Prius P0A0F Code!
Imagine your cruising down the road singing at the top of your lungs to Tik Tok, your favorite Kesha song. Then unexpectedly every light on your dash comes on and your eyes focus on the large red triangle with an exclamation point in the middle. Panic washes over you as you consider all the issues that could cause it. The car keeps driving but you realize that the battery meter on the dash is slowly dropping. Suddenly the car shuts off and you have to coast to the curb. You try to start the car but nothing happens. Understandably your first instinct is to assume the hybrid battery is the culprit. After all, the red triangle of death appeared just before the car stalled, and the battery meter dropped to empty before the car stalled.
Assuming that the hybrid battery finally needs to be replaced is a completely reasonable conclusion to make. But it may not be your battery that is the problem. The red triangle, or the Triangle of Death, does not always mean the hybrid battery is the issue. It only means that there is a problem in the hybrid system. There are a litany of codes that can cause the red triangle to illuminate. In fact the scenario described earlier is more likely an issue where the internal combustion engine is not turning on. It is a fairly common issue where the Prius’ main computer (PCM), sees some sensor data and determines that it isn’t safe to turn on the engine. So the next few steps that play out is that the computer sets a code in the hybrid system (a P0A0F code), the red triangle comes on and because the engine isn’t coming on you will drive on the remaining charge of the hybrid battery until the car dies. And because the first conclusion you probably make is that the battery is bad you will naturally look at the state of charge meter on the dash and watch it drop to empty.
If the engine fails to start there are a couple common reasons for this issue. The first and most common reason is the Mass Air Flow Sensor (MAF). The MAF reads the amount of air coming into the engine. The computer (PCM) then uses that information to adjust how much gas to add to the mixture. If the MAF is dirty or damaged the computer (PCM) won’t be able to read the amount of air and will prevent the engine from starting. Sometimes simply cleaning the MAF and clearing the codes will solve the problem. Other times the sensor will need to be replaced.
The other common issue for the engine not starting is a loose vacuum hose. If the engine is pulling a lot of air in through a vacuum hose it will mean the engine has too much air and not enough gas. We call this running lean. When the computer reads that the engine is running too lean it will prevent the engine from starting to prevent damage. The most common time we see this is after an oil change. The technician doing the oil change will pull the air filter out to check it and will inadvertently pull a vacuum hose loose and never notice it. If the car stalled shortly after an oil change you might run into this issue.
Obviously this is just a couple of possible issues that can cause the red triangle to come on but it is a good reminder that there are other issues that can cause the light. And a lot of times they are a lot less costly than a new battery. Prius owner have been conditioned to assume that after 100,000 miles they need to be ready to replace their battery. So they (at least the customers we talk to) drive with a certain amount of anxiety that the battery will give out at any moment. Remember that its not guaranteed to be the battery and even if it is the battery there are cheaper options these days. A reconditioned battery through Atypical Batteries is usually a third of the price of a new battery. So relax, drive safe and don’t be embarrassed when you realize the neighboring car can definitely hear you singing!