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2007 Acura MDX with 215,000 miles. It’s my 20 year old son’s car. It’s been very well maintained over the last 14 years. While driving to work the vehicle’s battery light Illuminated on the dashboard and he got a “check charging system” notification in addition to several other system warnings. He drove home and parked it. The battery was reading 9-10 volts with the engine off; however it would start normally and the battery voltage at idle was 11.5 volts.

I replaced the 2 year old battery.The new battery’s voltage at idle was 12.6 volts but decreasing as the car ran.

I determined that the alternator had failed so I removed it and took it to a reputable remanufacturing shop where they replaced the voltage regulator, the rectifier and the brushes. I put the alternator back in the car, hooked up the battery and started the engine. I immediately got 6-7 system warnings and the nav system wouldn’t boot up. The Battery light and the check charging system was also illuminated. The battery voltage with the engine running was 17.8 volts! I turned the engine off and I’m the battery voltage was 13.1 volts but declining back to 12.6 volts.

Any idea what’s going on here? I’d appreciate some additional troubleshooting ideas. Thanks for your help.
Dan Cook
 

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Bad voltage regulator, why don't you buy rebuild alternator with new diodes too.. It is funny, when money is paid to do quality job and people who is doing this job every day, can not not get it right.
I hope your MDX did not suffer permanent damage. Buy reman from autozone. Good luck
 

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I would suggest spending a few extra dollars and buying a denso alternator. Look up Denso # 210-0580, that is the OEM unit. I went with an Advanced Auto “car quest” because I was able to get it locally. It looked brand new and perfect, came with a fancy quality check list, low rpm voltage test, high rpm voltage test. I installed it and it worked fine for about 2 months. Now at low RPM “check charging system” anything past 6000rpm “check charging system. The belt and tensioner are brand new and installed at Acura.

I’ll never buy an off the shelf alternator again, but Denso or take it to Acura.


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“I determined that the alternator had failed so I removed it and took it to a reputable remanufacturing shop where they replaced the voltage regulator, the rectifier and the brushes.”

dzionassi: So you think the voltage regulator has failed again? Or, perhaps, the guy who remanufactured it put in a bad voltage regulator?

techmechanic: It is a Denso alternator, original to the car. Honda CSD69, Denso USA. Repaired by a local guy who I trust.

Update: I left the battery connected overnight and it’s now reading 11.6 volts, engine off. Help.


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Ok, two things:

1) A remanufactured OEM Denso alternator only costs $190 from Rockauto. And you get half of that back with core. You can't beat that.
2) If you battery is draining with engine off, diagnose what's draining the battery and rectify it. Most likely culprits: 1) HFL unit; 2) A/C relay; 3) CD/DVD changer mechanism failing.

Good luck!
 

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AcuraAddicted: Thanks for responding. My HFL was previously disconnected and the A/C relay was recently replaced, 3/28/2020. The CD/DVD changer did make a lot of noise when I reconnected the battery. I’ll investigate that.

Interestingly, after I started the car this morning the alternator battery appeared normal; charging the battery at 13.2-14.4 volts (It varied based upon which electric accessories I was operating). The battery charged to 12.6 volts and is currently holding that voltage.

I then disconnected the battery to again check the voltage (still 12.6v). When I reconnected the battery the car alarm sounded and wouldn’t turn off even when I started the car. The only way I could get the alarm to stop was to put the key in the driver‘s door and turn the key to the unlock position. The alarm issue disappeared after several engine starts and everything appeared normal so I decided to go on a test drive. As I accelerated out of the driveway I got 4 warnings:

Check brake system
Check ABS system
Check airbag system
Check VSA system

I‘m currently troubleshooting these four warnings. All VSA, Brakes and Airbag fuses are good-to-go.

I read the following post and think it might be Important: “yup just replacing the battery or gettin it fully charged will fix the problem. all those lights appeared becuase the battery voltage drops below 5.0v which too low to operate the control units for each system so it triggers the lights on...happens all the time“
 

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AcuraAddicted: I definitely wish I’d gone with RockAuto. (HFL disconnected several years ago; A/C relay replaced two months ago; I’ll check CD player....it seems to search for discs a lot).

dzionassi: The “trusted“ repairman might have installed the wrong rectifier. The receipt lists an INR434 that‘s designed for a 140/160 amp Denso for Dodge/Chrysler/Jeep. I think the correct part for Acura’s 130amp Denso is the INR424. Any idea what the wrong rectifier will do to my car? Voltage is fluctuating between 13.6 and 15.8 and I’ve got five warning lights.

Thanks,
Dan
 

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AcuraAddicted: I definitely wish I’d gone with RockAuto. (HFL disconnected several years ago; A/C relay replaced two months ago; I’ll check CD player....it seems to search for discs a lot).

dzionassi: The “trusted“ repairman might have installed the wrong rectifier. The receipt lists an INR434 that‘s designed for a 140/160 amp Denso for Dodge/Chrysler/Jeep. I think the correct part for Acura’s 130amp Denso is the INR424. Any idea what the wrong rectifier will do to my car? Voltage is fluctuating between 13.6 and 15.8 and I’ve got five warning lights.

Thanks,
Dan
Just go back to "tursted" man and ask him to make it right. Or get reman from autozone, they are refurbished denso units. You will get like $70 core for old one. They have 15% of now with most items next day free shipping.
High voltage usually is voltage regulator fault, low voltage means bad diode...
 

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Those four systems are extremely sensitive to voltages. Anything wrong and they all shut down and light up the cluster.


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Discussion Starter #10
Update: I removed the alternator from the mdx and took it to Advance Auto for a second opinion. It checked “good” twice. I returned the alternator to the trusted repairman and he ran it on his test bench for four hours at variable speeds and variable power draws. It passed every test. I reinstalled the alternator into my 2007 MDX, started the engine and the vehicle is behaving exactly as before: After starting the engine the voltage across the battery terminals was initially 17.7 volts. The speakers were popping, the dashboard lit up with Brakes/Airbag/ABS/VSA/Charging system/SH-All Wheel Drive Warnings. I installed a known-good battery and started the mdx.....exact same results.

QUESTION #1: There‘s a four-pronged plastic connector that plugs into the back of the alternator, where do the four wires in the connector go and what information is the alternator receiving from other sensors? Is there an electrical schematic of this system?

QUESTION #2: Why would the known-good battery voltage be 12.5 volts when not connected to the mdx but drop to 12.1 volts immediately after connecting the battery cables?

Thanks.
Dan
 

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Twice you've shocked your MDX's "brains" with 17 volts. Stop that!
Don't do it a 3rd time.
Accept your monetary loss and buy a rebuilt alternator from "Car Quest" or "Napa".

Did you know that a car's computer can be damaged if you jump start it a certain way.
The wrong way:
You use jumper cables, you connect them to you car and another car that is running, you start you car.
Your alternator is part of this path and the 2nd car's alternator is also part of the same path. Having 2 alternators connected to the same path can damage the computer on both cars.

The correct way:
Connect the jumper cables, start only one car, let the dead battery absorb current for 20 - 40 minutes. Disconnect the cables, start the dead car.

Will you automatically damage the computers every time...no, but if a regulator or diode is shorted, it will happen.
Of course this does not apply to old cars that do not have computers.
 

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dan, looks like there is a problem with the alternator drawing down current with the car off and and as well not regulating the voltage to a MAX of 14.4V. Sounds like it's time to go back to the rebuild shop with the car and show them the issue in person.
 

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Discussion Starter #13
csmeance: I agree. Yesterday I put an ammeter on the negative side of the battery and I was losing 3.5 amps. I pulled all the fuses Individually and couldn’t identify the source of the draw. Good chance it’s the alternator.

Stupid Question of the Day (SQOTD): Is there a grounding wire that attaches directly to the alternator? If ”no” then is the alternator grounded via the strap on the drivers side of the engine?

As for the overvoltage, it’s either a bad ground, a bad signal from the PCM or, like many have said, a second failed voltage regulator. I’d love to drive the mdx up to the repairman but I’m afraid I’ll fry the electronics. I’m leaning toward ordering a refurbished RockAuto alternator like carpayment4life recommends. I’ll deal with the repairman afterwards.

Answer to yesterday‘s QUESTION#1
Terminals & Modes: The voltage regulator utilizes five terminals: Ignition (IG), Control (C), Field Reference (FR), Battery (B), and Lamp (L). The B terminal is the high current circuit that's responsible for charging the battery. The other circuits are located in a single connector and are responsible for controlling the voltage regulator located within the alternator.
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Discussion Starter #14
I’m closing this thread out. It was the alternator all along. I purchased a replacement alternator from RockAuto, installed it and it works perfectly. Thanks, everyone, for the assistance.
 
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