High voltage hybrids have been out close to two decades. More recently, 48-volt micro hybrid electric vehicles have been introduced in Europe and will soon be spreading to American roadways starting with select 2019 Dodge, Jeep and Mercedes models.
All this greatly increases your chances of having to work on hybrids and EVs beyond the realm of preventative maintenance. To prepare you for today’s higher voltage hybrids as well as tomorrow’s lower voltage 48-volt systems, we’ll go over some common hybrid DTCs to help you diagnose faster by understanding how they work and why they set.
P0A0D – High voltage interlock circuit voltage high
The title of this common DTC is a bit misleading. The circuit that sets the DTC itself is NOT a high voltage circuit but rather a 12-volt circuit that is a watchdog for high-voltage components (Figure 1). On GM 2-mode HEVs for example, if you remove the hard plastic cover that hides the inverter and DC-DC converter assembly a shorting bar in that plastic cover is now pulled from a connector in the HV interlock circuit. A similar arrangement is on Toyota inverter cover plates (Figure 2). A DTC P0A0D then sets and the high voltage contactors in the battery pack open (if they were closed) or won’t close if you then try to power up the vehicle. On Fords (Figure 3), this circuit will be attached to the major orange high voltage cables to insure those cables are fully seated/latched. On many hybrids, simply extending the high voltage battery pack’s service disconnect plug (Figure 4) prior to unlatching it will remove a shorting bar in the service plug from the terminals in this circuit. The whole point of this circuit is for safety.
P0AA6 – Hybrid battery voltage system isolation fault
Battery packs are subject to leakage DTCs as are motor generators, HV electric AC compressors and high voltage cables. Full-voltage (over 60 volts) HEVs and EVs connect both of their HV battery pack’s cables directly to the inverter. The negative DC HV cable does NOT connect directly to chassis ground. However, if you have ever connected a DMM set to DC between chassis ground and either of the HV battery pack’s positive or negative cables you will read half of the HV battery pack’s voltage on Toyotas. On Fords, you’ll see something curious; a rhythmic sweeping of this voltage moving from 0 volts up to about 70 percent of the HV battery pack’s total voltage. This sweeping action takes just a couple of seconds. This “diagnostic” high-voltage circuit carries a harmless low current – about 2 mA. It is there to inform the vehicle’s electronics of the even the smallest amount of high voltage leakage. Similar in design intent to a bathroom/kitchen’s GFI (Ground Fault Interrupt) they cause the disconnection of high voltage power for safety’s sake. The down side is a no start condition will occur on HEVs that use their MGs for starting the gas engine. Isolation fault detection use high ohm (typically around 150K ohms) resistors in parallel between the high voltage circuit and chassis ground (Figure 5).
P0A80 – Battery performance
While the first two DTCs may not appear on the newer 48-volt micro hybrids this battery performance DTC will most likely be applicable to just about any hybrid or EV on the road regardless of voltage levels. The P0A80 is a generic DTC and the reason a lot of battery packs get replaced. This DTC basically says the hybrid battery pack “smart” module has detected a variation exceeding 0.3 volts between pairs of battery modules. Battery modules in the case of the older (and popular) NiMH battery packs are either cylindrical (appearing like large D-cell flashlight batteries) or prismatic (flat rectangular) groups of six 1.2-volt cells in series equaling 7.2 volts. Two NiMH battery modules are then wired in series to comprise a battery block (Figure 6).
The battery blocks are then wired in series within the pack to comprise the HV battery pack’s total voltage. The battery control module/smart battery unit monitors the internal resistance, temperature, voltage and current draw of the total battery and its individual blocks. If the blocks are not nearly identical in voltage under various conditions, the module with flag this DTC. However, diagnostic charts for this DTC can be a bit confusing (Figure 7). The charts instructs techs to use a scan tool to monitor the voltages between the various combinations of blocks. You’re supposed to replace either the battery pack or the battery control module depending on the outcome of the battery block voltage comparisons. The key word is “ALL” in the chart when the question is posed regarding “are all the battery block voltages greater than 0.3 volts from each other?” Toyota makes this distinction clearer than Nissan by stating that a common symptom of a faulty battery control module (battery smart unit) is ALL of the battery blocks being 0.3 volts different than each other.
48 volts? Again?
Didn’t the industry already try that once? Forty-two-volt dual voltage systems were designed and ready to implement in the late 1990s. The 42-volt systems did NOT make it from the engineering labs of OEMs and into consumers’ driveways outside of the few exceptions of GM’s early BAS (Belt Alternator Starter) blue cable models and the PHT (Parallel Hybrid Truck). Neither the 42-volt BAS or PHT technology had the latest Li-Ion high output/low-weight battery packs that today’s HEVs and EVs are equipped with. Inverters and DC-DC converters used IGBT (Insulated Gate Bipolar Transistor) technology that was state of the art then. A new technology referred to as the “Viper inverter power switch” by Tier 1 OEM supplier Delphi Technologies allows for new inverters and converters to be 40 percent lighter and 30 percent smaller. This leads to a 25 percent higher power density increase. The Viper power inverter switch also does away with wire bonds and tedious connections, which can lead to quality and reliability issues.
Unlike more complex and higher voltage HEVs/EVs, a 48-volt system will not propel the vehicle around town without the gas engine contributing power. Then why bother? Increasing voltage for high wattage accessories and functions is fueled by a simple electrical principle called “Watt’s Law” (Figure 8). The higher the voltage, the lower the amperage required for a given electrical work requirements (watts). While higher voltage systems are typically required for propelling the vehicle without the I.C.E., the extra voltage that 48-volt systems afford have a fair amount of other benefits. A 48-volt system is quite adept, being able to spool up an electric super-charger to launch the vehicle faster and smoother, eliminating turbo lag. Other heavy electrical (high wattage) load such as A/C compressors and electric power steering motors will run more efficiently on 48 volts as well.
48-volt system safety and simplicity
GM advised technicians back in their small niche 42-volt era (BAS/PHT) to practice similar safety precautions they were in the habit of doing on higher voltage systems during the service of the high-voltage side of the vehicle. OSHA regulations however, are laxer with voltages under the 50-60 volt region that borders the realm of injurious to lethal. This eliminates the need for heavier and more expensive circuits that lead to DTCs such as P0A0D and P0AA6. That means 48-volt and 12-volt systems can both share a chassis ground (Figure 9).
When will we see 48 volts?
Forty-eight-volt vehicles have already been appearing in Europe in fair numbers due to the higher price of fuel there. As for models made in/imported into the USA, Mercedes has launched 48-volt system in their CLS 450 model (Figure 10) for American roads this year. In addition, select Dodge Ram 5.7 liter V-8 Hemi, Dodge Ram 3.6 liter V-6 and Jeep Wrangler 3.6 liter V-6 models for 2019 have adopted a belt driven 48-volt motor generator system called E-Torque.
Dodge/Jeep E-Torque 48-volt system explained
The E-Torque system uses two major serviceable assemblies each containing non-serviceable main subassemblies/components.
- Battery Pack – PPU (Power Pack Unit)
HV Battery, HV Battery Control Module and DC-DC Converter
Dodge’s 48-volt Li-Ion battery pack contains a BPCM (Battery Pack Control Module) that is an integral part of the complete PPU (Power Pack Unit, Figure 11). The PPU’s Li-Ion battery pack is an air-cooled unit containing 12 4-volt Li-Ion cells. The BPCM monitors for current, temperature, voltage and internal resistance of the pack the same as any HEV/EV’s battery control module. The BPCM also controls the charging and discharging of the battery pack. The BPCM’s HV battery self-diagnostics include SoC (State of Charge) and SoH (State of Health). SoH is based on the rise in calculated internal resistance and decrease in capacity. Battery end of life is generally defined as a 20 percent decrease in the 48-volt battery system capacity or 25 percent power degradation. The unit contains a DC-DC converter, which is, of course, any hybrid vehicle’s solid-state version of a conventional 12-volt alternator. The BPCM communicates on and manages a special CAN bus called a CAN-ePT data network. The CAN-ePT is a private bus network used only in the e-Torque system with e-Torque components.
- Belt driven MGU (Motor Generator Unit)
Motor/Generator, Inverter and Main Hybrid ECU
The MGU mounts on the front of the engine (Figure 12) and contains the HCP (Hybrid Control Processor) which is the major smarts for the entire e-Torque system. The HCP serves as an electronic controller for the E-Torque system as well as an inverter module to change the MGU’s internal 3-phase AC to 48 volts of DC power. The HCP commands the PPU to close the HV battery pack’s contacts via a bus message. The HCP also serves the important job of sending the PPU a message to go into a cell balancing mode when the BPCM indicates there is an imbalance. The MGU also serves as the starter motor to crank the engine as well as the generator for the vehicle. E-Torque systems also utilize a stop/start strategy that interfaces with several other modules on the vehicle such as the HVAC, ABS and TCM. In addition to electrical generation and gas engine stop/start duties the MGU handles regen braking and engine low end torque boost with 130 ft. lbs. of additional torque.
HCP Flashing Precaution: BPCM Flashing Precaution: The ignition state needs to be transitioned to OFF for at least 30 seconds and then transitioned to RUN prior to flashing the BPCM. This allows the PPU’s contactors to be commanded open. If the ignition state is cycled too fast, a precondition warning may occur which could prevent the flash programming procedure from completing. |
48-volt future – big or small?
According to the EPA, a fleet of 11 million 48-volt mild hybrids would benefit consumers and increase the nation’s air quality by saving over 4 billion gallons of fuel over the life of those vehicles. That’s a very good thing no matter how you state it. Will we see 11 million new 48-volt micro hybrids or will the American fleet hit some other number...lower or higher? Mary Gustanski, senior vice president and chief technology officer for Delphi Technologies gave some interesting insights into that question as she predicted some directions where electrification is likely to be heading while speaking at the 2018 AAPEX show in Las Vegas. Significantly lower costs for 48-volt systems are a big plus but higher voltage system prices have started coming down. Adding into that mix are the variables of governmental policies regarding required MPG increases/relaxations along with EPA restrictions on PM (Particulate Matter) and NOx (diesel emissions) for the diesel option some OEMs take. This leads us to the opinion that the only thing we can really bank on is more electrification and continuing changes in technologies. To that end Motor Age will be keeping you informed and ready for whatever new technology comes into your service bay!