Adapted from Larry Carley’s article in Underhood Service.
As more and more hybrid electric vehicles are bought by the motoring public, technicians who understand how to properly service these vehicles will be in high demand at independent repair shops and dealerships. While this article will give you some basics to HEV technology, plan to get some specialized HEV training if you want to make this your career choice.
Hitting the Streets
The Toyota Prius and Honda Insight hybrids have been around since 2001; the Honda Accord, Ford Escape and Lexus RX 400h hybrids since 2005; the Honda Civic, Toyota Highlander, Mercury Mariner, Chevrolet Silverado and GMC Sierra hybrids since 2006; and the Lexus GS 450h, Saturn VUE Green Line, Toyota Camry and Nissan Altima hybrids since model year 2007. In 2008, manufacturers launched the Saturn Aura Green Line, Lexus LS600h, Mazda Tribute, Chevrolet Tahoe, GMC Yukon and Dodge Durango hybrids and there are more than a dozen new hybrid models coming for model year 2009.
The hybrid market is still quite limited with less than 1 million hybrid vehicles on the road, but some experts say that within five years, 20% to 25% of all new car and light truck sales will have hybrid powertrains especially if gasoline prices remain high.
Hybrids are proving to be quite popular with motorists because of the improved fuel economy they deliver. By reducing the “on” time of the engine and using battery power as much as possible for low speed stop-and-go city
driving, hybrid vehicles can achieve impressive fuel economy numbers.
The 2007 Toyota Prius has EPA fuel economy ratings of 60 mpg city, and 51 mpg highway. The hybrid versions
of the Chevy and GMC sport utility vehicles get 25 to 30% better fuel economy than their conventional counterparts.
What makes Them Different?
A hybrid vehicle is essentially the same as any other vehicle except for the extra high-voltage hybrid hardware. On a full hybrid, such as the Toyota Prius or Ford Escape, this includes a unique continuously variable transmission, two electric motors, an integrated starter/alternator in the flywheel, various electronic control modules, and a high-voltage battery pack in the rear of the car.
On “partial” hybrids, such as the Saturn VUE Green Line, that do not have a full-electric mode, the only significant difference is the belt-driven starter/alternator that is used for start-stop driving and to recharge the hybrid battery in the back.
The main difference between all hybrids and other vehicles is that high-voltage hybrid battery, which is usually mounted in the rear of the vehicle. The voltage output of a hybrid battery depends on the vehicle. On a Honda Insight, the hybrid battery is 144 volts. On a first generation 2001-’03 Toyota Prius, the hybrid battery is rated at 276 volts, and 201 volts on a second generation Prius (2004 and up). On a Ford Escape, the hybrid battery is 300 volts.
Warning: This kind of voltage can be deadly and must be treated with respect. If you think a shock from a spark plug wire is bad, a shock from one of these batteries can kill you in a split-second!
The hybrid batteries that are used in current generation vehicles are nickel metal hydride (NiMH) and consist of many individual cells wired together in series. To protect the vehicle’s occupants and service technicians from the high-voltage hazard, the hybrid power circuit is heavily insulated and is usually color-coded orange.
So if you see a heavy orange cable snaking under a vehicle or in the engine compartment, it is carrying the hybrid’s high-voltage current. The circuit may or may not be hot even when the engine is off, so treat all orange cabling with caution.
Hybrids still have an ordinary 12-volt battery for powering the ignition system, fuel pump, lights and other electrical accessories on the vehicle. But in the case of the Toyota Prius, the 12-volt battery uses an oddball post configuration that is smaller than standard posts, and the battery is located in the trunk.
No special precautions are required when replacing most maintenance or repair parts on the non-hybrid components in the vehicle. But if any repair work involves hybrid electrical or powertrain components, the hybrid battery must be disconnected prior to touching anything that might carry high voltage.
The procedure for isolating the hybrid battery varies depending on the vehicle, but typically involves flipping a switch on the hybrid battery pack or disconnecting a battery cable or fuse. On a first generation Toyota Prius, the hybrid battery is disconnected by opening the trunk, removing the liner from the left front corner, and pulling straight back on a small orange handle to remove the battery connection plug.
Warning: Always refer to the vehicle manufacturer’s recommended disconnect procedure. Wearing protective rubber gloves that are rated to withstand up to 1,000 volts is also recommended for added protection. Also, don’t touch any high-voltage components for at least 10 minutes after disconnecting the battery. This gives the high-voltage capacitors in the hybrid control system time to discharge.
Actually, hybrid vehicles are not as dangerous to work on as they might seem at first. If the key is off and the key is out of the vehicle, the hybrid system is powered down. The battery can’t shock anyone unless they go poking around the high-voltage battery connections with bare hands or uninsulated tools. Even so, there are some hidden dangers with these vehicles.
When the key is in the ignition (or the keyless entry fob is inside the car), and the “Power” button is pushed on a Toyota Prius, a “Ready” light on the dash comes on. This means the hybrid powertrain is active and is ready to go even though the engine is not running and the car isn’t making any noise that would indicate it is on. So when the Ready light is on, the engine may suddenly start itself without warning if the hybrid battery is low and needs to be recharged.
This presents no danger to the driver because the car won’t go anywhere unless it is in drive or reverse, but it could be a hazard to someone if they were working under the hood and didn’t realize the Ready light was on. So always make sure the Ready light is out before doing any routine maintenance or repairs.
Hybrid Battery Life Expectancy
One question many people who own a hybrid or who are thinking about buying a new or used hybrid have is the durability of the hybrid battery. On a Toyota Prius or Ford Escape, the factory warranty on the hybrid battery and other hybrid powertrain components is eight years or 80,000 miles, or 10 years and 150,000 miles if you live in California.
The actual design life of the battery, according to Toyota, is 15 years and more than 200,000 miles.
So far, the hybrid batteries have proven to be extremely reliable and trouble-free which is a good thing because (1) the hybrid batteries are only available from car dealers, and (2) they are very expensive. The current list price of a replacement hybrid battery for a Toyota Prius is $2,985!
Hybrid batteries generate a lot of heat and require extra cooling. Most hybrids have some type of special venting for the battery pack, which may even include a separate cabin air filter (Ford Escape, for example). On the Prius, there is a cooling fan for the battery inside the right rear trim panel, and two battery temperature sensors in the hybrid battery compartment.
In theory, a hybrid battery should never run down. The control module should start and run the engine to maintain battery charge anytime the battery drops below a certain voltage. But if a vehicle is not driven very often, sits for weeks at a time in a garage, or has a problem that drains the battery or prevents the engine from running to recharge the battery, the hybrid battery can go dead. If this happens, a special jump start procedure or charging procedure may be required to get the vehicle moving.
On a Prius, there is a special jumper connection under the power distribution center cover in the engine compartment. A 12-volt battery charger can be used to boost the regular 12-volt battery enough to start the engine (Toyota recommends using their special 12-volt charger instead of a conventional 12-volt battery charger).
Once the engine is running, it should be left running for at least 30 minutes to recharge the hybrid battery. No attempt should be made to recharge or jump start the high-voltage hybrid battery directly.
Did you know…
As for faults that involve the hybrid system (things like the car won’t start, it stalls or doesn’t run right, battery problems, etc.), you need to be up to speed on hybrid technology, and have access to the factory service information either via the OEM technical website online or aftermarket information providers.
Diagnosing a Hybrid
Hybrid vehicles have the same onboard diagnostics as every other vehicle built since 1996. You can access fault codes, freeze-frame data, sensor inputs and various self-tests with a scan tool provided the scan tool is up-to-date with the latest software for the year/make and model of vehicle you are trying to diagnose.
If a problem occurs with something that is not part of the hybrid system, diagnostics is essentially the same as on any other vehicle. You troubleshoot the fault, do your diagnostic tests to rule out various possibilities, and hopefully zero in on the faulty component that needs to be replaced. Whether you have a P0300 random misfire code or an O2 sensor code, the diagnostics would be essentially the same as on any other gasoline engine.
Now let’s get up close on a common HEV Toyota’s first entry in the hybrid market the Prius. To access the onboard diagnostics you need a scan tool, preferably a high-end professional-grade scan tool with software that can access most of the PIDs and self-tests that are available on the Toyota factory scan tool. If you do a lot of Toyota work, it would probably pay to invest in a Toyota scan tool so you have the exact same diagnostic access and test capabilities as a Toyota dealer technician.
If the Malfunction Indicator Lamp (MIL) is on, you’ll want to plug in your scan tool to read the code(s) and any freeze-frame data that might have been captured to help you in your diagnosis. Then, depending on what the code is, you’ll want to look at various related PIDs to see what’s going on with the sensors and system controls.
Problem areas that are going to require some hybrid know-how include any faults related to the high-voltage battery or charging system, any faults related to engine cranking, any faults related to the transmission, or any faults related to the hybrid control system.
Like other manufacturers, Toyota provides detailed diagnostic charts for all their fault codes. The charts include a description of the fault, the components involved, wiring diagrams and step-by-step checks that need to be made to isolate the fault.
Technical Service Bulletins
For faults that may not set a code, or for specific faults that seem especially troublesome or common, you should check to see if the manufacturer has issued a technical service bulletin. There are several such bulletins out on the Prius:
EG021-02 2001-’02 Prius, the MIL may come on and set a DTC P3125, which is an inverter malfunction code. The problem may be caused by a fault in the electronic control unit (ECU) or the hybrid inverter/converter assembly.
The bulletin advises using a scan tool to read the freeze-frame data for the vehicle speed that was recorded when the fault occurred (typically between 25 and 44 mph), the acceleration sensor value (in percent), reading the MG2 motor speed (in rpm), doing some math to convert the MG2 recorded rpm to vehicle speed, and comparing the results to see where the error occurred. If the recorded vehicle speed is higher than the converted speed value from the MG2 reading, the ECU is at fault and needs to be replaced.
Like we said, this stuff gets rather complicated so you need to read the entire service bulletin, be familiar with the various hybrid components, and have a scan tool that can read the proper PIDs and freeze-frame data.
In this case, if the ECU needs to be replaced, it is located under the passenger side kick panel. Before you touch anything though, you first need to disconnect the negative battery cable from the 12-volt battery in the trunk (which Toyota calls the “auxiliary” battery). You can now uncover and replace the ECU.
Like most late-model cars, if you replace the ECU, the computer has to undergo an immobilizer key code registration procedure. On the Prius, you connect a 12-volt battery charger to the 12-volt battery, set the parking brake, place the transmission in park, insert the ignition key and turn on the ignition. Then you leave it on for at least 30 minutes. The computer will recognize the key, sync itself with the key and reset the immobilizer code.
After 30 minutes, you can turn off the key and you’re done. The Ready light should now come on when the key is inserted and turned on while holding your foot on the brake pedal.
EG022-04 2001-’03 Prius. The MIL may come on and set a DTC P3130, and maybe also a DTC P3125, which are codes for a power problem or the Ready light not coming on. The fault may occur after the vehicle has been subjected to prolonged driving in heavy stop-and-go traffic, or when it has been driven at sustained high speeds during hot weather. The problem may be an overheated inverter/converter due to loss of coolant or coolant not circulating properly in the inverter/converter cooling system.
Because the inverter/converter is part of the high-voltage system, you do not want to touch anything until the high-voltage hybrid battery has been disconnected by pulling out the power service plug in the trunk. You then must wait at least five minutes for the high-voltage capacitors in the inverter/converter to discharge before proceeding with repairs to the cooling system or inverter/converter assembly. The bulletin covers how to drain, refill and bleed the cooling system, and the replacement of the inverter/converter assembly.
PG002-06 This bulletin covers precautions for removing or installing the inverter/converter assembly on 2001-’06 Prius, and 2006 Highlander and 2007 Camry hybrids. Basically, it tells you to disconnect the high-voltage hybrid battery before doing any repairs, to wear insulated rubber gloves before touching any high-voltage components, to wait five minutes after disconnecting the battery on the Prius and Highlander, and 10 minutes after disconnecting the battery on the Camry for the capacitors to discharge, and how to service the components in the inverter/converter cooling system.
Recall 06V266000 A recall of 2001-’02 Prius models for the free replacement of a possible defective crankshaft position sensor that could cause the engine to stall and not restart.