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ELECTRICAL CIRCUIT SHORTS PARASITIC DRAW BATTERY-CAR-REPAIR-HOUSTON,TX

Friday, February 1st, 2008

Exterminating Electrical Parasites


By Glen Beanard, technical contributorAny electrical circuit that is wired “hot at all times” has the potential to become a parasite to the battery. There are some wanted parasites on the vehicle that are necessary to have, and some that are not. We’re going to find out how to “fingerprint” and track down the unwanted ones systematically.A parasitic draw on the battery means that, while the key is in the off position, something is pulling amperage from the battery. Like a glass of water that is slowly sipped on, it will run dry. The symptoms of a parasitic draw, or the customer complaints, can vary depending on the situation. Not every vehicle with a parasitic draw will come towed in with a dead battery. In fact, some may not even require jump starting to bring them in. It just depends on how low the battery is allowed to get before the next start. Intermittent electrical issues like:

  • gauges sweeping or inoperative at start up;
  • memory seats, mirrors and column not self adjusting;
  • radio presets disappearing; and
  • rough engine idle and harsh transmission shifting after first start-up in the morning are all possible symptoms of a parasitic draw on the battery. Any of those issues, and more, may have “healed” themselves by the time the customer brings it to your shop to check them out.

When the customer experiences one of these issues that could be caused by a weak battery, possibly from a draw, it can be helpful to perform a full body code scan. Clues can be found in various modules such as a P1000 in the PCM, or “battery voltage low” codes found in air bag, ABS, instrument cluster and various body controller modules. A vehicle with a battery voltage low code stored in any module should be tested for a parasitic draw.

Prepping the Patient
Getting a vehicle ready for a draw test involves a tad bit more than just hooking up an ammeter. With today’s vehicles, various modules (and lights) are awakened by simply operating a door handle. Since the awakening of modules (and lights) will suddenly cause an expected electrical draw, how are you going to access the inside of the vehicle after you determine there is an unwanted draw in the passenger area? Opening a car door at that point will bury the draw test results in a flood of amperage flow to other circuits. Before beginning a parasitic draw test, remove the key from the ignition and open all doors including the back hatch if equipped. Then, defeat the door ajar switches. For many modern vehicles, such as this 2005 Ford Explorer, this is done simply by using a screwdriver to artificially close the latches. See Photo 1.

For others, defeating the door ajar switches may mean removal of the switches from the door jam or inserting something in the door jam that artificially depresses the switch. Don’t forget to do the same for hood switches on some vehicles as well. Removing the key and defeating all door switches with the doors open will give the body control modules the illusion that you have exited the vehicle, yet you will still have full access to the interior of the vehicle for later pinpoint testing.

Next, set your ammeter up at the easiest to access (and cleanest) battery terminal. Though you could just snatch the cable off and put your ammeter in-line, I suggest some care is taken at this point. With most top post batteries anyway, it is possible to set your ammeter up without breaking the circuit with just a few simple and quick steps.

Step 1: Using a pointed lead for one tip and a gator clamp for the other tip, connect the gator clip to the cable and dig the pointed end into the top of the battery post for future foot holding. Be sure the leads are properly connected to the DVOM and that the DVOM is set to the ammeter setting. See Photo 2.

Step 2: Lift the battery cable up, the ammeter will be completing the circuit if the cable loses contact with the post. Then slide the cable over to the pointed probe that is on the top of the post. Push the eye of the battery cable down so that it is in contact with the battery post. See Photo 3.

Step 3: Lift the pointed probe over the battery cable’s eye, and back to the post outside of the eye. See Photo 4.

Step 4: Pull the battery cable away from the post and drag the pointed probe back to the mounting dent that you made in the top of the battery post. A few twists of the probe into the soft lead post, and the probe will stand up and hold itself in place for testing. See Photo 5.

For some vehicles, it might be easier to use a jumper pack set up for supplemental power while hooking up the ammeter, especially for side post batteries. For others, this little bunny hop of the test lead may be faster. But the idea here is to maintain things like radio (especially security radios), clock settings, power window settings (rather important to do so on some makes and models), and aftermarket alarm systems to reduce the unwanted stress of having to deal with a customer screaming about lost settings.

Ever have an alarm system lock out the starter and find out that the customer has no key fob for it? That’s real fun. Granted, with the nature of the problem that we might be looking for next, we just might wipe some of that stuff out during testing anyway. But remember, we don’t know for sure if we have a draw yet. So at this point, let’s not make more work for ourselves… there is still a chance we’ll find no draw after all. It’s bad enough to lose some settings when we have to, it’s worse when we later find out we didn’t have to at all.

OK, so now the ammeter is set up and we have a value showing on the meter. Wow, the meter is showing 0.59 amps. See Photo 6.

That’s a pretty hefty draw there. Is that a problem? Actually, it’s too soon to tell. Remember all that door ajar switch defeating we did a little bit ago? Why did we do that? There are some body modules on this vehicle that haven’t gone to “sleep” yet. On any given vehicle there can be a handful of modules like BCM (GEM), vehicle security, lighting control and so on that will stay awake for as long as 45 minutes after the last door handle, door switch or key-in-sense switch has been tripped. So, we need to wait about an hour before reading the ammeter. Leave the ammeter hooked up, just turn off the power switch on the ammeter and go do something else for an hour. We’ll come back to that later, just remember where we left off.

Fingerprints of a Suspect
Some techs will argue that you can use a bulb-type test light for draw testing, and some will argue that you cannot do it on today’s cars. I’m not going to sit here and tell anyone that they can’t possibly test for a draw with a test light, because I myself have done it. On the other hand, I’m not going to endorse the use of a test light for draw testing either. Even though I’m guilty of it, I will say that draw testing with a test light is unwise. If a draw is small enough, it may be missed with a test light. If it’s large enough to see with a test light, just how large is it? It’s unwise to attempt to use a test light largely because it doesn’t allow you to see the parasite’s “fingerprint.”

What I mean by a fingerprint is that different items have a signature amount of amperage that they will draw. For example, you might measure a parasitic draw of 0.15 amps at the battery. Everything that is wired hot at all times is suspect of a draw, but there might only be one item on the vehicle that will draw that exact signature 0.15 amps and also wired hot at all times. In theory, if there were a published spec you could look at of what each item draws, you could probably go straight to it off of that. But as it is, you have to hunt for it… but at least you know that you are hunting for a 0.15-amp draw. A test light hides that fingerprint from you. With a test light, what is a 0.34-amp brightness? Or a 0.25-amp brightness? How bright is “a little bright”? Have you ever had a draw go away after you’re getting close to it during testing?

If you know the signature amperage, and you’ve narrowed the suspect down, you might be able to prove to yourself what the draw is by manually stimulating a suspect module to see if its signature draw matches what you were hunting for before it “healed” itself. You can’t do that accurately with a test light.

Let’s Get Hands-On
Let’s go back and check that 2005 Explorer. After a suitable time out period, the amperage draw has reduced to 0.20 amps. See Photo 7.

That’s better; some modules have gone to sleep, but still something is sneaking electron sips from the battery and we have its fingerprint. The next step is to isolate the circuit where the offender is hiding. A great way to do this is remove and reinsert underhood fuses one by one while monitoring the draw amperage. However, keep in mind, that while you do this, you will often wake up modules when you reinsert
the fuse. In which case, you will need to wait until such a module goes back to sleep before continuing to the next fuse. When you pull the right fuse, the draw will stop on the ammeter. In the case of this Explorer, it was a 60-amp fuse in the underhood fuse panel — fuse 1. See Photos 8 and 9.

When fuse 1 was pulled, the current dropped to zero. Looking at the fuse explanation chart (Photo 10) for the under hood fuse panel (panel number 1), shows fuse number 1 (1.1) to supply power for fuses 1, 2, 3 and 5 in the interior fuse panel (panel number 2).

Pulling these fuses one at a time in the interior fuse panel hit pay dirt when fuse 3 was removed, the current draw dropped to (nearly) zero once again. See Photo 11.

Looking at the fuse chart for the interior fuse panel found three suspects listed. See Photo 12.

The draw was proven to be in the direction of the audio unit (radio), amplifier or the DVD player (if equipped). The DVD player was quickly eliminated from the suspects list, due to the fact that this vehicle didn’t have one. The amplifier is behind the trim panel to the right of the cargo area. Not hard to get to, but the radio slides out of these easier. So, the radio was removed and unplugged to see if the draw went away. See Photo 13.

With the radio unplugged, the ammeter was inspected again for the results. The draw was still there. Only one suspect module left now. Time to go prove it.

With the amplifier disconnected (still shown as connected in Photo 14), the amperage dropped instantly.

The cause of this draw was that the amplifier was not going to sleep. A new amplifier fixed this vehicle. Let’s try another one.

This is a 2005 Ranger 3.0L. At first, battery draw was 0.34 amps. See Photo 15.

After only a few minutes, the draw dropped to the guilty item’s signature draw of 0.14 amps. See Photo 16.

Pulling underhood fuses found that the draw disappeared when fuse 5 (50A) was removed. See Photo 17.

The charts show that fuse to power the “Smart Junction Box” (SJB), which is the interior fuse panel. An SJB is not only a fuse panel, it is also a GEM module (BCM) combined into one unit. This 50A fuse may power a laundry list of items, and the underhood chart is not much help this time since it only says the SJB. So, it’s off to the power distribution charts to see what is powered by that fuse.

A quick look shows that fuses 17, 11 and 12 in the SJB are what that fuse powers. Fuse 17 is for the flasher, 11 is a power supply for the SJB’s logic circuitry and fuse 12 is for the subwoofer amplifier. The SJB was accessed by removing the passenger side kick panel. See Photo 18.

The removal and installation of the SJB’s fuse will awaken the supposedly sleeping module. So, the flasher fuse and the amplifier fuses were pulled. The draw remained. Pulling fuse 11 for the SJB’s logic circuitry dropped the ammeter to zero.

For this model, the SJB had to be programmed. Using the IDS, the configuration data was removed from the old module and loaded into the new module after its installation and the current draw problem was solved. I hope that you enjoyed the information, and have the opportunity to profit from it soon.

Auto Engine Starting-Charging System Problems-Diagnosis -Repair-Alternator,Car Battery,Starter,Engine No Start issues-Houston,Tx

Saturday, November 24th, 2007

STARTING/CHARGING
SYSTEM DIAGNOSIS





Fixing Faults the First Time Eliminates Comebacks & Returnsby Larry Carley, Technical Editor

How many starters and alternators are replaced unnecessarily every year because of misdiagnosis? Nobody knows for sure, but suppliers of both new and remanufactured rotating electrical parts tell us more than half of their warranty returns have “no fault found” when the parts are examined. Many of these returns are from DIYers who lack diagnostic know-how, but some are from professional technicians who apparently lack the same skills.The point we want to stress here is the importance of diagnosing starting and charging problems before any parts are replaced. If you correctly perform the diagnosis, you’ll fix the fault the first time and won’t have to worry about comebacks, returns or your reputation. You’ll also save your customers money and yourself the hassle of trying to fix the same problem again.IT ALL STARTS WITH THE BATTERY
Let’s look at a typical no-start scenario where the engine fails to crank when the motorist tries to start his car. The first thing that usually needs to be determined is whether or not a rundown battery is the reason for the engine not cranking. Starters pull a lot of amps when they crank an engine, and if the battery is low, there may not be enough current available for the starter to overcome the compression, spring pressure and friction within the engine. If the starter cranks normally with a jump-start, though, you can rule out a starter problem right away. The next thing to investigate would be the battery.Did the battery run down because the motorist left his lights on? Has the car been sitting a long time? Is it only used infrequently for short trips? Is the charging system putting out enough amps to keep the battery fully charged? Is there a higher-than-normal key-off current drain on the battery that’s running it down? Is the battery no good?
These are all concerns that can be easily answered by asking the vehicle owner a few questions and performing a few simple tests. If the motorist did not leave his lights on, and the vehicle has been driven daily for at least 20 minutes or more, chances are the car has a charging problem, a bad battery, or loose or corroded battery cable connections.A visual inspection of the battery connections might reveal something if you see signs of corrosion or the cable clamps are loose or damaged. The battery’s state of charge can be tested with a voltmeter. A fully charged battery should read 12.6 volts. Less than 12.4 volts means it’s low and needs to be recharged.The charging voltage can be checked at the battery with the engine idling. Most charging systems will put out 13.5 to 14.5 volts at idle, depending on the temperature and the battery’s level of charge. Less than 13.5 volts would indicate a charging problem.If the charging system is putting out normal voltage, the battery should then be load tested or checked with an electronic conductance tester to determine if it’s good or bad (Note: A traditional load tester won’t give accurate test results unless the battery is first recharged. This isn’t the case with conductance testers because the test results do not depend on the battery’s level of charge.) Average battery life is only about four to five years at best, and can be as little as three years in a hot climate.If the battery tests bad, the vehicle obviously needs a new battery. Replacement batteries should always have the same or higher cold cranking amp (CCA) rating as the original, and be fully charged before they are installed in a vehicle. And don’t forget to attach a backup power supply before disconnecting the old battery on cars where loss of keep alive memory data can cause problems. But what if the battery tests good and the charging system is working normally? Then what? The next check would be to look for a higher-than-normal key-off current drain.NORMAL AND ABNORMAL CURRENT DRAIN
When the key is turned off, the electrical load on the battery doesn’t stop. There is always a small load on the battery to maintain the “keep alive” memories in the powertrain control module (PCM) and other modules. Many modules have internal timers that either turn off the module to put it into a “sleep mode,” or power down the module to a “standby mode” after a certain length of time when the key is turned off. Some of these modules power down in steps and time out at different rates.
As a rule, the key-off current drain on most late-model vehicles should be less than 50 milliamps (mA), one hour after the vehicle has been shut off and left undisturbed.The key-off drain can be measured with a milliamp amp probe or an ammeter. A clamp-on amp probe is the better choice here because you don’t have to disconnect a battery cable as you would if you use an ammeter. Disconnecting the battery on many late-model cars without first connecting a battery backup to maintain the keep alive module memories can create additional problems. Any disruption in power, even for a split second, can cause the PCM and other modules to forget learned values and other key settings. This, in turn, may require using a scan tool to reset or recalibrate certain systems. Don’t make extra work for yourself by forgetting this key bit of information.When measuring a key-off current drain, keep in mind that opening a door, the trunk or turning anything on may wake up certain modules and increase the key-off current drain reading.If the key-off current drain is higher than normal, the problem may be a light or module that’s staying on, or a relay that is not switching off. Finding the fault usually means pulling fuses one by one until the current reading drops down to a normal reading.STARTER CIRCUIT
Now, let’s say the battery tests good, the charging system is working normally and there are no abnormal current drains on the battery. But the engine won’t crank when you try to start it. Nothing happens when you turn the key to the start position (or press the start button). A no crank with a good battery means there is some kind of problem in the starter circuit.
Voltage may not be reaching the starter relay, the starter solenoid or the starter motor. The cause may be a bad ignition switch, an open park/neutral safety switch (if the vehicle has an automatic transmission) or an open clutch pedal safety switch (if it has a manual transmission).Diagnosis should begin at the starter relay. If the relay is not receiving battery voltage when the key is turned to start (or the start button is pushed), the fault is upstream of the relay. You would use a voltmeter or test light to find out where the voltage is not getting through. Is there voltage to the ignition switch or start button? Does voltage flow from the switch or button when you try to start the engine? Is there voltage to the park/neutral or clutch pedal safety switch? Does the switch pass voltage when it should? If the switches are all OK, but there is no voltage to the relay, the fault would be in the wiring or a loose or corroded wiring connector.If power is reaching the relay but nothing is happening, you can test the relay with an ohmmeter (refer to the test values and terminal connections provided by the vehicle manufacturer), or you can simply swap or replace the relay to see if that solves the problem.If the fault is not the relay, the next check would be the circuit between the relay and starter solenoid or starter (depending on how the system is wired). Loose or corroded connections can strangle the flow of current to the starter. Using a voltmeter to do some voltage drop tests can help you find bad connections.VOLTAGE DROP TESTING
A voltage drop test is the only effective way to find excessive resistance in high-amperage circuits. As a rule, you should see no more than 0.5-volt drop across a high-current connection, and no more than 0.1 volts across a low-current connection. Ideally, you should see no voltage drop at all.
To perform a voltage drop test, the circuit needs to be on with current flowing through it. You then use a digital voltmeter (DVM) to measure the voltage drop across each connection in the live circuit. Voltage always follows the path of least resistance, so if the connection being tested has too much resistance, some of the voltage will flow through the voltmeter and create a voltage reading.If a connection is good (clean and tight with no resistance), you should see little or no voltage drop (zero to less than 0.1 volts). But if you find more than a few tenths of a volt drop, it indicates resistance and a need to clean and tighten the connection.It’s amazing how many times bad connections are overlooked because they “appear” to be OK. But appearances are often deceiving, and the only way to know for sure whether or not you have good connections in an electrical circuit is to measure the voltage drop across those connections. This applies to battery and ground cable connections, starter, solenoid and relay connections, and wiring harness connections.STARTER CHECKS
If voltage is reaching the starter but it isn’t cranking, or is cranking too slowly (most engines need to be cranked at least 250 rpm or faster to start), the problem is likely a bad starter.
Starter current draw can be tested on the vehicle or on a starter bench tester, and compared to specifications. A good starter will usually draw a current of 60 to 150 amps, depending on the size or power rating of the starter. Some “high-torque” starters may draw more amps, so always refer to the manufacturers’ test specifications. When a starter draws too much current, it may pull so much power from the battery that the ignition system won’t fire. The engine cranks but it won’t start because there is no spark (or too weak a spark).If the starter spins freely (up to several thousand rpm) and the amp draw is within specifications, it should be capable of starting the engine — unless there is a mechanical problem with the drive mechanism, drive gear or damaged teeth on the flywheel.If the starter does not spin freely, or draws an unusually high or low number of amps, the starter has reached the end of the road and needs to be replaced.An unusually high current draw and low free-turning speed typically indicate a shorted armature, grounded armature or field coils (possibly due to overheating from excessive cranking), or too much friction within the starter itself (dirty, worn or binding bearings or bushings, a bent armature shaft or contact between the armature and field coils). The magnets in permanent magnet starters can sometimes break or separate from the housing and drag against the armature.A starter that does not turn and draws a high current may have a ground in the terminal or field coils, or a frozen armature.Failure to spin and zero current draw indicates an open field circuit, open armature coils, defective brushes or a defective solenoid.Low free-turning speed combined with a low current draw indicates high internal resistance (bad connections, bad brushes, open field coils or armature windings).NO-CHARGE
If the charging system is not putting out enough current to keep the battery charged, the fault may be the alternator, the voltage regulator (or control circuit in the PCM depending on how voltage is regulated), or bad wiring connections.
If you don’t see at least 13.5 volts when you check charging voltage at the battery with the engine idling, check the wiring connections at the alternator — not just visually or by wiggling the wires or connectors, but check for excessive resistance by doing a voltage drop test. Many so-called alternator problems turn out to be nothing more than a bad connection at the alternator or a bad wiring harness. Alternator output can be tested on the vehicle or on a bench-tester. As a rule, an alternator should produce 90% or more of its rated output by 2,500 rpm. The charging curve will vary from one application to another, but if the output is less than specification, the alternator needs to be replaced.The fact that an alternator is producing voltage doesn’t mean it’s producing enough current to meet the vehicle’s electrical needs and keep the battery recharged. An alternator that is rated at 120 amps at 2,000 rpm, but is putting out only 40 or 50 amps, is a weak alternator that needs to be replaced.Common alternator problems include worn brushes and slip rings, shorts or opens in the stator or armature windings, broken or melted electrical connections, and bad diodes in the rectifier (diode trio). Diodes can fail from too much heat or current. The diodes in the back of the alternator convert alternating current (AC) to direct current (DC). If a diode shorts internally, some of the AC current can leak into the electrical system, causing a voltage pulsation. At the same time, a shorted diode may allow current to flow backward through the alternator causing the battery to run down when the engine is not running. When an alternator’s output is displayed on a digital storage oscilloscope, the waveform should look like a series of even humps. Missing humps would indicate bad diodes and a drop in current output.If an alternator tests bad, make sure the replacement alternator (new or reman) has the same or higher amp rating as the original. If the replacement comes with a pulley (some don’t), make sure it matches the original (same diameter, width and belt type). In some situations, you may want to recommend upgrading to a higher output alternator if the stock alternator can’t produce enough juice to power a high-wattage aftermarket sound system, off-road lights or other electrical accessories.


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