Entering the realm of hybrid repair can be a daunting venture for many technicians and shop owners. Servicing Honda Integrated Motor Assist (IMA) vehicles is a great way to get your feet wet, as the technology on these vehicles is intentionally not as evolved as competing manufacturers’ hybrid platforms. Understanding the system’s operation and recognizing service and repair concerns will help you in your quest to become a hybrid-capable repair technician or facility.
The IMA motor-generator is the heart of Honda’s IMA System.
Honda introduced its IMA system with the 1999 Insight and beat the competing Toyota Prius to the market by a margin of more than a year. Honda’s approach to the Hybrid Electric Vehicle (HEV) platform was to improve fuel economy by designing a lightweight, low-cost vehicle with an electrically assisted internal combustion engine (ICE). The IMA system utilizes a three-phase AC motor-generator (MG) sandwiched between the ICE and the CVT transmission.
This design is considered a simple or parallel hybrid and separates the IMA from its heavier Toyota counterpart that utilizes two motor-generators within a hybrid transaxle. The use of only one MG unit allows for the use of a fairly small HV battery, which also contributes to its weight reduction. The IMA has been used successfully in the Insight, Civic and Accord platforms, but because of increased EPA fuel economy demands, it will be replaced by a dual motor-generator hybrid drive, similar to Toyota’s Hybrid Synergy Drive system, in the 2014 Accord.
IMA Overview
Before you commit to servicing or repairing IMA vehicles, it is important to have a basic knowledge of system operation. The heart of the IMA system is a brushless three-phase AC motor-generator contained in a housing that bolts up between the ICE and the Constantly Variable (CVT) transmission. The rotor is a permanent magnet type that is bolted directly to the crankshaft, which means anytime the crankshaft turns, so does the rotor. The IMA motor provides power assist when needed, and also takes on the role of the conventional starter motor and alternator. The rotor includes a tone ring, and the IMA position sensor contained within the IMA housing monitors it.
Lineman’s gloves are essential personal protective equipment for HV repairs.
Control of the motor takes place in the Integrated Power Unit (IPU), which is located along with the HV battery behind the rear seat. The IPU is the brain of the IMA system and includes the Motor Control Module (MCM). The MCM monitors HV system data and controls the motor-generator through a series of contactors that act as oversized relays to allow the flow of high voltage to and from the IMA motor to either power the motor during assist or recharge the HV battery during deceleration. In addition to monitoring HV voltage output and input, the IPU also controls the high voltage air conditioning compressor and charges the 12-volt battery via the Motor Power Inverter (MPI).
The 12-volt battery, although not primarily used for starting purposes, still plays an important role in the vehicle, as it powers all control modules and related components including the HV system modules. It’s also required to provide power to the 12-volt backup starter motor. One other key player in the IMA system is the Battery Control Module, which we will discuss in further detail later. All of these components work together to give the IMA system several distinct modes of operation:
• Assist – Provides assist to the ICE by adding horsepower and reducing fuel consumption.
• Charging – Charging happens on deceleration, also known as regenerative braking.
• Auto Idle stop – ICE turns off when it sees the brake pedal depressed and restarts when the pedal is released. If the pedal is depressed for longer than 90 seconds the ICE will restart to continue charging the 12-volt system.
• Electric propulsion mode – Cylinders are deactivated via the V-TEC system. The ICE crankshaft continues to move with the IMA motor but all the valves are held closed as the pistons move in the cylinders.
All of these modes of operation would not be possible without the use of high-speed communication networks. The IMA system utilizes Controller Area Network protocol (CAN), and Honda refers to these networks as F-CAN, or “fast” CAN, and IMA CAN.
To check gloves for pinholes, roll gloves from the cuff as shown and listen/look closely for leaks.
For more details on IMA system operating strategies you may want to have a look at Honda’s two corporate websites. First is www.world.honda.com. If you do a quick search for “hybrid system” there, you will be linked to several great articles with illustrations and animations.
Second is www.techinfo.honda.com. This is Honda’s independent repair website that provides free of charge hybrid emergency response guides which are a great look into Honda IMA operation and safety. This site also offers subscription packages for Honda’s service express and ISIS information systems. At a subscription rate of $20 per day, $100 per month or even $1,000 per year, this is a good resource for repair situations that call for factory direct information.
Keep in mind that Honda ISIS has technical service bulletins (TSBs) that are updated daily, which can play a key role in helping you get IMA concerns fixed right the first time. Honda also provides some subscription based e-learning style training here that is extremely helpful in understanding hybrid related vehicle systems such as communication networks, Variable Cylinder Management, as well as V-TEC, all of which play a vital role in the IMA system. Training modules are available on the site relatively inexpensively and are well worth the investment.
What You’ll Need
Now that we have a general idea of how the system functions lets look at some critical service equipment. Servicing these vehicles requires some must-have equipment but getting started might not be as expensive as you think.
Leather shells that go over the HV gloves will help protect both you and the gloves.
Safety Equipment – Though it has been covered here in Motor Age in the past, it always is important to remember proper safety procedures, as high voltage always presents the risk of electrocution and even death. Always follow the repair manual guidelines and recommendations for when to use appropriate safety equipment. As with all HEV/EV service, you will need to have a good set of high voltage lineman’s gloves with leather glove shells to go over them. Be sure that the gloves are rated to 1,000 volts and are within the acceptable six-month certifications date found on the cuff. Also be sure to check the gloves for pinholes and cracks.
Do not blow into the glove but instead roll the glove up at the cuff and listen for leaks. If you are unsure as to the condition of the gloves, don’t take a chance. Keep in mind that on hot and humid days it’s important to keep sweat from dripping from your arms and down the gloves. Sweat is a capable conductor of electricity and can enable high voltage to find a path to ground through your body. Wear cotton glove liners and long sleeves if necessary to prevent this from occurring. Also be sure to wear protective eyewear and keep loose jewelry, keys and lanyards in your toolbox. Leave nothing to chance.
Insulated tools – Honda recommends the use of insulated tools for hybrid battery service. Even when the HV system is switched off there is a chance for electric shock, as some of the hardware on the battery is still considered “live.” If you are going to be offering battery replacement service for your Honda hybrid customers, you will want to look into getting yourself a set of these insulated tools. Follow service information directions and proceed with caution.
Be sure your meter is rated for high voltage.
3. Digital Meters – A good meter is essential in hybrid service. You will want to have a meter (and leads) that is rated at 1,000 Volts Cat III/600 Volts Cat IV. Most professional level meters meet this standard, but check with your meter manufacturer if you are unsure. There is no need to purchase a specific “hybrid” meter unless you are purchasing an insulation tester to test motors for insulation faults.
4. Scan Tools – When entering the realm of Honda IMA service it’s important to make sure you have the scan tools and subscriptions to get the job done. If you are using an aftermarket scan tool, be sure that the tool can communicate with the Motor Control Module and Battery Control Module. Some aftermarket tools provide great coverage here, while some leave a lot to be desired. Be certain that your tool is capable before you commit to a repair and get yourself in a bind. Having Honda’s Modular Vehicle Communications Interface (MVCI, available through SPX), a laptop and a subscription to the Honda Diagnostic Software (HDS) would be extremely helpful and in some cases necessary here. In many cases, IMA repairs will require reprogramming that is not possible with J-2534, so again be sure you verify that your tool can do the job before you commit yourself. The MVCI with and HDS subscription is certain to get the job done.
Training – Anyone can buy the tools and equipment needed to service hybrid vehicles, but owning them and knowing how to use the safely and effectively takes training specific to the hybrid models you want to service. Honda has online training modules that are designed for their dealer technicians, and might leave out vitally important details they assume their techs should already know. If you’re new to hybrid service, invest the time and money in a hands-on training program before you tackle any type of service on a high voltage system.
Common Service Issues
Once you have the essential tools and training, you can feel confident in approaching IMA service. Now the fun part is looking at some service concerns that are sure to come through your doors.
When working with high voltage components such as the HV battery, IPU assembly, IMA motor or HV wiring (identifiable by its bright orange loom), you will need to deactivate the high voltage system. This can be done by removing the rear seat back, removing the switch cover bolt with a 10 mm socket and flipping the switch to the “off” position. The HV shutdown also will need to be performed when removing or installing the engine or transmission. If you are unsure of when to perform the HV shut-down, consult the service information. HV shutdown for routine maintenance is not required and you can feel comfortable working safely on other systems around the vehicle. Also keep in mind that the brake system does not require any special shutdown procedure for service.
Honda had some early issues with its HV batteries and battery monitoring strategies. HV battery concerns are not all that different from concerns with 12-volt batteries. Generally speaking, low temperatures result in poor battery performance, and high temperatures result in reduced battery service life. For this reason, Honda uses the Battery Control Module (BCM) to monitor battery voltage and temperature. Several updates to the software have been issued since the introduction of IMA in 1999 and improved BCM strategy has markedly improved battery life, yet here are still some concerns surrounding the control strategy. The BCM looks to see ideal battery temperatures, typically around room temperature. If temperatures are too cold or too hot, the BCM will disable the IMA system and the vehicle will rely strictly on the ICE, hence the need for the 12-volt starter.
The IMA Motor and housing is located between the ICE and the CVT transmission.
Often customers will complain of poor fuel economy in extreme cold or hot conditions, i.e. winter and summer. Unfortunately what they are experiencing is considered a normal condition and is a designed BCM strategy to prolong battery life. The battery relies on the vehicles HVAC system to warm or cool the battery and cabin air is ducted from the passenger compartment to the battery via a fan motor. Once the battery module sees the desired temperatures, the IMA system resumes its normal functions.
Another concern for independent shops is what to do with customer vehicles with battery complaints. Honda does not require specific testing or charging equipment. Instead it relies on the algorithm within the MCM and BCM to monitor battery condition and will illuminate the IMA warning icon on the instrument cluster when there is an IMA fault. If a customer complains of poor fuel economy but there are no codes, you typically have a fault other than the IMA system. The module strategies are fairly reliable and will even generate codes as specific as DTC - P0A7F “REPLACE BATTERY.” The concern for shops is what to do when they get this code.
IMA rotor removal requires a special pulling tool and includes a case to store the rotor while it’s removed.
When choosing to repair, rebuild or replace a battery there are a few things to take into consideration. The powertrain warranty on Honda vehicles does not cover the IMA battery. However, the battery is covered under the emissions warranty much in the same way that catalytic converters are. That warranty covers the battery for eight years/80,000 miles, and in some cases the batteries are covered under the California emissions standards warranty of 10 years/150,000 miles. Honda has a TSB addressing this from December 2012, and it has extended the warranties of some batteries to as much as 170,100 miles. Don’t be the shop with egg on its face that decides to repair, recharge or replace a battery that Honda should have to replace for free. Do some homework and have the Vehicle Identification Number (VIN) number searched through ISIS subscription or through your local dealer.
If battery replacement is necessary, you have a couple of options. You can repair your existing battery with known good parts from a donor battery, but this option leaves the most to chance in that you are asking your customer to rely on used parts. You could recondition the battery if you own the equipment. Another option is to go with a remanufactured battery, either through your local parts house or through Honda. Honda offers only remanufactured replacement batteries, so keep that in mind when making your decision. The cost of the battery from Honda is right around $2,000 depending on year, make and model.
The replacement of the battery is not labor intensive, but requires the transfer of the junction board from the old battery. Be sure to read up on the relative service bulletins regarding this procedure, as they vary between year and model. Again, make sure to pay close attention to safety instructions. After the battery is installed, you will have to program the specific battery software into the BCM. Be sure you have the capability to program unless you are prepared to send it to the dealer or have a mobile diagnostic service come in to do it for you.
Once removed the HV battery and IPU assembly are on the bench and ready for parts transfer to the remanufactured battery.
When performing the replacement of the engine, transmission or IMA motor, keep in mind that to remove the IMA rotor you will need a special puller tool (Honda PN – 08AAF-RCJA100). The tool comes with a case designed to store both the tool and the permanent magnet rotor while it’s removed and is intended to protect it from attracting metal particles or shavings that can damage or interfere with the motor or motor position sensor upon reinstallation. Removal of the rotor without the tool is nearly impossible and extremely dangerous. Keep in mind that if the permanent magnet rotor is spun within the stator you will induce high voltage into the windings of the motor that can result in serious injury or component damage. After engine, transmission or motor replacement, the motor position sensor will need to be relearned. Make sure your scan tool is up for the job.
Over the summer a friend was complaining about a significant drop in fuel economy. He went to the local Honda dealership, which found nothing wrong with the battery or IMA system. He recently had the tires replaced with some very high quality, name brand tires and found out that they were not the low rolling resistance (LRR) tires that Honda and many other manufacturers use on their hybrid platforms. LRR tires are designed to strike a balance between traction and low rolling resistance and are designed to further improve fuel economy. To be certain that the tires were the issue, he switched the wheels and tires for a set off another Honda IMA vehicle and fuel economy was restored. The difference in fuel economy was quite noticeable. Be sure to consult your tire provider and be sure to install LRR’s or you may be in line for a comeback.
We have looked at the basics of IMA repair and service but have only scratched the surface. Keep in mind that Honda technicians certified in IMA repair attend many weeks of hands-on training in subjects such basic and advanced electricity and engine performance before taking their hybrid specific classes. To stay ahead of the curve seek out and attend hands- on hybrid training through your local community college or training provider. With some foundational knowledge, a desire to learn new technology and the right tooling, you and your shop will be ready for IMA service and repair.
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