Back on the Bench - December - 2021

In a Sticky Spot – An 09D Ratio Code Problem

A friend of mine recently called me about his daughter’s 2009 Volkswagen Touareg, with an 09D, giving him problems. They purchased the vehicle a few years ago, and it had been working great. His daughter said she started it one morning, it took off like normal. She drove it a short distance before it went to 3rd gear only and the check engine light came on. She had it towed to the shop for an inspection and to have it scanned for codes.

The vehicle had an OE code 17115, gear ratio error in 1st. He drove the vehicle through the lot, and it didn’t take much to set the code and go into failsafe mode, though he never felt it slip. He checked the transmission fluid; it was full and did not have an odor to it. He put it on the lift for a quick pan inspection, and it was clean. Most of his experience is with domestic vehicles, as well as Hondas and Toyotas. He usually doesn’t work on Volkswagens, but he had to get it back on the road as soon as possible since this is his daughter’s car.

We discussed the possible causes of a ratio code such as this. It could be anything from a speed sensor not reading correctly, a computer issue, a solenoid failure, a sticky valve, or even a leak in the circuit. My first recommendation was to run it on the lift to see if it still set the code, and while he had the scanner hooked up, check his speed sensors for any abnormalities. I also had him check the gear ratio PID, which should be 4.148. If the code did not reset, it was more than likely the K1 clutch slipping while on the road. If the code came back, I would be betting on a speed sensor or a computer issue.

He called back to tell me it did not reset the code on the lift, the speed sensors appeared to be ok, and the gear ratio was within specifications on the lift but did appear to be slightly off on the ground. With the speed sensors eliminated from the list of possible causes, our next step was to check the solenoid command, the solenoid itself, the valve body, and air check the circuit.

The N92 solenoid (Figure 1) controls the K1 clutches, and it is normally off while the K1 clutches are applied. The computer commands it on to shut off the K1 clutches in both 5th and 6th gears. There should be less than .1 amps on the wire in 1st through 4th, and close to 1 amp in 5th and 6th. He checked that, and it was within specifications. The next step was to drop the valve body to check the solenoid, valve body and air-check the K1 clutch circuit. However, he did not have a way to check the solenoid mechanical function, such as a hydraulic solenoid tester.

With the valve body down, he air-checked the K1 clutch (Figure 2), which seemed to be good. This narrowed it down to the valve body or the solenoid. There are three valves involved in the control of the K1 clutch. Fluid comes from the manual valve to the B1 relay valve (Figure 3), then through the K1 regulator valve (Figure 4), which is controlled by the N92 solenoid. From the K1 regulator to the K1 switch valve (Figure 4), then to the K1 clutch. I sent him a valve body breakdown so he could check these valves and discussed some methods of checking the valves with the valve body disassembled. I also wanted him to check it with the valve body halves bolted together, and the end plugs and solenoid left out to stroke the valves with the valve body assembled to make sure there is no issue of valve body warpage locking down the valves while torqued.

He checked all the valves and found they would drop in the bores by gravity. This meant the solenoid had to be the problem. He found he could not buy the solenoid separately. He had to purchase a new valve body, which included solenoids. He did not like the price. So, he called to see if I might have any good used ones lying around. I rarely work on these 09Ds and didn’t have any parts, new or used, in stock. I recommended he check into a Transgo kit that had the caps for the solenoids so he could clean it out and maybe get lucky. Other than that, he would have to do some searching online in places such as eBay because, at that time, none of the parts companies had any in stock.

He called back a couple of days later to let me know he got the Transgo kit. And while he had the solenoid apart, he found the armature was sticking slightly. The transmission worked like new after cleaning the solenoid and installing the valve body back into the vehicle. He was extremely happy to save a bunch of money and see his daughter back on the road.