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Servicing Mazda Electrical Systems: Starting and Charging Diagnostics

May 1, 2005

While it sounds obvious, the battery is often overlooked when dealing with an electrical problem. Actually, the battery should be more of a maintenance item than a repair issue. I have to think by now all successful import specialist shops are relying on maintenance work to keep their bays profitable. Checking and servicing the battery should be part of that maintenance program. Things like dirty battery cables and a low fluid level should never be a problem on a car that is serviced regularly. Of course, we do see cars that have these problems. When you do, don't hesitate to use it as an opportunity to point out the value of a good maintenance program. It's important to remember that a good battery and charging system is critically important to the operation of the electrical system.

Like everything else in this business, we're seeing some computer-based battery/charging testers that will perform many tests with the push of a button. I'm sure these machines work as advertised and, if you have one, by all means use it. But we know they're not absolutely necessary to perform an accurate diagnosis of the systems we're examining. Follow along as we diagnose the charging and starting system on a Mazda using a DVOM and a two-wire test light.

The first step is to confirm the battery condition. Start by checking the battery with a hydrometer. If the hydrometer test shows a good state of charge, disable the ignition system and crank the starter for about 30 seconds, noting the voltage. It shouldn't drop below 8 volts and return to the 12.5 you should have started with. Reconnect the ignition and start the engine. You're looking for the alternator to increase the voltage by 1.5 to 2 volts; no increase means that system is not charging. If it is, the next step is to put the system under load by turning on electrical accessories like the heater fan, rear defrost and high-beam headlights. At 2,000 rpm, the alternator shouldn't allow voltage to drop below the 12.5 volts you had with the KOEO.

This is also a good time to check for proper operation of not only the charging system warning lamp but also all of lamps. Be sure the battery lamp lights in the KOEO position and goes out when the engine is started. While it's no guarantee the system is charging, it can make the diagnostic process easier if it's not. It also lets you know that the customer would have no warning if it were an intermittent problem. The importance of the other warning lights operating properly is obvious.

For this example, we'll use a 1997 626, but before you do any testing, be sure to refer to your service information. While the strategy of all the systems is similar, execution will differ by model. For example, the Protégé differs in that voltage regulation is controlled by the ECU instead of a regulator in the alternator.

Looking at the 626, if you have no lamp function, unplug the connector at the alternator; the KOEO current should be present at both the S and L terminals. If power isn't available, find out why. On our 626, the white/black wire is the signal wire that tells the system to charge while operating the lamp. The black load wire reports the state of battery charge and should have current at all times. If current isn't present, look at the circuit in the wiring diagram for likely places a problem could occur. It can be as simple as a blown fuse, or as complex as an open wire in a harness, or both, with the chaffed wire causing the fuse failure. Don't overlook bad connections or broken wires at gang plugs connecting the harnesses. If power is available and the lamp isn't lit, ground the black/white wire to the alternator housing to check for a bad bulb. If the lamp now lights, you have an internal problem with the alternator calling for a high-quality rebuilt unit. If there's no voltage at the black wire, you should have seen an overcharge condition (15 or more volts) on your initial test. Reinstall the plug in the alternator and check that you have charge voltage at both terminals with the engine running.

The other side of the coin is when the warning lamp functions as expected, but the system isn't charging as it should. In this case, we know the alternator is making enough power to at least equal the battery voltage and turn off the lamp. But it's either not getting back to the battery, or it's not making enough to keep the battery charged.

The first test is to check voltage at the output or recharge wire at the alternator. On our example, it would be the heavy gauge white and green wire. It should pretty much match the reading at the battery within one-tenth of a volt. If not, there's no point going any further until you find the open in that circuit. Likely suspects would be the fuse links and bad connections at the battery or alternator. Keep in mind that the cars that have found their way to the shop with battery problems have probably been jump-started recently. Nothing will blow fuses faster than reverse polarity.

If you suspect that's the case, check all fuses and links carefully. I suggest using a power probe or similar tool designed for this purpose, with the key and the lights on, looking for current at both sides of the fuse. If there is no voltage where you expect it, head to the underhood fuse link box and check the links for continuity. If battery voltage is present, do a voltage drop test on the recharge wire. Connect the positive lead of the voltmeter to the clean positive terminal of the battery, and the negative lead to the recharge terminal at the alternator. Start the engine and load the system with accessories: heater fan, rear defrost, lights. With the engine at 2,500 rpm, anything more than 0.2 volts should have you looking for bad connections.

This is also a good time to check that the ground side of charging system is in good shape and allowing all the current being produced to find its way back to the battery. Mazda, like many other manufacturers, solid-mounts the alternator to the engine, so grounding problems aren't common. It's not unheard of though for some corrosion at the mounting point to isolate the unit from the engine, resulting in a poor ground, or for bad engine grounds to result in low output. Performing a voltage drop test will confirm a solid ground. Use the same conditions as the test above, but this time the positive lead of the meter is hooked to the negative side of the battery, with the negative lead hooked to the case. Here we're looking for a max of one-tenth of a volt. If you have excessive drop at the alternator, move the lead to a clean spot on the engine to confirm that the engine ground isn't the problem. It's also a good time to check the body ground and rectify any problems that are found.

Now that we have a solid charging system, let's take a look at some of the starter issues we may encounter. No diagnosis can take place on the starting system without confirming battery condition: Be sure the fluid level is topped up and that it's in a good state of charge with clean connections.

Starter complaints will present themselves in a couple of ways, with the most common being, "I turn the key and nothing happens." Of course, that usually isn't the case: Something has indeed happened, but it wasn't what the customer expected. My response to this comment is, "what happened next?" If they drove the car into the shop, they had to do something to get it started. If it's an intermittent problem, this is your best chance to narrow it down. Were the warning lights on the dash lit? Was there a distinct one-time click under the hood when the key was turned to the start position? Did you move the gear selector to confirm you were in the start position? And the most important question of all: Are there aftermarket alarms or self-starter systems on the car?

Other complaints could be slow, labored cranking or an extending cranking period before the engine starts. You might get a gear clash noise complaint, but flywheel problems aren't common with Mazda. For the most part, these conditions are caused by reasons other than the starter, but the customer doesn't know that when presenting the car for repair. That's why they're at your service desk.

We'll use the same 1997 626 as our diagnostic example. Again, using the wiring diagram as our road map, you'll note that the circuit is relatively simple and has proven to be reliable. Turn the key to the start position, and current is fed through the closed starter interrupt relay that is powered by the engine fuse and commanded closed by the OEM security system through the central processing unit.

From the relay, the current passes through the gear position switch on models with automatic transmission, or the clutch switch on manual transmission-equipped cars, to the starter solenoid. If you're faced with the "I turn the key and nothing happens" complaint, the most likely suspect is the starter contacts in the unit. This can be confirmed by the heavy clicking sound coming from the starter when the key is in the start position. Many times, successive clicking of the key to the start position will eventually burn through the corrosive surface on the contacts, and the starter will operate. This problem occurs mostly on cool, damp mornings, so if the complaint involves a no start in the morning but normal operation in the afternoon, I would also suspect the contacts. While the contacts are available, inexpensive and easy to install, I prefer to install a high-quality rebuilt unit that protects both my shop and the customer with a strong warranty.

If your diagnostic process shows no current getting to the start signal terminal, you'll have to look further. Locate the starter cut relay in the underhood fuse box. Have an assistant turn the key while you confirm that the relay closes. If it doesn't, check that current and ground are present at the coil terminals of the relay. If it is, you will need a new relay. If not, use your wiring diagram to trace out the problem. If it's the ground that's missing, there may be a problem with the OEM anti-theft system. It would take another article to go over the diagnostics of that system. But again, check all fuses, close the hood and all the doors, and try locking and unlocking the doors with the key. If there's still no ground, you'll have to get into checking the central processing unit.

From the switch side of relay, we can confirm that the signal is coming from the ignition switch and the circuit to the starter. With the relay removed, the terminal going to the starter should show ground, while the switch terminal should show nothing until the key is in the start position, when battery voltage should be present.

I mentioned earlier that it's important to know if the car is equipped with an aftermarket alarm or remote start. If you don't get a signal from the ignition switch, and the car is equipped with one of these accessories, take a hard look at how it was installed.

Not all of the folks who install these devices give the wiring the consideration they should. It doesn't always stand the test of time, resulting in open circuits. If your shop is like ours, we've removed far more of these devices then we've installed. Keep in mind there is always the possibility that your customer purchased the car used and isn't even aware the accessory is there until it becomes a problem.

One of the problems that seem to stump experienced as well as new techs is the slow crank problem. After confirming that the battery is good and strong, start with some simple tests. With a volt- meter hooked to the battery, engage the starter making note of the voltage while cranking. You're looking for about 9 volts while cranking. If it's not pulling the voltage down, it's time to do some voltage drop tests. Using the same procedure that was described previously, check that there is no voltage drop in the battery cable or the ground side of the system.

If it pulled the voltage down lower than expected, suspect excessive draw in the starter or a mechanical condition making the engine difficult to turn over; neither of these conditions are common. The mechanical drag can be confirmed by manually turning the engine with the crank bolt. There's no hard spec on the torque required to turn the engine over, but if it's tight enough to cause a cranking problem, you'll know it. While excessive starter draw can be confirmed with an amp draw test, if the other tests were good, it's a safe bet the starter is the problem and should be replaced with a high-quality rebuilt unit.

I hope you found this article helpful. My goal was to give some insight into the charging and starting system on a Mazda and show it's not the amount of equipment used that makes a good diagnosis and repair, as much as a good strategy and a well-informed import car tech.


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