Tool Q&A: Want to do hybrid repairs?

Tools, equipment and advice from getting started with hybrid repairs to rebuilding HV batteries.


Editor's Note: The following is a revised version of the March Tool Q&A on hybrid repairs. Hybrid technology is new and evolving. In the interest of accuracy, PTEN offers a revised version of the March article. 

Q: What common tools do I need to get started?

A: Being that hybrids and electric vehicles (i.e. the Chevy Volt and Nissan Leaf) are made by mainstream companies, you will already have most of the tools you need. For example, hybrids generally have aluminum oil pans so you will need a torque wrench when tightening the drain plug. Even though the right scan tool with the appropriate OEM enhanced software is useful for any vehicle, it is absolutely necessary that the scan tool can communicate to the modules on a hybrid. 

The list of tools to work on hybrids that you don't have is probably small, but you should consider purchasing them if you intend to work on these vehicles. Safety equipment, first! You will need high voltage "lineman's" gloves capable of withstanding 1,000V of shock. The serious hybrid shop should have a pull-hook that looks like, but is fundamentally different from the hooks they have near pools to save drowning people. It is the only safe means of saving someone from electric shock. Not every dealer has one of these, however.

You will also need to upgrade your electric meter. To work on hybrids, you need to be able to diagnose HV leaks in cables and in internal windings inside the transmission and inverter. Only a Category III certified meter capable of doing an insulation test can get the job done.

Q: What am I commonly looking at when using my scan tool?

A: With the right scan tool (either factory or an aftermarket tool with strong OEM enhanced software -- believe it or not good aftermarket scan tools appear to communicate better with some hybrids), there are not that many PIDs (Parameters Identifications) in datastream you need to look for. Usually we communicate with the HV Battery Module, whose name changes depending upon the manufacturer, look at a few PIDs that concern battery state of charge and other relevant parameters. For example, the Toyota Prius with a bad HV battery often has a dozen good battery cells at 14.5V or so and only a few low ones, causing the module to throw a code.

Keep in mind that a pack with over 14V is not necessarily good. A single failed battery cell (this is common in Honda hybrids) can make the whole HV "defective" and have the vehicle throw a code.

Don't forget to check out battery temperature and state of charge PIDs as well. If the HV battery is too hot (example: a temperature consistently 100 degrees F on a Prius during normal operation) because of a broken cooling fan or something of the sort, this can cause HV deterioration. Furthermore, we are going to want to look at the state of charge of the HV battery to see if the motor generator is charging the battery pack as a whole. For example, it might be shown as a percentage on a Prius, so we would be looking for percentage to increase during charging conditions, such as rolling the car. This is different on a Civic hybrid, where we'd want to see the battery module output to be at least 144V and increasing during charging conditions.

Some experts believe that it is necessary to look at the state of charge of the HV battery to see if the motor generator is charging the battery pack as a whole. State of charge is constantly changing. You want to look at amps in and out of the pack to determine charging, if that PID is available. If it is not being charged, the motor generator is the least likely culprit since the software shuts down charging for many hybrid failure codes. This will depend on the code and the vehicle. It is wise at this point to consult test plans provided from the OEM to inform you where to go next.

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