What ATP Stands For (And Why Your Car May Have A Warning Light About It)

Whenever one of the common dashboard warning lights on your vehicle illuminate, like many drivers, you probably release an audible sigh. It's not that these warnings aren't helpful, but often they can result in an expensive trip to the mechanic. One of the less common indicators on select vehicles is labeled "ATP," and its meaning and function aren't readily known by most drivers. If you happen to see the ATP warning light activate on your instrument cluster, here is what it means and what its warning you.

ATP stands for automatic transmission park and it comes in automatic transmission 4x4 models where you can select between two and four-wheel drive modes via a transfer case. In 4x4 vehicles, there is typically a two-wheel drive setting, along with 4WD High, 4WD Low, and neutral. It's important to know the difference between 4WD High versus Low and when to use which 4x4 mode. Essentially, ATP is alerting you that your vehicle has a possibility of rolling even with your transmission in park and that the transfer case is set to neutral. As straightforward as an automatic transmission appears from the driving perspective, there are several complex processes taking place. In fact, there are likely many things you might not know about the gears in an automatic.

In four-wheel drive vehicles, there is a transfer case controlled by a switch, a dial, or a shifting knob around the center console to select either two- or four-wheel driving configurations. There are proper procedures for switching into these different modes. For example, when switching from 2WD to 4 High, Toyota recommends you slow to under 62 mph or more during colder temperatures, then turn the dial and check for a solid 4HI indicator light. However, switching into 4 Low, which is for rugged terrain requiring more torque, you need to be in neutral and stopped.

What happens if you don't follow the guidelines for changing modes on your transfer case? One driver in a Nissan Frontier found out after trying to switch into 4 Low to get up his slick and snowy driveway. He reported, "First time using 4LO, so I didn't know to wait (or shift to N) to allow xfer case to actually be in 4LO, aka the 4LO indicator steadily lit." What happened was an ATP warning lit up in his truck and was accompanied by an alert tone. The vehicle was alerting him that when shifting into park, since the transfer case was not fully locked into 4 Low, the vehicle would behave as if it was in neutral. With the transfer case effectively in neutral, even with the transmission in park, the vehicle has the capability to roll and is not safely stopped.