Hybrid Service Is Not Rocket Science

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Hybrid Service Is Not Rocket Science

If you are turning over hybrid car repair to other shops, today’s the day to stop. Now is the time to invest in training and tools to work on these vehicles because the number of hybrids on the road is only going to grow. Make sure you can grab your share of this market by learning how to diagnose and correct the common hybrid vehicle’s service issues.

Most of the normal service and repair required by a hybrid vehicle is the same as other cars. They all need fluid changes and brake service, they all have oxygen sensors and EVAP systems and they use the same generic OBD-II fault codes as their non-hybrid cousins. But, of course, the hybrid powertrain and high-voltage battery add an extra layer of complexity, and most repairs for these systems require special tools, knowledge and information that are way beyond the scope of a magazine article. Most, but not all.

Hybrids are no harder to diagnose or repair than other vehicles; they’re just different. If you’re turning away customers because they drive hybrid cars, it’s time to invest in tools and training, because the fleet will keep growing and there’s money to be made. Meanwhile, here are a few common service items that are not at all difficult for experienced professional technicians with standard tools and a good service information system.

This article will focus on Toyota hybrid vehicles because they make up the bulk of the hybrid fleet.

Shift lever

A common problem with the second-generation Prius (2004 – 2009) is a shift lever malfunction. After “starting” the car (READY light on) and shifting into gear, the transmission immediately returns to Neutral regardless of how the lever is manipulated. Often it cannot be shifted back into Park, although rebooting the car (shut-down and restart) often gets it going again. This is usually the only symptom; there will be no fault codes or warning lights on the instrument panel. The fix is simple: replace the shift lever assembly and clear the shift lever memory by disconnecting the 12-volt auxiliary battery. The job requires the removal of four dash panels, three bolts and two connectors. See Toyota TSB-0142-11 for the latest part numbers.

Auxiliary battery

On a Prius, the traction motors and the A/C compressor are powered by the high-voltage battery pack. Everything else operates on 12 volts supplied by the auxiliary battery. This is an absorbed glass mat (AGM) battery mounted in the trunk. Like regular car batteries, AGM batteries still use lead/acid technology, but instead of plates in a bath of liquid electrolyte (flooded cell), there is a fiberglass mat between each lead plate and the electrolyte is absorbed into the mat. AGM batteries can deliver high current flow and they can tolerate deep discharging. They also can be sealed so they don’t emit hydrogen or acid fumes, but the charging current must be managed very carefully to avoid overheating.

The auxiliary battery powers all the control units, and the car won’t even turn on if that battery is dead. If the battery is low, the computers and control unit won’t get steady voltage and they become very unpredictable. That’s why the auxiliary battery is monitored constantly and a warning light is illuminated if it falls below 9.5 volts.

A good battery will show about 12.4 volts at rest and about 10.4 volts under maximum load. Since the auxiliary battery on a Gen II Prius is hard to reach, there is an easy way to test battery voltage and charging voltage from the driver’s seat.

Turn the headlights on, then put the car into READY mode and look for the warning light on the instrument panel. If the infamous “red triangle” stays on steadily, check for an error message on the display screen indicating a problem with the transmission. That’s a sure sign of a failing auxiliary battery.

The warning light may not turn on or it may appear for only a few seconds, so here’s how to check the voltage:

1. Turn the car on in Accessory mode (push the power button without pushing the brake).

2. Push and hold the Display button next to the display screen.

3. Turn the headlights on and off three times, and then release the Display button.

4. On the touch screen, select “Menu.”

5. Select “Display Check.”

6. Select “Vehicle Signal Check.”

While reading battery voltage on the screen, begin turning on lights and other electrical accessories to load the battery. If it drops below about 10.5 volts, the battery should be replaced. If you push the brake pedal and the power button again to go into READY mode, the battery will begin charging and you can see charging voltage: It should be about 14.2 volts even before the engine starts. Remember, the generator charges the high-voltage battery, and the voltage inverter takes power from the high-voltage battery to charge the auxiliary battery.

Hybrid drive battery

Right now there are two different battery technologies used in hybrid vehicles; nickel metal hydride (NiMH) and lithium ion (Li-ion). By 2013, most car manufacturers began switching over to Li-ion batteries because they can charge and discharge faster and they offer a higher power density (power per size/weight). However, Li-ion batteries can overheat dangerously if they’re overcharged, so the batteries must be carefully managed with sophisticated software. Since Toyota models with Li-ion batteries are still under warranty, we’ll discuss the NiMH batteries.

A high-voltage battery pack is made up of individual cells, or as Toyota calls them, battery modules. Their state-of-charge (SOC) is monitored constantly, and a fault code will be set if the PCM detects a module that is more than a few tenths of a volt different from the others (Li-ion battery modules are monitored to hundredths of a volt). A state-of-charge fault can be caused by corroded module connections or by failure of the module itself.

It’s rare for a whole battery pack to wear out or fail completely; it’s more common for individual modules to fail the SOC monitor. That said, the individual modules are pretty hardy, and most failures are due to overheating of the whole battery pack. They also fail due to lack of use: The battery packs in hybrid taxi cabs are generally lasting 300,000 miles, which is three times the factory warranty period (or twice the California warranty).

NOTE: If there are fault codes for the engine, those problems should be fixed first. Some engine management malfunctions will make the engine run longer or more often than normal to keep the battery charged.

The PCM monitors the voltage of each cell and the current flow of the whole battery pack. It also monitors the battery temperature, and one of the most important maintenance items in any hybrid vehicle is the battery cooling system. Toyota battery packs are air cooled by a squirrel-cage fan that draws air from the passenger cabin and exhausts it outside the vehicle (the Highlander hybrid has three fans). On earlier models there is no air filter on this system, and that has caused problems over the years. Fault codes PA080 and PA07F indicate high-voltage battery failure, but sometimes those codes are a symptom of overheating and can be cured just by cleaning the fan and air ducts.

Safety note

When working with the high-voltage system, the service plug must be removed to isolate the high-voltage battery. The plug is somewhere on the battery pack itself but its exact location is different on different models, so you’ll have to look it up in service information. The plug should be removed and placed on the dashboard of the car. This way everyone can see that it’s been removed and it stays with the car. When removing or installing the plug or the battery pack, wear Class 0 lineman’s gloves rated for 1,000 volts AC.

The battery modules in the first generation Prius (2001 – 2003) tend to leak electrolyte from a fill port on the module. It’s right next to the connection terminal, and it causes corrosion that can interfere with proper charging of the module and set battery fault codes. It also can provide a path from the high-voltage battery to chassis ground, which sets code P3009. Toyota launched a Special Service Campaign to repair the leak, and the 56-page service bulletin (SSC 40G) has all the instructions, illustrations and part numbers needed to complete the repair. The job is not difficult once the battery pack is removed, but a battery pack of that vintage is probably ready for retirement even if the vehicle itself has very low mileage. Reconditioned battery packs are available from aftermarket suppliers.

There are often symptoms of high-voltage battery problems before the warning light turns on. These include poor acceleration and reduced fuel economy as the engine runs longer to charge the battery. On the first drive cycle of the day, the charge indicator may fluctuate rapidly or show no/low charge. By the time the warning light turns on, the engine will be running almost constantly and the battery cooling fan will be operating at high speed all the time.

As noted earlier, aftermarket battery packs are available. Remanufactured batteries are built with modules reclaimed from cores and salvage yards. To get the best performance and avoid setting fault codes, the modules must be tested to match their charge/discharge capacities. It’s not hard, but to reduce the possibility of comebacks, most shops that service hybrid vehicles prefer to replace a whole battery pack instead of just a few failed modules.

The number of aftermarket battery pack suppliers seems to be increasing, and some are well-known companies offering warranties similar to OEM replacement parts.

As we said earlier, hybrid cars aren’t any more difficult to diagnose or repair than other vehicles; they’re just different. The Prius transmission is easier to repair than a regular automatic transmission, and often the job can be done with the unit still in the car. Replacing a power inverter is easier than replacing a timing belt, and the hardest thing about replacing a battery pack is finding someone to help you lift it in and out of the car.

The few jobs outlined here are just examples of how simple it can be, but these are just the beginning. If you’re turning away customers with hybrid cars, it’s time to invest in tools and training, because the fleet is growing and there’s money to be made.    ■

‘High-voltage leak detected’

Code P3009 is described as “high-voltage leak detected.” This means the PCM has detected a path from the high-voltage system to chassis ground. This can happen in the motor/generator or in the power inverter, and you wouldn’t tackle those repairs without proper training and information. However, the voltage leak can also occur in the battery pack itself and there’s a simple way to test for this, but it requires erasing the fault codes.
With the codes cleared, turn the power on without pressing the brake pedal. This puts the car into accessory mode, which turns on the 12-volt electrical system. At this point the battery pack relays are open and the high-voltage battery is not connected to anything else on the car.

If code P3009 returns after about two minutes, the problem is in the battery pack itself. If the code returns after putting the car into READY mode, the leak is in the inverter or the motor/generator.

Hybrid system pack fault codes

The Battery Control Module directly monitors the voltage of each module. It also has sensors to monitor the current flow of the whole battery pack and battery pack temperature. Like anything else, a fault code indicates one of two things: a real malfunction or a faulty sensor. Here’s a short list of the battery monitor fault codes.

P0A1F Battery Energy Control Module
P0A7F Hybrid Battery Pack Deterioration
P0A80 Replace Hybrid Battery Pack
P0A82 Hybrid Battery Pack Cooling Fan
P0A84 Hybrid Battery Pack Cooling Fan
P0A85 Hybrid Battery Pack Cooling Fan
P0A95 High Voltage Fuse
P0A9C Hybrid Battery Temperature Sensor “A”
P0A9D Hybrid Battery Temperature Sensor “A” Circuit Low
P0A9E Hybrid Battery Temperature Sensor “A” Circuit High
P0AAC Hybrid Battery Pack Air Temperature Sensor “A” Circuit
P0ABF Hybrid Battery Pack Current Sensor Circuit
P0AC0 Hybrid Battery Pack Current Sensor Circuit Range/Performance
P0AC1 Hybrid Battery Pack Current Sensor Circuit Low
P0AC2 Hybrid Battery Pack Current Sensor Circuit High
P0AFA Hybrid Battery System Voltage Low

Jacques Gordon has worked in the automotive industry for more than 40 years as a service technician, lab technician, trainer and technical writer. His began his writing career writing service manuals at Chilton Book Co. He currently holds ASE Master Technician and L1 certifications and has participated in ASE test writing workshops.

To read more articles by Jacques Gordon, see:

Real World Experience with R1234yf: The New Refrigerant is Finally Here; Are You Ready?

Thermal Imaging: Affordable Technology Lets You See a New LightGasoline: A Designer Product for the Whole World

Chrysler EVAP Performance Codes

Coil-on-Plug Ignition: The Art of COP Misfire Diagnosis

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