Owners of Volvo cars equipped with Aisin AW55-50SN transmissions (and variations) are no strangers to faults. A little while ago I addressed issues with the valve bodies leading to hard shifting, and general rough operation. There is another common problem that plagues these cars, and it’s important to know the facts before panicking. When “Transmission Service Required” comes up in the information display, it can really ruin your day. This can be a few things, so it is important to be very careful if and when this happens. Sometimes this message is the sign of impending total transmission annihilation, meaning don’t drive it. However, most of the time, it can be much simpler. It’s important to immediately get the codes to know what you are dealing with, and when this 02 Volvo S60 AWD was displaying trans fault code 0039, it signaled that the valve body and the mechanicals were OK. Instead it was more likely to be the PNP Switch, affirmed by the Park, Drive, and Reverse display icons being replaced with a dash. Time for a DIY!
This particular PNP Switch DIY specifically pertains to the 01-07 S60, but it also applies to the V70, XC70 automatic, XC90 2.5T, and S80 5cyl 04-06, which may have different intake systems and cable routing but are otherwise the same.
The PNP switch is known by a few names. Neutral Safety Switch, or Transmission Gear Position Sensor are also common labels, but its task is simple. The PNP switch attaches between the main selector linkage and the selector shaft that goes into the transmission. In this position, it detects what shift mode you are selecting via the mechanical linkage, and clues in the various computers that executes the electronic side of the electromechanical operation of the transmission.
In short, when this switch goes bad, the electronic part of the auto trans is missing some key information. If it fails in a way where the switch never signals to the engine computer if the transmission is in neutral (or park), failure of this component can even lead to a no-start situation, since the computer would never give the go-ahead to try and start the car while still in gear.
This is a simple DIY with a basic tool set. You will need:
-a flat-head screwdriver…
-and a metric socket set.
To achieve this project, it should only take around an hour start to finish for the experienced mechanic, or more depending on your comfort level and mechanical ability.
If you have small hands, you can probably get away with straight replacing the switch. I opted to remove the air box and corresponding intake tubing to expose the sensor easily for filming.
The switch has some adjustability and calibration, but I personally found none of this necessary. If done by the book, you can plan on using some Volvo special tools to get the alignment perfect. The car has done thousands of miles with this repair (road trip!) and I can attest that this method works great. The car passed Massachusetts inspection with flying colors afterwards. Transmission shifts fine, no check engine light on.
eEuroparts carries a variety of Neutral Safety Switches, PNP Switches, and Transmission Gear Position Sensors, as this component is known to fail on many other cars, not just these Volvos in question.