Battery and charging technology, along with ever-expanding on-board electronics, continue to evolve and increase in complexity. This article by noted mobile diagnostic technician Edwin Hazzard offers insights and tips for checking battery and charging system health and diagnosing related issues.
When you talk about diagnostics in the automotive industry, the first thing that usually comes to mind is a computer problem like an engine system, anti-lock brake system or maybe even a body control issue.
Diagnostic issues can be caused by a multitude of different problems ranging from control modules, solenoids, sensors or even wiring and or data malfunctions. This article focuses on an area of the diagnostic puzzle that is often overlooked in our diagnostic thought process... the electrical system, predominately the starting, charging and battery systems.
These three systems can have their own set of diagnostic issues, but nevertheless need to be diagnosed correctly. Sometimes it’s in one of these three component areas that is causing your computer system to not work properly and it just might not be a computer system problem after all but an underlying problem.
In my last article (December 2017) I talked about how the battery is the heart of the electrical system and that’s where the vehicle’s so-called lifeline starts. When performing an electrical system diagnostic, always start at the battery.
Years ago the automotive battery was relatively simple and not too sophisticated as compared to current battery technology (see “OEM battery trends” article on page 18). When we tested batteries from years back, many of us would use the “toaster” type testers which would essentially draw a fixed current of anywhere of 100 amps to 300 amps. This just wasn’t a very accurate test but would kind of give us an idea on the condition of the battery… sort of.
As you know, when performing a battery test, the battery has to be able to accept a full charge so a proper test can be performed. Today’s modern day battery testers will test the battery using the capacitance type test, where the tester injects a very small AC voltage (E) of known amplitude and frequency into the battery.
In this article I’m not going to go into the specifics of battery testing techniques, but will concentrate on battery diagnostic problems.
When we receive a customer concern that the battery is dead and the engine won’t start, a couple of things need to be performed.
First off, the battery needs to be fully charged and then needs to be tested. This will tell the technician the current condition that the battery is in. If the battery won’t hold a charge let alone accept a charge, then a battery replacement is in order.
An important step in battery testing is to test the battery without the battery cables connected. Having the cables of the vehicle still hooked up to the battery will give you an inaccurate reading as you are testing the extra resistance of the components in the vehicle such as the battery cables, starter, etc. You want to isolate the battery separately from the vehicle and that also includes batteries that are used in series.
Another diagnostic tip is to make sure that the battery doesn’t have a lot of corrosion on the surface. That “Chia Pet” buildup will play a part in your battery diagnostics in that it will add unwanted resistance to your test results and possibly give you a false reading which could potentially lead to premature battery replacement. Clean the surface well with a good battery cleaner before you recharge the battery and before you test it.
Let’s fast forward to today’s modern day battery systems and battery management. One of the newer features in some of the vehicles we see today is the “start-stop” system. The start-stop system has been added to the vehicle to primarily increase fuel mileage. The engine will shut off when the vehicle has come to a complete stop as if the engine has stalled. When the driver takes their foot off of the brake pedal, the engine will restart.
This is monitored by the vehicle’s body computer to watch the system voltage. Once the voltage has dropped below a predetermined specification due to other system inputs like the HVAC blower fan, headlights and various other electrical demands, the engine will restart and resume normal operation.
For example, on a 2017 Chevrolet Cruze the battery management system relies on a sensor to constantly monitor the condition of the battery based on the input that’s received by the vehicle’s charging system and the loads placed on the electrical system. The battery current sensor is a sensor that acts just like an amp clamp. The battery cable is routed through the sensor itself. The battery current sensor is a serviceable component that is connected to the negative battery cable at the battery. The battery current sensor is a three-wire Hall affect current sensor.
The battery current sensor monitors the battery current. It directly inputs to the BCM. It creates a 5 volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100%. Normal duty cycle is between 5-95%. Between 0–5% and 95–100% are for diagnostic purposes.
Once you have determined that the battery is operating as designed, then the next step in the diagnostic process involves the charging system. The charging system of the vehicle is just as important as the battery itself as this is the part of the electrical system that keeps the battery in check.
The charging system helps maintain the battery state of charge by regulating how, when and for how long the battery needs to be replenished. When beginning your charging system diagnosis, the very first thing you should do is to perform a good visual inspection. Performing a good visual inspection might alert you of a potential problem, thus minimizing the risk of a misstep in your diagnosis.
One thing to look at is the belt that allows the alternator or generator to spin. Is the belt cracked, frayed or loose? In what condition is the pulley or pulleys that the belt rides on? Don’t forget about the tensioner and pulley. Is it in good working condition? Look for any signs of oil or coolant on the belt which could allow the belt to slip on the pulleys and possibly deteriorate the belt and shorten its life span.
Another area to check would be the electrical connections to the alternator. Give the connections a tug to see if they could be loose. If the connection is loose, it’s not going to operate properly.
In order to determine if the alternator or generator is electrically charging correctly, you need to know what the specs are for the vehicle you are working on. These can be obtained through the vehicle manufacturer or a service information system.
On our demonstration vehicle, the 2017 Chevrolet Cruze, the charging system is monitored and controlled by the vehicle’s ECM. The engine control module (ECM) uses the generator turn ON control circuit to control the load of the generator on the engine. A high side driver in the ECM applies a duty cycled voltage to the voltage regulator.
The duty cycle controls the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the generator turn ON control circuit. The ECM should detect low voltage on the generator turn-on control circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect high voltage when the duty cycle voltage is commanded high, and a low voltage when the duty cycle voltage is commanded low on the generator turn-on control circuit.
Diagnosing the charging system on this vehicle is essentially done with the use of a scan tool. If there is a problem it will usually generate a diagnostic trouble code. However, if you want to perform an alternator output test you can do so by using a handheld electronic electrical system tester like the one in Figure 2.
On newer vehicles, it’s more difficult to perform this test, as the battery charging tolerances are different due to the electrical loads placed on the vehicle are a lot less. Some of this is due to more LED lighting and other less-power-robbing components.
To manually check alternator output using an electronic handheld tester, hook your two clamps on each post of the battery and your inductive clamp around the positive cable going to the alternator. Most testers will guide you through the test and point out if the unit has passed or failed.
Remember, in order to obtain an accurate test, the battery must be able to operate at full capacity. If for some reason you don’t have access to a handheld tester, you can use your DVOM and an amp clamp suitable to handle the higher amperage required. Some amp clamps like the one shown in Figure 8 have a built-in DVOM.
Zero out the meter and place the amp clamp around the positive cable of the alternator. Set your meter reading to the amps scale. Start the engine and make sure all electrical load like headlights, wipers, blower fan, etc., are turned off. Raise the rpms to about 2,000 and observe the status of the meter. Hold for a minute to let the system stabilize. Next, return the engine to idle. Now, turn on as many electrical loads as you can and repeat the steps that you performed when there wasn’t any load on the system. Compare the two readings. You should see a slight increase depending on the state of charge of the battery.
This is a crude test but it will give you an idea if the alternator is in fact working and how well it is working. Like I stated earlier, today’s vehicle electrical management systems have notably more control over system charging than just the alternator itself.
Starting system diagnosis
At this point, we move on to our starting system diagnosis. One of the few things besides normal wear and tear that will shorten the life of a starter is the lack of proper voltage going to the starter. Issues can be caused by either a loose connection or excessive resistance in the circuit. Battery cables that have a high resistance can dramatically reduce the available amount of amperage that the starter needs to properly start the engine.
One important test in starter diagnostics is to perform a voltage drop test on the battery cables, both at the positive and the ground side of the starter. You need to make sure that the proper voltage required and the starter ground side have good clean connections. Any circuit that has excessive resistance will not properly operate the component on that circuit.
Testing a starter motor for the correct amperage draw can be done in a couple of ways. One approach involves using an electrical system tester like the one shown in this article or by using a standard DVOM and a high amps current clamp. When using a meter and a clamp you can set your meter to the voltage scale and hook your amp clamp to one the battery cables.
Disable the fuel or ignition so the engine will not start during the test. Crank the engine as you observe the tester’s ammeter and voltmeter. Never crank the engine for more than 15 seconds and allow the starter to cool for two minutes between cranks.
Slow cranking and high current draw typically indicate worn bearings or bushings inside the starter. Worn bushings result in an off-center armature. This can result in poling and can throw off the alignment of the starter’s magnetic fields. Observe the voltage and the amperage at the same time. The voltage should remain at or above specifications while cranking the engine.
High current draw and low cranking speed indicate a faulty starter or possible engine problems. Low cranking speed and low current draw indicate excessive resistance in the starter circuit.
Always check specifications; the bigger the engine the higher the current draw. Typical readings for a four cylinder engine is 150 amps, six cylinder is 200 amps and eight cylinder is 250 amps. Remember, these specs are only approximate. You need to consult your service information system for the proper spec for the vehicle you are working on. Also, remember that any of these testing procedures are null and void if your battery isn’t working properly.
Automotive electrical diagnostics play a very important role in today’s increasingly sophisticated electronics-laden vehicles. There are miles of wiring in these vehicles, and the electrical system has to be in tip-top shape to be able to power these systems for proper working order.
Manufacturers such as Clore Automotive, Midtronics and Interstate Batteries all have contributed to the electrical diagnostics part of our industry. The technologies that have changed over the years have given us some pretty tough challenges, including new battery technology, such as AGM type batteries or valve regulated lead acid type batteries, deep cycle batteries and battery systems used in hybrid vehicles.
There are three major types of batteries that companies use or are considering for use in hybrid cars: lead-acid, nickel-metal hydride (NiMH) and lithium-ion (Li-ion). Electrical system testers have evolved as well. The testers available for today’s modern vehicles are getting increasingly more accurate as battery technology, charging systems and starting systems become more complex. Today’s testers not only measure voltage and amperage, but use impedance and or conductance testing as well.
As many of you have noticed in recent years, replacing a standard car battery isn’t as simple as it once was. Sometimes you have to remove multiple panels just to gain access to these batteries. To add insult to injury, some of these vehicles require that the batteries are registered with a scan tool for the electrical system to work properly!
For example, on a BMW 320i xDrive: If the vehicle has the energy management system like IBS or power module, then a battery registration is needed. The reason a battery registration is needed is that the vehicle’s electrical system is informed about vehicle data characteristic data such as type, size, age and current power capacity.
If performance drops below a defined minimum, the check control message will alert the driver that a battery replacement is needed. When replacing the battery, a battery registration must be performed so the control module will have updated information. This will allow the check control message to go out.
Also, if retrofitting with a bigger, more powerful battery in place of an OEM spec battery, the new battery information will need to be registered as well. When the battery is registered, the stored energy history is deleted. If the battery is not registered, this may cause the root cause to return.
That is why staying updated on your training and the new technologies that will be entering your service bays in the not so distant future is mission-critical for properly servicing your customers.
As a close friend of mine would say, “Either update or evaporate.” ■
Edwin Hazzard owns South East Mobile Tech in Charleston, S.C., which is a mobile diagnostic and programming service providing technical service to many automotive and body repair shops. He has 35 years experience in the automotive industry. He currently is an automotive trainer, a board member of TST (Technician Service Training), a member of the MDG (Mobile Diagnostic Group), a member of the Professional Tool and Equipment advisory board for Pten magazine, a committee member of Nastaf, and is a beta tester for multiple tool makers.