Honda Odyssey Front Blower Motor with a twist

Front Blower Motor does not work.

2005 Honda Odyssey, EX-L
130,000 miles and I expect at least 170,000 miles more.

History – Over the past four years, the front blower motor has operated intermittently. I noticed that when the weather went through large changes (warm/humid to cold/dry or vice versa), the fbm would not run. The system behaved in the manner described by Honda owners in many of the forums online. After a period of time passed, the blower would function properly again until the next weather change.

About two months ago, the blower stopped working again and it has not returned to form since. The system again displays all the usual symptoms reported on-line. The rear blower works fine.

The controls on the dash seem to be fine (display changes appropriately as I select settings, vents open and close for heat or A/C or which vents I want open). Air flows through the vents selected when I am driving – I have a passive windshield defroster!

Here are the steps that I have taken during the past week:

  1. Bought a new transistor/resistor module, OEM Honda Part #79330-SDG-W41 (I checked with a local dealer for the correct part number). I installed it but there is no change in the system.
  2. I found information on-line to test the T/R. I checked the old one – Thermal Cut Out is intact and the resistance between posts 3 & 4 (lower pair when installed) is 1,500 ohms. I checked the new transistor and it read out the same.
  3. Fuses, relays, power to the blower, blower, ground beyond the transistor are all fine.
  4. I reconnected the T/R and fbm and let the fbm lay on the car floor. I started the car with the fan on. Each time I start the car (or turned the ignition ‘On’) the fbm tries to run, but stops in an instant.

The Rat is cornered – it’s in the the T/R and the control signal from the control panel to the T/R corner. If I bypass these elements, the fbm goes on and off as I select the fan On/Off from the control panel.

I have avoided going to the dealership to this point and refuse to give in until I have exhausted all possibilities under my control (along with my trusty $8 DVM). I am only out $120 for the transistor (wish I had known how to test it before buying it) and not an additional $85 for a fbm! I will continue to research the problem until a mechanic I trust tells me to give up the ghost and take it to the dealership.

I have listened to youse guys for years and trust your good intentions. I know you try to help solve the problems that folks share with you. That’s what I’m counting on now – your good will. I am looking for ideas to test that will either A. provide clues to what the problem is or B. solve the problem.


Respectfully yours and digging like a rat terrier,

Wilmington, DE

Sorry to appear ignorant, but what do you mean by blower motor? Heater, radiator fan, supercharger, turbo? from what ithink i read, it is the switch, motor, or variable resistor.

I’m a little confused with exactly what you’ve done. You bought a T/R module, but then you talk about how you “reconnected the T/R.” Does that mean you still have the old one in there, or did you replace it with the new one? This problem doesn’t seem all that uncommon and most of the solutions have been to replace the T/R. Sometimes electrical parts can be funny - they can test out OK when you’re looking at resistances with a multimeter, but then when a load is applied to them, they fail.

Barkydog and shadowfax,

Thanks for responding. I apologize for the confusion, but I have performed innumerable checks to try to isolate the location of the problem. Trying to boil it down to a few simple clear statements is challenging. I appreciate your attention to this problem.

The fbm is the Front Blower Motor in the interior of the cabin. It blows the air through the vents in the dash to heat or cool the cabin. It supplies air for the windshield defroster. The blower is located behind the glove compartment box.

The new T/R is still installed. I can relate to the tricky business with electronics. ( I have a Masters in Electrical Engineering and I am a dirty finger nail type - that could be part of the problem, too.) It is possible that the new T/R is bad.

My latest test was to unplug the connector from the T/R. I jumped from hot-to-ground across the connector. I started the car. The fan comes on ‘High Setting’. I selected A/C temps and cold air came through the vents. I selected Heat temps and hot air came through the vents. Of course, I had no control on the blower speed (I bypassed the T/R!).

This data points at the T/R (the usual and customary problem) OR the signal it gets from the dash control panel.

I have already dropped $120 on a new Honda Genuine Parts transistor/resistor component. I am not afraid to do it one more time. I just wanted to check other possibilities before I splayed my wallet open to the car repair gods.

It just seems odd that the blower would fail after big weather changes and after awhile it would begin to behave normally. This happened many, many times during the past 3-4 years. Something didn’t ‘just go bad’.

I appreciate your interest and attention to my woe-of-tale.

PS - I am a problem solver, more mathematician than engineer (more philosopher). I am not just a technician - I like novel problems in which to embed my attention to details.

I appreciate your interest and input. If I can fix it myself, it will make me happy.

I wonder if the problem with that transistor/resistor module isn’t inherent, especially since you mention that a bunch of people are having similar issues.
Maybe they are using the transistor to pinch of the current to the motor off in various steps and maybe that transistor isn’t cooled properly so it can’t handle it. Those junctions could get pretty hot when you have the fan on. Could it be that the designers designed it such that the car’s fan cools the device? The thing is under the dash and that area varies in temperature. Maybe there’s a systemic problem with that:
As the car is being cooled in summer with the AC on, that module is cooled as well. As winter sets in and the heat gets turned on, the junctions may get warmed by the higher ambient temperature.

Since you’re an EE, maybe just redesign that thing, put it on a simple board, pot the circuit and sell it as a replacement. If I had to replace a module more than once, that’s what I’d do.

I have considered bypassing the T/R with my own rheostat.

Everything works fine if I bypass the T/R except the blower RPMs.

Or I could drop another $120 - $180 on a new T/R.

I am open to diagnostics.

I am in total agreement that this is a design issue. Heat transfer has been a problem over the years for the T/R in Hondas - look at how the number of fins have grown on the heat sink over the years, I suppose there has been no ‘Recall’ on this problem because it does not present an immediate Safety Hazard. I think it does present a hazard because if the front fan doesn’t blow, then there is no windshield defroster/defogger.

Thanks for you thoughts.


Thanks for your input, RemcoW.


My next step would be to take your old TRI and stick it in another Odyssey with a known-working climate control. If it works, then your Odyssey’s TRI connections are screwed up somehow (dirt/carbon scoring/rodent damage). If it doesn’t, then take the new TRI out of your Odyssey and put it in the test Odyssey. If it doesn’t work, then something in your Odyssey is probably killing the TRI, (the test for this would be to take the original TRI from the test Odyssey that you know is working, stick it in yours, see if it works, and if it doesn’t, stick it back in the test Odyssey to see if it works and if it doesn’t you know it died in your Odyssey - but that might make the owner of the test Odyssey mad if your test busts his climate control) at which point you’ll be much more in your element for testing what would be killing it electrically than I am, so I’ll leave it there :slight_smile:

I like your thinking - controlled testing. Two factors and two levels.

I think the worst that could happen is that I buy another T/R for my friend who was willing to sacrifice their T/R. Cheaper than a dealer diagnosis. (Don’t get me wrong, I like my dealer. But it is expensive. )

I have considered going to a junk yard and stripping 4 or 5 T/Rs to see if I can get lucky. It is a pot shot at best. It doesn’t nail down the problem.

Besides temperature, the cause could be something like back-EMF, something you (armstrml) are no doubt aware of but for non EEs here, here’s the explanation:

As you are running a DC motor with a coil it in, it does not like to be turned off. It is inherent of the beast, described by a natural effect called self inductance. When the current through the coil disappears, the coil itself generates a fairly large spike in opposite polarity of what was applied originally.
You protect solid state electronics by putting a diode across the coil so that this voltage gets shorted through it.

It could very well be that they forgot to put a diode across the motor or have a diode across the module but the module physically too far removed for the spike to be subdued. It in effect takes that T/R module out periodically. Spikes like that do not always cause immediate failure but break the components down over time.

Should you replace that module, I’d put a diode across the fan motor. It certainly can’t hurt.

Does that thing have auto climate control? See if you can pull diagnostic codes. Hold the AUTO and OFF buttons down at the same time for at least 1 minute. If there’s a code, it should flash in the temperature display. It’ll be A-N alternating with numbers. The letters will correspond to the fault. The numbers are just separators.

With intermittent blower motor problems, it is often the motor itself. There is a bad spot on the armature and when the brushes are on that spot, the motor wont operate. It will eventually vibrate into another position and then the blower will work for awhile. Unfortunately, the motors are not meant to be taken apart anymore.

That’s a very good point, Keith. If you had access to the motor, he should be able to bump it a couple of degrees to see if it wants to turn.