Handling hybrid repairs

Servicing hybrids requires a commitment to keeping up with the pace of evolving technology

The U.S. seems to be hybrid-crazed. Everywhere you look these days, hybrid-drive vehicles seem to be all the rage. This sensationalism certainly has grabbed a lot of media attention about the environmental aspects of hybrid technology.Despite all the fanfare, hybrid technology took it on the chin recently. Reports of battery fires on the highly touted Chevrolet Volt--punctuated by a full-blown investigation from the National Highway Transportation Safety Administration (NHTSA)--serve as a reminder that this technology is still emerging and you should stay on top of the latest developments.Although the Chevy Volt fires were linked to crash testing and not service procedures, they do suggest that a healthy amount of respect is in order for the batteries and high-voltage electrical system. With that as a backdrop, along with the growing numbers of hybrid vehicles, we bring you this issue’s Tool Q&A.

Q: We want to perform cooling system maintenance on hybrid vehicles. Are there any differences from regular cars and light trucks?

A: For the most part, the cooling system of hybrid vehicles is substantially identical to conventional vehicles, since hybrids use an internal combustion engine (ICE) as part of the drive system. You’ll find the typical array of radiator, pressure cap, reservoir, water pump and so forth. However, there may be differences on particular vehicles that you need to be aware of. For example, let’s say you’re diagnosing a no-heat or low-heat problem. Many hybrids use an electric assist pump to move coolant when the engine is in the idle stop mode. To be thorough, you’d need to include this assist pump in your diagnostic regimen to get to the heart of the problem.


Q: We run an air conditioning specialty shop. Do hybrids have any major differences in their A/C systems that require specialized equipment?

A: The air conditioning systems used on hybrid vehicles are virtually the same as conventional vehicles, with a few key exceptions. Since hybrid drive systems often employ the strategy of shutting down the engine when the vehicle stops, the compressors on these vehicles must have another type of drive system so that refrigerant flow doesn’t stop with the engine off (idle stop mode). Given this scenario, some hybrids use compressors driven exclusively by a high-voltage motor. In other applications, the compressor may use a conventional belt drive when the engine’s running, and then switch over to high-voltage electric drive when the engine’s off. Regardless, troubleshooting poor A/C performance on such a vehicle becomes more involved due to the change-up in compressor drive technology. In such applications, you’ll be required to use a scan tool to look at compressor engagement parameters and operation.


Q: When charging an A/C system on a hybrid, are there any special things to keep in mind?

A: First, make sure you refer to the system label that specifies refrigerant and refrigerant oil. The refrigerant is a no-brainer, since R-134a is the current refrigerant of choice. Refrigerant oil, however, is a different story. Hybrids with high-voltage electric drive compressors use special, non-conductive refrigerant oil that insulates the high-voltage motor. Make sure you use only what’s specified by the manufacturer. Both Honda and Toyota warn that using the wrong refrigerant oil—no matter how small the amount—compromises the insulation capabilities of the oil itself and increases the risk of high-voltage shock when working on the system. It can also trigger a diagnostic trouble code. Both manufacturers also caution that if the incorrect oil is added to the system, the main components of the entire system will need to be replaced. Finally, due to the the risk of cross-contamination of refrigerant oils, it’s best to keep a separate set of manifold gauges on hand to eliminate the chances of an oil mix-up.


Q: How do I determine which parts of the electrical system are high-voltage and low-voltage?

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