vtm-4 light on steady (2003 Pilot)

[darrenJ]

My vtm-4 light in the dash (not the button to turn it on) is on all the time if the Pilot is running. I checked the codes and am getting 44 and 78 which are vtm-4 relay defective or wiring harness short or control unit defective.

When I checked the 4WD 20 amp fuse it was blown.
I put in a new fuse and it blew as soon as I put it in (note the ignition was off).

Now I am trying to isolate where the problem is.
I am thinking I will have to disconnect things one at a time working back to the axle to figure out where the problem is but the fuse costs 7.50 so it will get expensive.

Could a defective relay or control unit cause the instant fuse blowing?

Does anyone know where the VTM-4 relay is?
Does anyone know where the VTM-4 control unit is?

Any ideas on spots that might be shorted?

Other ideas?

Thanks.

[N_Jay]

20 amps is a lot of current, I would not use fuses or a circuit breaker as a diagnostic tool.

I would disconnect all the connectors you can get to and then put a light-bulb in the circuit where the fuse goes.

You can then reconnect parts one at a time and get a good indication which is causing the short while limiting the current.

Since it is an 20 amp circuit, I would use a headlight or fog light (50 to 60 watt 12V bulb)

[darrenJ]

Thanks, I will give that a try.

[darrenJ]

I could not find the source of the current draw so I took my pilot into the Honda dealer. They did some testing and could find nothing wrong. They tested the relay and found it to be good. They then replaced the blown fuse (the one I had already replaced and had blow immediately) and everything was fine.

Total cost at the Honda shop was $250 to diagnose and replace the fuse and reset the codes.

I still don't understand how the fuse could have blown with the ignition turned off. If the VTM-4 is drawing power while the ignition is turned off wouldn't that lead to a dead battery all the time?

My only thought is that when the fuse blew the first time it left something in a strange state. When I went to insert the new fuse something immediately drew current to try to go back to its normal state but blew the fuse in the process.

Possibly if I had disconnected the battery before inserting the fuse it would not have blown and I would have saved a trip to the Honda shop and $250.

Anyway I feel a bit silly having taken the Pilot in and having a fuse replaced for $250.

[N_Jay]

I'm betting an intermittent short.
Probably a wire where the insulation has worn off.

[darrenJ]

If it happens again I will update the thread.

Thanks

[darrenJ]

Looks like you were right. The VTM-4 light just came on again. Must be a short somewhere.

[darrenJ]

So I got the Pilot back from the shop today.

They recommended replacing the VTM-4 control module which all the codes so far have said could be the problem.
Cost for a used unit was $395.

Another $370 to diagnose the problem (already paid $250 so a total of $620 for diagnostics and replacing the fuse and the control unit so far)

Hopefully this does it or else my pilot might just spend the rest of its life as front wheel drive instead of all wheel drive.

Here is some info I found for getting diagnostic codes.

This link explains how to read the diagnostic codes without a reader and also how to reset them.
Honda/Acura VTM-4

This link has all the diagnostic code meanings.
http://www.rsgear.com/technical/articles/2006_12.pdf

[N_Jay]

Since the first "diagnostic" charge did not find a problem that showed up again, I would insist on it back.

[harley909]

Mine did the same thing.
Turned out the sender in the rear end was bad. When I changed it one of the 2 connectors (prongs) was broken off. It was stuck in the wiring harness when I unhooked it.
About a $40 item if I recall.

[darrenJ]

So far so good, the light has not come back on.

[darrenJ]

Argh, the light just came back on today. I really don't want to take it back to the Honda dealer as they seem to be pretty much just guessing and then replacing stuff. I can do that myself, thank you very much.

[dustino8]

Originally Posted by darrenJ

Argh, the light just came back on today. I really don't want to take it back to the Honda dealer as they seem to be pretty much just guessing and then replacing stuff. I can do that myself, thank you very much.

If my math is correct, you've given $1015 to the dealership and still have the same problem. I would definitely go back to the same dealership, and politely insist they correct the problem for no additional cost.

[N_Jay]

Originally Posted by darrenJ

Argh, the light just came back on today. I really don't want to take it back to the Honda dealer as they seem to be pretty much just guessing and then replacing stuff. I can do that myself, thank you very much.

Did it blow the fuse again?

[rocky]

I'm sorry you are having all this trouble. Going back to the original fuse blowing.....
Seems nobody really got to the bottom of that. Seems to me you need an intelligent mechanic rather than someone who reads codes and thinks the solution is replacing expensive ECUs.

Darren; Did you find out where that relay is located during the first visit to the dealer?

Does wet weather trigger the light to come on? Thinking rain, or melting snow. Snow especially with salt is an excellent conductor.

The most likely source of a short comes where wires to the ABS sensors due to the flexing they sustain in normal usage. Also any evidence of water leakage into the area where the ECU and other electronics are located?