Last month we had a customer bring in his 2011 2.5 l Subaru Outback Limited with a continuously variable transmission (CVT).
The customer said the oil AT temp light (transmission temp), brake light, ABS light and traction control light all came on at the same time. That prompted him to pull over, shut off the car and then start it again. The warning lights didn’t come back on. The next day, however, they did when he started the car again. He also noticed the car would hesitate at higher speeds.
He dropped the car off at the shop and we connected it to the Subaru scanner. We pulled code P0971 (transfer solenoid circuit high). This code is stored in the transmission control module.
As I mentioned earlier, this car has a CVT transmission. It differs from a conventional transmission because it uses two cone-shaped pulleys instead of gears. The CVT was designed to make a much smoother acceleration, and it boosts fuel economy. Because the CVT has a smoother shift, it puts less load on the engine, thus slowing engine wear.
Diagnosing the problem
We started the diagnostics by checking the wire harness to the transmission. We wanted to make sure there was no fluid contamination inside the wire harness connector. Sometimes the seal where the wire harness comes out of the transmission will fail and transmission fluid will migrate through the harness and into the connector. The seal was intact and there was no fluid in the harness.
Next, we checked for power and ground at the transmission and at the transmission control module. Both were good.
We then used the scanner to communicate with the transmission. As we began to perform a communication test with the transmission valve body, we noticed that we could connect to the valve body but could not run any of the tests. The transmission control module sends signals to the transmission, but the valve body is what makes the transmission operate. At that point, we knew there was a strong possibility the problem was in the valve body.
Subaru has had quite a few problems with its CVT transmissions and in turn has extended warranties on quite a few cars. We then told the customer to contact the factory to find out if his car was under this extended transmission warranty. The customer called us back and said he was out of warranty by time and mileage.
We got authorization to drop the pan on the transmission and check the valve body. Once the pan was off, we checked the fluid and checked for metal in the pan. The fluid was not burnt and there was no metal in the pan. We then dropped the valve body and tested the solenoids (switches). We found one solenoid that had high resistance and one that was shorted. Unfortunately, Subaru does not sell the solenoids separately; you must buy the complete valve body. We then replaced it, and all was good.
The reason the oil AT temp light, brake light, ABS light and traction control light all came on at the same time is that all these systems are tied to the transmission. It just would have been nice if the solenoids were available separately.
Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call (650) 960-6988, email [email protected] or visit sunnyvaleforeigncar.com.
