Turn signal problem

[DaveO]

ok i have an 00 MGM LS and when i have my Hvac on my turn signals start blinking fast like I have a bulb out. I turn off Hvac and they work fine......any idea's?

[sly]

Check the dash grounds. I suspect there's a wiring problem (some wire from the HVAC and the LCM are getting crossed) but loose grounds can be a real PITA. They should be located behind the kick panels on both sides of the dash (several wires bolted to the body with ring terminals). Make sure those are not loose. I don't remember if the grounds are to the body for the tail lights or run all the way back up to the LCM. I'll see if I can remember to check my EVTM to see if there's anything else to check or it it may be a fault in the LCM when I get home.

[Kodachrome Wolf]

I know my alternator output can be a bit low at idle in drive and it’ll cause the LCM to go into fast flash mode. Once I start accelerating, it goes back to normal.

Some people have mitigated the issue by installing fresh bulbs, or slightly higher wattage ones compared to stock.

[sly]

That would make sense. Possibly the blower relay mod would help with this.

[DaveO]

Sly- I will look for lose grounds

Wolf- it will do it at any speed even going down the highway at 80 mph

What is the the blower mod?

Oh and 1 other tid-bit that not sure if it correlates or not, but when I put the Hvac (I have the auto Hvac) in "Floor mode" the air still comes out the vents.

[jaywish]

It would not hurt to check the grounds, battery and charging system before getting into anything else.

[DaveO]

Ok guys I have looked over and even installed a few grounds with no luck. Any other ideas???????

[IPreferDIY]

That would make sense. Possibly the blower relay mod would help with this.

... What is the the blower mod?

Oh and 1 other tid-bit that not sure if it correlates or not, but when I put the Hvac (I have the auto Hvac) in "Floor mode" the air still comes out the vents.

Yeah, what's the blower relay mod? Did you mean the headlight relay mod? I would recommend the latter for anyone regardless of whether they're having problems (it essentially reduces the current going through the original wiring and gives the headlights all the current they want through thicker wire connected to the battery through added relays), though I don't see it as a substitute for an unknown problem like this one. I've never heard of this particular problem before.

How many miles on the car? And what kind of climate has it been in? The issue with the vent is curious. It doesn't sound like the typical problem of bad o-rings in the control unit affecting things. I think the o-ring problem causes it to default to the defrost vents for everything.

[sly]

Blower sucks off a 30A fuse. If you set a relay to trigger on power to the blower and supply power from the relay hooked to the battery, you get much cleaner power to the blower and much less draw under the dash. This also allows the blower to keep at higher speeds when stopped at night with the AC on full blast as there's not the voltage drop from the ignition switch and all the wiring under the dash.

[IPreferDIY]

So basically the same idea as the headlight relay mod. I'd be more concerned about the effect of the blower on the other stuff, but whatever. Not sure I'll put it on my "to do" list just yet, since I generally keep the blower low. The one thing that comes to mind though is which wire is triggering the new relay? Isn't the one that feeds the motor using PWM? (at least on the EATC)

[jaywish]

Have you checked the charging system? Running voltage and static voltage? Battery condition? Do any of the auto part chains do this for you?
BTW are any of your bulbs swapped with LED?

[sly]

So basically the same idea as the headlight relay mod. I'd be more concerned about the effect of the blower on the other stuff, but whatever. Not sure I'll put it on my "to do" list just yet, since I generally keep the blower low. The one thing that comes to mind though is which wire is triggering the new relay? Isn't the one that feeds the motor using PWM? (at least on the EATC)

Nope. That's all down stream of the blower. The PWM is on the "blower motor resistor". The blower gets the power and then the "resistor" controls the speed and manual controls the fan switch directs which resistor the down stream power flows.

[GM_Guy]

I never looked, but does the blower motor still ground through the case on these cars? If it does, check or run a temporary ground to one of the mounting screws and see what happens. Had to run a dedicated ground to my blower motor in my truck, for me it was noise, but it also had the bonus of improving the blower output at low speeds.

Alex.

[IPreferDIY]

Something else to consider is cleaning the contacts on the blower motor that the brushes ride on. In my 2000 MGM, the motor started getting flakey and then stopped working altogether. I pulled the motor and cleaned the contacts and it worked again. The contacts were black, so I guess the buildup was blocking current flow. I never had a problem with the turn signals, but it's a simple thing to check/try. If your car has a lot of miles, a new motor might be in order.

A known problem that is probably unrelated is cracked solder joints on the EATC blower motor resistor. I had actually checked that on mine before checking the motor, and it was a PITA. Mine was okay, but I touched up the solder anyway and cleaned the contacts on the plug.

[sly]

I never looked, but does the blower motor still ground through the case on these cars? If it does, check or run a temporary ground to one of the mounting screws and see what happens. Had to run a dedicated ground to my blower motor in my truck, for me it was noise, but it also had the bonus of improving the blower output at low speeds.

Alex.

nope. Grounds back through the entire fan speed circuit. They're all 2-wire.