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Discussion Starter · #1 · (Edited)
Since I've been having charging problems and I narrowed it down to the alternator I figured I'd organize everything I documented and written down and put together a guide on diagnosing the charging system. Charging issues seem to be a common problem around here and these cars are a little different being that they turn the alternator on and off through ELD (electrical load detection). I'll try to make this as easy but as complete as possible and continue to edit with any suggestions. I’ve gathered most of this information from all over the place and verified this on my 2003. I can't confirm all this on the newer Gen1 models though. I want this to be an easy to access/understandable way to diagnose these cars. Maybe we can sticky this as well.



Step 1: Check your battery posts and terminal clamps.
  • Clean any corrosion on the posts (this can affect charging)
  • Check that the clamps are snug and secure. Loose clamps will result in a poor connection
  • Check the cables for fraying and damage. If they're damaged, you need to replace them before anything else.
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Step 2: Charge and test your battery with a battery tester
  • There are some affordable testers out there as well as many auto part stores will charge and test it for you for free if you take it to them. This will tell you the state of charge as well as state of health
    • State of charge is the current charge of the battery
    • State of health takes into account the overall health of the battery by comparing the specified cold cranking amps with the actual measured cold cranking amps, reserve capacity, and charge acceptance
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Step 3: Check your main fuse in the fusebox under the hood
  • This is a 120amp fuse. If it's blown it cuts off the alternator positive to the battery and the car will not charge. If blown, check why it’s blown, don't just replace.
  • A simple continuity test across the left and right side of the fuse will verify it is still good.
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Step 4: Check your drive belt
  • Check for the following and replace if needed:
    • Intact
    • No apparent glazing
    • Slipping
    • Proper Tension: If poor tension; check/replace your tensioner
  • Blue circle in the image below is your alternator pulley and red circle is your tensioner
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Step 5: Check all engine compartment grounds (common issue)
  • There are three main grounds that are all known to oxidize/split and lose connection in these cars. Clean/replace as necessary.
    • Engine to Body (Green traced in image below)
    • Body to Negative Battery Terminal (Blue traced in image below)
    • Battery Negative Terminal to Transmission (Red traced in image below)
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Step 6: Check alternator power wire
  • On the back of the alternator there is a single threaded post (B) that has a wire that supplies the positive charging voltage. This goes from the alternator to the fuse box under the hood where we previously checked the 120 amp fuse. This cable is traced in yellow in the image below. From the fuse box it goes to the positive battery post. This cable is traced in purple. Check all these connections/wires for damage/fraying. Replace as necessary.
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Step 7: Check alternator bolts are secure
  • This is a simple check to verify the alternator is not loose on the bracket/engine.
    • The alternator has three bolts circled in red below. One long bolt on the bottom and two on top (one for engine, one for bracket). Give these a quick check to verify they are snug. The alternator grounds through the engine and requires a secure connection.
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Step 8: Voltage drop test (Multimeter required)
  • Using a mutlimeter perform a voltage drop test across the negative and power sides from the alternator to the battery.
  • I recommend following Chris Fix's guide starting at 4:30. Disregard his comments about charging voltage being 14.2-14.7V. Honda uses ELD (electrical load detection) to detect load and shuts off the alternator when not necessary to save fuel, so you will not always see 14+ V and this is normal. We will look into this at a later step.
 

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Discussion Starter · #2 · (Edited)
Step 9: Look at Live Data with a Scanner

  • This is where you can get an idea of what the PCM/battery/alternator/ELD is doing at a quick glance. With Honda specific scanners you can view live data of the following:
    • Battery Voltage
    • Alternator duty cycle (How hard the alternator is working as a %)
    • ELD sensor load (How much load the PCM is sensing is being pulled through the car's circuits from various accessories like AC/defroster/etc.)
    • What PCM is commanding the alternator to do (turn on to 14+V or turn off to ~12V)
  • You want to setup your specific scanner to read the above live data. Drive the vehicle and you will see how as the load at the ELD sensor changes, the PCM will switch the alternator control voltage to high/low (charge and turn off) as needed.
    • Things to look for:
      • While cruising at moderate speeds with no accessories on, the PCM will cycle off the alternator as needed, you should see the Alternator control switch to ~12ish range when it’s off and bump up to 14+ when charging is needed.
      • Check that the ELD load is changing as you turn on various accessories such as your headlights/defroster/air conditioner. As the ELD senses an increase in load, it will turn the alternator on if it is off and you should see the battery voltage and alternator load% jump as well.
      • If you don’t see any changes on the ELD load reported when you switch on accessories, there is an ELD issue you need to diagnose that I will not be covering here.
      • If the ELD load changes and the PCM is commanding the alternator to go high but battery is still low. You need to proceed below to rule out faulty circuits heading to/from the alternator and check the alternator.
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Step 10: Understanding the 4 pin circuits that control the alternator

  • This is where things get a little more complicated. There is a 4 pin connector on the back of the alternator that controls/sends information to the alternator between the PCM (Powertrain Control Module). These are the wire colors and their functions/how they work/communicate:
    • White/Blue (Lamp Indicator): This is the low voltage warning lamp circuit for the dash light. You should see 0V when engine is off in Position 0, 12V when engine is off and ignition in Position 2, and 0V when engine on and voltage is good (this will also show 12V if running and the voltage is low (i.e. battery bad/alternator not charging; when the dash indicator is illuminated).
    • Black/Yellow (Ignition switch): This is what supplies the alternator voltage regulator power. It comes from the ignition switch. When the ignition is in Position 0 no power is sent to the alternator. When the ignition is in Position 2, it sends 12V to the alternator.
    • White/Green (Control): This circuit is how the PCM turns on and off the alternator to save fuel. The alternator supplies 8V's to the PCM at all times when ignition is in Position 2 and 0V when in Position 0. When the PCM decides to turn off the alternator it pulls this 8V circuit low to 0V. When the PCM wants the alternator on, this circuit is pulled high to 8V.
    • White/Red (Field Regulator): This is how the alternator tells the PCM what it's duty cycle/load is. The PCM supplies a constant 5V to the alternator when the ignition is in Position 2. The alternator then pulses this high/low, represented as a rectangular wave. The duty cycle/load is the time 5Vs is on divided by the time it it is off(0V). The duty cycle is a ratio and is how the PCM reads how hard the alternator is working. Below is an image of the general idea behind duty cycle.
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Step 11: Check Alternator Control Plug Circuits and Alternator (Multimeter and Oscilloscope Required)
  • Start by disconnecting the 4 pin connector on the back of the alternator with ignition in Position 0
    • Front probe the White/Blue lamp wire with multimeter set to DC Volts. Ground the other probe to the battery negative terminal. This should show 0V.
      • If this shows voltage you have a short somewhere and need to diagnose the lamp circuit.
    • Front probe the Black/Yellow ignition wire with multimeter set to DC Volts. Ground the other probe to the battery negative terminal. This should show 0V.
      • If this shows voltage you have a short somewhere and need to diagnose the ignition circuit.
    • Front probe all 4 wires with multimeter set to resistance. They all should show an open circuit.
      • If this shows a closed circuit/grounded, you have a short somewhere and need to diagnose that specific circuit.

  • Now with the 4 pin connector still disconnected, turn the ignition to Position 2 but do not start the engine
    • Front probe the White/Blue lamp wire with the multimeter set to DC Volts. Ground the other probe to the battery negative terminal. This should show 12V.
      • If this shows 0V there is an issue on this circuit. Check fuse #6 on fuse box. Check this circuit.
    • Front probe the Black/Yellow ignition wire with multimeter set to DC Volts. Ground the other probe to the battery negative terminal. This should show 12V.
      • If this shows 0V there is an issue on this circuit. Check fuse #6 on on fuse box. Check this circuit.
    • Front probe the White/Red field regulator wire with a multimeter set to DC Volts. Ground the other probe to the battery negative terminal. This should show 5V.
      • If this shows 0V there is an issue at the PCM/or the circuit going to the PCM. Check this circuit.


  • Turn the ignition switch back to Position 0 then plug the 4 pin connector back into the alternator.
    • Back probe the White/Green control wire with the multimeter set to DC Volts. Ground the other probe to the battery negative terminal.
    • Back probe the White/Red field regulator wire with the oscilloscope. Ground the other probe to the battery negative terminal. I won’t go into too much detail on how to use a scope. There are plenty of videos online on adjusting them.
    • Start the engine. You should see the following:
      • On the DMM you should see a constant 8V.
        • If you do not see 8V’s stop the engine, remove the connector and attempt to clean the contacts. Reinstall the plug and start again. Try cycling on the AC and check the OBD2 scanner to see that the PCM is indeed telling the alternator to go to 14+V. If 8V is still not present there is an alternator/regulator issue.
      • On the oscilloscope you should see a rectangular wave between 0-5V. The duty cycle should change with increasing/decreasing loads. (i.e. turning on lights/heater/ac/etc.)
        • If you do not see any waveform, stop the engine, remove the connector and attempt to clean the contacts. Reinstall the plug and start again. If the waveform is still not present/flatline, there is an alternator/regulator issue.
        • If the waveform does not change with loads there is an issue with the alternator/regulator.
    • Using a clamping DC amp multimeter, clamp onto the alternator B+ wire going to the fuse box.
      • With the engine still running you should see increasing/decreasing current from the alternator with changes in loads. This should occur with the change of the waveform/duty cycle on the oscilloscope.
        • This tests to verify the alternator is actually charging in response to the load it’s reporting. If no current is present when the alternator is told to turn on, you have an alternator problem.
      • Plug in your OBD2 scan tool, setup like previously mentioned, and look at what the PCM is commanding the alternator to do. If it is commanding 12.5, it is shutoff and your oscilloscope should show this on your duty cycle and alternator load on the OBD2 tool. Your amps on your clamp meter should also reflect this. Cycle on the AC if the alt is being commanded low, this load from the AC will have the PCM telling the alternator to go high 14+V. You should see a jump in your load on the alternator both at the OBD2 scanner and the oscilloscope. Also you should see a jump in current on the clamp meter.
        • If one of these things does not respond correctly, you have an alternator/voltage regulator issue.
 

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Discussion Starter · #3 · (Edited)
My personal charging issues/diagnosis.

I went through and verified circuits like above.

My alternator was showing 85+% load at all times even when the computer had told the alternator to turn off through the OBD scanner. When the computer told the alternator to turn on such as when I turned on AC/defroster/headlights, reported load still stayed high on the alternator and the battery voltage dropped into the low 12V's (Should be 14+V).
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What happened in my case is that the alternator voltage regulator waveform frequency is all over the place and primarily pulling high when on at random. The PCM interprets these random blips as the alternator working hard (aka 85+% load) This occurred even when the alternator was told to turn off.
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Lastly, my clamping meter also showed very little shift in current from ~20amps at any time no matter changes in draw (turning on AC, defroster, headlights) regardless if the computer told it to turn on or off.
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The probed control pin showed voltage changing (8V) when the computer told it to turn on and off so the circuit for control was working.
Ignition was supplying 12v to the voltage regulator when the key was turned to position 2 as it should
The lamp pin was showing 0V as the battery/charging voltage was still high enough to not trigger the battery light on the dash.

The main tell that it's the alternator/regulator is the issue is that the field regulator circuit waveform is all over the place regardless of being told what to do and changes in load on the alternator by turning on ac/defroster/lights along with a virtually constant 20 amp output that never shifts.

I have a Highoutput 240Amp alternator on order from Mechman and will report back when it's installed. (Note this is requires upgrading wiring and an ELD bypass to fully utilize safely).

I hope this helps others with their charging woes.
 

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Discussion Starter · #8 ·
For those interested in the ELD bypass this is the same fuse box we have and ELD unit.

Only change I plan to this circuit is to have my Auxbeam relay box trigger the external relay instead of having the headunit power on wire with an external switch. This way it’s 100% my control regardless if the radio is on or not.

 
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