Tech Tip: What can cause limited performance in a hybrid vehicle?

Oct. 13, 2014
Reduced performance in this case may be one or more issues. The two most common complaints are reduced fuel economy and reduced acceleration capability.

While performance may not be the first thing that comes to mind when you hear the work “hybrid” it is likely that you will eventually have one in your shop with a complaint of reduced performance. Reduced performance in this case may be one or more issues. The two most common complaints are reduced fuel economy and reduced acceleration capability. There are several systems that can have an impact on both of these.

The first one we’ll look at is the hybrid battery. A fuel economy decrease and/or a lack of acceleration can definitely be a sign of a failing battery. As batteries age they can have both power and energy related problems. One other battery related problem to consider before condemning the battery though is the battery cooling system. If the controller sees the battery temperature elevated above acceptable limits it will significantly reduce (if not eliminate) the electric assist. The controller does this to help protect the battery from overheating which can cause permanent battery damage.

Another area to consider if you have a hybrid vehicle performance issue is the motor/inverter cooling system. These complaints tend to me more common when a vehicle enters a limited performance mode after extended driving. In many cases after the vehicle has a chance to sit for a while the systems go back to normal operation. This can be caused by a fault in the motor/inverter cooling system. In most vehicles these are liquid cooled systems (Honda IMA units are the primary exception). The liquid coolant is typically circulated by 12V pumps to allow the heat to be dissipated to the air. These 12V coolant pumps have become a known problem for many manufactures, in fact there are several TSBs related to these problems. When diagnosing one of these systems keep in mind that much like a fuel pump these can suffer from low volume output as one failure mode. That means that even though the system appears to be flowing coolant the volume may not be sufficient to keep up with the heat being generated under certain conditions.

Information provided by: Automotive Research & Design (AR&D)

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