Dealing with faults in the high voltage (HV) systems isn’t hard, but you do need to be aware of the dangers involved. Make sure you understand what is needed before attempting any diagnosis or making any HV repairs on hybrid vehicles. Precautions must be taken before attempting to diagnose or repair any component that has orange or blue high voltage wires connected to it.
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Training is very important, because it will provide you with the safety and repair information that you need to diagnose and repair hybrid vehicles. I suggest that you attend a good hands-on class that will allow you to experience using different information systems, equipment, factory and aftermarket scan tools, meters and scopes, just to name a few.
The question is how do you know it’s good training or just hype? There always is someone telling you they’re the best, and when you go to their class it’s less than you paid for. Be sure you do your homework before you spend your hard-earned money. Talk to other techs that have attended different programs to see what they thought of the instructor and the material.
Special safety gloves should be worn anytime you’re working with HV components. Safety gloves must be rated for 1,000 volts/Class 0, and with covers they’ll cost about $110 or so. You should them whenever they might have been compromised or they reach the expiration date stamped on them. Your safety, even your life, depends on these gloves as well as other safety equipment.
Cost for recertification is approximately $25, and turnaround time is a few days. Always wear these HV gloves when working on any high-voltage part of the vehicle or until the high voltage has been disabled. A word of caution: The HV battery always has power, just like 12-volt battery under the hood. Make sure to check the HV glove covers (outer leather covers) for any cuts or holes. Follow that up by checking the HV gloves themselves for pinholes by using the roll up test (capture air in the glove while rolling it up). If you think the glove has been compromised in any way, send it out to be professionally tested rather than risking a serious accident.
Also, it always is a good idea to wear safety goggles to protect your eyes.
In addition to gloves and eye protection, you will need a yellow “pull pole” or “rescue pole.” This is a must have in a shop that is working on hybrid vehicles. It’s an insulated hook that’s used to pull someone that is being electrocuted off the high voltage vehicle he/she is working on.
Make sure to chock the wheels of any hybrid you’re working on. Hybrid electric drives are silent and will move without making any noise. Think of it as a golf cart, silent and potentially deadly. Install wheel chocks on a minimum of one wheel to prevent vehicle movement.
Use a Megameter insulation tester to test cables and electric motors. The meter reads ohms from 0.01 MΩ (megaohms) to 2 GΩ (gigaohms) and performs insulation tests with 50, 100, 250, 500 (default) and 1,000 V source. Use only a CAT III certified digital volt-ohmmeter (DVOM) on all cables, capacitors and high-voltage batteries. Other meters are insufficient for the task, and all you need to do is take a look at some of the pictures of blown meters on the Internet to know you don’t want to be the one holding it when it explodes.
Make sure that you have a labscope that can handle the high voltage, such as Fluke, EScope with special CAT III leads or PICO, also with a special lead kit.
Of course, you’ll need a scan tool capable of accessing the HV data parameter identifiers (PIDs). Many aftermarket tools are capable of displaying these PIDS, and of course you always can consider adding OE tooling to ensure you have the information access and bi-directional capabilities you might need.
An HV battery tester and charger is something you also will want to invest in. Hybrid vehicles are getting older, and as they age, problems develop. High-voltage batteries have a problem with holding their charge levels, and the individual cells that make up the battery pack can age differently, resulting in imbalance in the assembly. There are a couple of ways to go forward in this area. One is to purchase an inexpensive battery load tester and a good battery charger designed for use with HV batteries. I also recommend using a temperature gun and small cooling fan to make sure the batteries do not get too hot while charging. Total cost of all the equipment that I use is about $1,000.
Information is something that you need to make a successful diagnosis and repair. Most aftermarket service information systems will have the information you need to tackle the majority of HV problems. Identifix, iATN and Google are other good sources that might help you. Just be sure to consider the source whenever relying on a generic Internet search. If you want the same information the dealer techs are accessing, log on to www.OEM1Stop.com and then select the OE you want from the list to be taken directly to the factory service information site. Some hybrid info is available for free, while full access for most OEM sites is offered at a nominal cost.
Remember, high voltage orange or blue cables run under hybrid vehicles from their engine compartment to the rear of the vehicle. They often are hidden under thin plastic or sheet metal covers. Be aware that setting the lift wrong can do major damage to the HV system and may also result in personal injury. Consult your service information for correct lift points.
Tires should be rotated every 5,000 to 6,000 miles. Make sure that the correct tires (made for hybrid vehicles) are installed on the vehicle. A common mistake is installing the wrong tires (non-low rolling resistance tires) resulting in a decrease in fuel mileage. When you are checking the tires, you also can check the brakes for signs of rust on the front and back of the rotors. Rusted rotors are common, because the pads are not used all that much do to regenerative braking. It’s a good idea to clean up the rusted rotors with a sanding disk and check the brake hardware for rusting, cleaning and lubricating as necessary.
Hybrid batteries and other HV components can overheat quickly if not cooled. Some vehicles use the A/C system to provide cooling, making that system more than just a convenience for passenger comfort. Others have air inlets to the cabin that must remain unobstructed, including dedicated cabin filters that should be checked and replaced if dirty.
A Real World Repair
The first vehicle is a 2009 Honda Civic Hybrid with 35,495 miles. The customer was complaining of low power, poor fuel mileage and poor performance. The first thing I did was interview her, asking if this was something that just happened, was it on flat or hilly roads, temperature effected, did she notice the HV battery level and were any dash lights on. The answers to all the questions was “yes,” so I connected my scan tool and scanned the vehicle’s computers.
The result was a P0A7F diagnostic trouble code (DTC) “Battery Module Deterioration” explaining the illuminated Integrated Motor Assist (IMA) fault light displayed on the instrument cluster. Having come across this DTC before, I knew that there were multiple fixes, so I checked my service information system for Technical Service Bulletins (TSBs) to see which ones might apply.
The one I found recommended reflashing the Motor Control Module (MCM) and maybe replacing the HV battery pack. I proceeded to install the new software and perform a HV battery charge/rebalance.
There are a couple ways to perform the charge/rebalance of the HV battery pack. The rebalance can be easy or hard to perform, so I chose the easiest way, which involves either using your scan tool or on some vehicles removing the fuse that powers the MCM. The other method is more involved and requires removing the battery pack and discharging each stick (cell) and then recharging them. The discharger cycle helps isolate and identify the weakest sticks and may require them to be charged and discharged multiple times. You need special training and equipment to perform this procedure. I decided to go with the easy charge/rebalance, especially because this vehicle had low mileage and at the time was only a year and a half old.
I knew that if the owner went back to the dealer, the dealer would try the easiest repair first, a reflash and HV charge/rebalance of the battery pack. The dealer most likely would change the HV battery only if the easy HV charge/rebalance did not work.
To fix this problem I reset the MCM in order to reset the battery pack memory. My next step was to race the engine up to 3,500 rpms until the HV battery meter on the dash reached the full mark. Once the battery reached the full mark. I did the same reset procedure to the MCM two more times before taking the vehicle for a test drive. That‘s all it took to fix this problem Honda hybrid and make the customer happy.
Another Example
Our next problem vehicle was a 2008 Ford Escape 4X4 Hybrid with 89,296 on it and a warning message of "High Motor Temperature — STOP SAFELY NOW" on the odometer display.
The owner of this vehicle was driving along normally when he noticed the vehicle slowing down due to a power loss. The dash was lit up with a malfunction indicator lamp (MIL) and the dreaded red triangle along with the messages in the odometer display. He moved the vehicle off to the right of the road and shut the engine off. The vehicle owner opened the hood, check all the fluids and found nothing abnormal. He then tried to restart the engine but nothing happened.
The hybrid Motor Generator (MG) on this vehicle starts the engine. He thought that the HV shut-off switch might have tripped, but it did not. The HV shut-off switch is just like the Ford fuel pump Inertia switch. Its purpose is to shut off the power if the vehicle is involved in an accident.
Enough time went by to allow the MG electronics to cool down and the engine finally restarted. He drove the vehicle down to my training center just in the nick of time, because the vehicle was about to shut off again. While this problem was related to the HV system, an HV component did not cause it. The problem that causes this is related to the inverter cooling pump not working right, or worn to the point of not working at all. The pump’s job is to flow coolant and keep the HV electronics from getting too hot. The HV system protects itself by displaying the message while reducing power before finally shutting down the power. The fix for this vehicle was a piece of cake. All I had to do is unbolt the old pump, install the new one, refill with the Ford proper coolant, bleed the HV cooling system and clear the DTCs. This vehicle was now ready to go back on the road.
A Final Example
Our last problem vehicle is a 2001 Prius whose dash looked like a Christmas tree display besides exhibiting poor mileage and performance. The scan tool displayed a P3000 HV Battery Malfunction DTC along with low HV battery block voltage. This is a common problem on the GEN 1 Prius, because the batteries are of the old design and are known to fail.
My next step would be explaining to the vehicle owner the problem with their HV battery and preparing them for a very expensive repair. Beacuse the vehicle owner already had taken the vehicle to the Toyota dealer, the HV battery problem was not a shock to him. He explained that the dealer provided him with an estimate of $4,200 plus possible extras. Now my job was to explain to and convince him that I was capable of repairing his Prius.
The repair would involve rebuilding his HV battery pack, clearing DTCs and balancing the battery pack. I explained I would be able to do the repair and guarantee it for a reasonable price that would be considerably lower than the dealer. Once he agreed, I removed the 100-pound HV battery from the vehicle. The next step was to load test and possibly charge each of the 19 packs/38 cells if they were good enough.
The HV battery should have a total of approximately 274 volts. I found the copper bus bar and terminal ends connections total corroded as well as leaking batteries. With most of the cells leaking, that ruled out using them. So I tested only the ones that were not leaking. I had some good GEN 1 HV battery cells in stock that I tested, loaded and retested a few times.
Donor cells (good used) are the best way to rebuild this HV battery pack while keeping the DTC from coming back. Why not use new HV cells? One reason is new cells can cause a HV battery imbalance problem. The other reason was at the time Toyota did not sell HV cells or battery packs to the aftermarket. I believe that has changed, but I still prefer using good used cells to rebuild the HV battery saving the owner money and making me more profit.
Because my HV battery was able to hold a good charge after a few discharge/charge cycles I installed it in the vehicle, cleared all DTCs, started the vehicle up and test drove. The vehicle is still running well three-plus years later.
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