the failed component and make the repair. But sometimes things don’t go as planned.

This one started with a call from longtime ATRA Member Andy Beon, owner of AB Transmissions in Yakima, Washington. He was working on a 2013 Ford Escape AWD 2.0L ECO-Boost with the 6F35 transmission.

They’d rebuilt the unit a few months back and the customer returned complaining of no power and the transmission not shifting correctly. So they began by checking the vehicle to confirm the customer’s complaint.

First they scanned for codes; there were no codes in any of the systems. They tried to drive it around the block but noticed right away that the transmission was taking off in the wrong gear.

They changed the valve body and solenoids to see if that resolved the problem. The solenoid numbers were put into the programming correctly, but it still had 5th gear starts and no codes.

That’s when they called the ATRA HotLine. I looked up bulletins and technical service information for clues. Nothing really stood out. So now we had to start diagnosing to find out what was working right and what wasn’t.

According to the scan tool, the computer was commanding 5th gear. When they first shifted into drive, the computer commanded 1st gear, then it switched right to 5th gear. But there were no codes.

First we tried a different scan tool to make sure the lack of codes wasn’t a compatibility problem. No luck: The computer was still commanding 5th gear starts and no codes.

Next, they grabbed a data capture of the range switch data (figure 1). The range switch read drive and the computer commanded 1st gear for a short time, then it switched to a 5th gear command while the range switch didn’t change.

But, while checking the range switch data, they found a clue: If they shift the unit into manual low, start driving, and then shift into overdrive, the transmission worked fine. They had all six gear upshifts and downshifts, no slips, and still no codes. But, if they came to a stop, it would go back to commanding a 5th gear start.

They performed a complete set of pressure tests and everything looked normal.

So why was the computer commanding 5th gear? It must have been trying to protect the driver or the car somehow. So we started looking at the wheel speed sensors and ABS system.

Some computer systems will put transmission in a higher gear and limit engine power when they see the wheel speed signal is off. But the wheel speed sensors and ABS system looked fine.

Next, we started checking the engine for clues. We looked at engine loads, fuel trims, misfires, temperatures, and knock sensor data. There wasn’t anything out of the ordinary. At this point, we knew the data had to be showing us the problem; we were just missing it.

That’s when we found it. The clue was in the first movie capture from the range switch data. When they moved the shifter to drive and the computer commanded 1st gear, the input speed sensor signal only dropped about 200 RPM (figure 2).

The computer noticed this and went into protection mode to protect the transmission by commanding 5th gear. The problem was that 1st gear engagement was too slow and the computer saw the slip.

They pulled the transmission and tore it down to inspect the 1-2-3- 4 clutch. The clutches looked good, but the lip on the piston was damaged (figure 3).

So they replaced the piston, put the transmission back together, and reinstalled it. Suddenly the computer was commanding 1st gear again and it worked perfect. They captured a new movie showing the confirmed repair (figure 4).

We’ve all run into that one car with a problem that makes no sense and won’t go away. This was a good reminder: step back and recheck your information and all the clues.

A few things were misleading on this vehicle: For one thing, if you shifted down manually to 1st gear, started driving, and then upshifted into overdrive, the car would work fine until the next time you came to a stop. In my mind, that ruled out the clutch pack, and the transmission was okay internally.

The second clue was that the pressure test seemed fine. It never occurred to anyone that we weren’t testing the 1-2-3-4 clutch. We should have checked pressure readings while driving.

As always, working together and gathering information is the best way to fix a difficult problem.