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justinsbg, Acura Mechanic
Category: Acura
Satisfied Customers: 913
Experience:  I have 10 years of automotive experience, an associates degree, and ASE certifications.
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I have a 2005 MDX with NAVI and RES. Last couple of days the

Customer Question

Good Morning Pearl,
JA: What is the model/year of your Acura?
Customer: i have a 2005 MDX with NAVI and RES. Last couple of days the VTM-4 light came on and stays lit. Lights are flickering on and off. NAVI screen sometimes not responding. A/C is cut out sometimes. I thought the alternator starts going but it reads 14.34V when idling and no charging sys light or check engine light is lit. I heard something like relay chattering by the trans shifter console. pls help.
JA: How many miles are on the car? Has the car been starting normally?
Customer: pearl, yes, starts no problem. Battery reads 12.72 V. vehicle has 94,872 miles
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I put my suspect on the alternator because my son said yesterday voltage did drop to 11 volts when idling but charging light. I do not want to change it out because of that. the VTM-4 light is what bothers me. do you suggest anything else to try I can do b/4 taking it to dealer?
JA: Anything else you think the mechanic should know?
Customer: no other symptoms so not sure whet else to add. air bag light also comes on and off. do you know what that chattering noise is under the trans shifter console?
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Acura Mechanic about your situation and then connect you two.
Submitted: 5 months ago.
Category: Acura
Expert:  justinsbg replied 5 months ago.


My name is ***** ***** I would be happy to help. To know what needs to be done regarding the VTM light you need to have the computer scanned. You can go by somewhere like Advance Auto and have them scan it for free. They will give you the code. You can then relay that code to me and I can help you with a fix.

Customer: replied 5 months ago.
Hi Justin, the owner's manual said not to drive far when the light is on. I will go to Advanced Auto to see what code has been set. Any suggestion what possibly has malfunctioned as there's no engine lights or charging system light lit? a/c compressor did cycles along w the a/c fan on and off? thanks. Wallace
Expert:  justinsbg replied 5 months ago.

There are so many things that can turn the VTM light on that it would be almost impossible to guess at the code. If you don't notice any driveability problems when driving then it's probably not anything too serious.

Customer: replied 5 months ago.
Ok. I'll drive to Advanced Auto and get a code read from scanning and report back.
Expert:  justinsbg replied 5 months ago.
Sounds good
Customer: replied 5 months ago.
Justin, just came back from Advanced Auto after the OBD scan. Result is "No Codes Found". Went to a repair shop and they also did an OBD scan and also found no codes. I duplicated the condition that turned on the VTM-4 light: started normal without ac on; 2. when AC switch is pressed, then the VTM-4 light came on instantly and the AC compressor, along with the 2 fans -cooling and condenser fans, started cycling on and off in 2-3 seconds interval. I put the gauge on the suction side and the refrigerant pressure reads normal at about 70 psi when the compressor is off (it did not stay on long enough to pump down). Lights again flicker and the trans shifter console area has clattering noise as mentioned before. This time aig bag light also faded in and out. 3. when AC is disengaged, lights stopped blinking. Alternator always read steady at 14.32V even with the AC on and interior and instrumental panel lights blinking. I checked the fuse box and did not find any blown fuse.
So what gives?
Customer: replied 5 months ago.
Any idea Justin?
Expert:  justinsbg replied 5 months ago.

This surely sounds like insufficient voltage. Try unplugging the alternator temporarily to see if the issue stops. Let me know what happens

Customer: replied 5 months ago.
Justin, note that the reading from alternator has also been at or above 14.32V.
I googled some more on "MDX VTM-4 and ABS along with other lights came on", a condition just like what I experienced and the culprit was a bad speed sensor and not what people always say it's the alternator or battery at issue. A bad sensor caused the integrated ABS, VSC, VTM-4 system to lose the reference voltage and set off the indicator lights.I like to get a refund because frankly I do not believe I received the expected service or guidance.
Expert:  justinsbg replied 4 months ago.

The alternator has inside of it several diodes. One or more of these diodes can fail and allow electrical feedback into the vehicles systems which will cause issues similar to the issues you are experiencing. When a diode fails the alternator will still typically charge so the charging voltage is not the problem. Unplugging the alternator would be a quick way to rule out electrical interference related to the alternator. I've been doing this a while so trust me.

Customer: replied 4 months ago.
How do you unplug the alternator? Do I unplug it before starting the car? How long should it be unplugged while the engine is running? What condition would be seen if it's diode problem on the regulator of the alternator?
Expert:  justinsbg replied 4 months ago.

Unplug the alternator before starting the car. It's best to do this while the engine is not hot because you'll be close to the exhaust manifold where it will be quite warm. After unplugging the connector start the car and see if the lights go out. I will include a picture of the alternator so you can see the connector. You'll have to pull back a rubber boot covering the connector.

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