Reatta in Germany - Headlight problems

[kdirk]

I've not found any functional difference in the headlamp modules among any of the four years of production. I have substituted 91 modules in 88's and vice versa with no issue. I will note that in two cases after rebuilding headlight motors and reinstalling them on car I had issues where one or the other wouldn't cycle initially, as though something was out of sync. After hand operating them open with the knob and turning the headlamps on and off a couple of times it began to operate normally. Still not certain what the cause of that was.

[Ronnie]

That's good to know Kevin in case I ever have to find a new module. Thanks for posting.

[2seater]

I've not found any functional difference in the headlamp modules among any of the four years of production. I have substituted 91 modules in 88's and vice versa with no issue. I will note that in two cases after rebuilding headlight motors and reinstalling them on car I had issues where one or the other wouldn't cycle initially, as though something was out of sync. After hand operating them open with the knob and turning the headlamps on and off a couple of times it began to operate normally. Still not certain what the cause of that was.

 

Cool! Perhaps it is only the wiring that is different but you would know the electronic aspects far better than me.

[kdirk]

I'd add that the harness at the module (located in the driver's front fender) is the same all four years as well, meaning the the two plugs and wiring color code are the same. I've not looked closely enough at the entire harness on car to see if there are other differences upline and/or downline on the headlamp harness.

 

My scrub 88 had the headlamp motor wiring rigged when I first bought it to run both motors from one side of the module (wiring for passenger side motor was spliced to driver side motor circuit). This was clearly done as one half of the the module was scorched out internally. To my surprise this worked for several months until I had time to repair the harness and change the module. That was all done when I rebuilt both motors, so I could remove all the piss-poor wiring zip tied to the radiator and cooling fan shroud that had been rigged in previously. The system has worked flawlessly ever since.

[2seater]

Interesting. I have no way to confirm the harness but I was led to believe one of the yellow wires for pre-90 had a black trace vs two yellow for the later? Likely it matters not since they are connected somewhere? All good info.

[Aztec62]

Hi,

Had a look at my headlight door problem today. I have checked the voltages on both motors during the opening and closing sequence with the help of an oscilloscope. I have tapped the wires directly at the motors.

 

First the left (operational) motor:

Closing sequence:

One can easily see how the 12V DC voltage is pulsed. The whole sequence lasts about 700 ms.

 

Now the right (non operational) motor:

Only half as much voltage at the motor at best! Small wonder nothing happens.

Next I tried another door module. No changes.

Turning the knob by hand during door opening/close did not help either.

Since I already knew the right motor was good ( I had checked it with 12 VDC connected directly), the error could only be in the wiring. After a short search I have found where:

Nicely visible the badly corroded copper strands of the wire.

After repair both headlight doors opened and closed nicely with the H4 bulbs installed.

At last!

It was good I had a oscilloscope at hand. The different voltages were not visible with a digital voltmeter. Maybe with an analoge one (with a pointer gauge), but I do not have one anymore.

 

Thanks for all the valuable help!

Henning

[2seater]

Simply awesome. I never thought to use my small O-scope for that purpose. Amazing how the two have obvious differences. Thanks for sharing the result.

[kdirk]

Nicely played Henning. Having a full complement of diagnostic equipment is almost required to be truly self sufficient in troubleshooting these cars. Wiring issues are more common now given age, and that is one reason I have replaced almost all the split loom in the engine bays of all my cars. This reduces the chances of chafing and melt damage to wiring, resulting in the sort of problem you just encountered.

[Ronnie]

Good job troubleshooting the problem. I don't have an Oscope so I couldn't have found it that way. I would have started by wiring a headlight bulb in the circuit for a load and then checked the voltage. With the circuit under load the voltage, or brightness of the bulb, would have indicated a problem with the power going to the motor.

[Aztec62]

Ronnie,

I think your way would have worked, too.

But I wanted to see the pulsing voltage, hence the scope.

 

Henning

[Ronnie]

I wonder why it pulses? Could it be a way of controlling the speed of the motors?

[Aztec62]

Well Ronnie,

I have tried to explain why the voltage pulses in a previous post. Maybe my English language was not good enough.

Somebody else want to chime in?

 

Henning

[Ronnie]

Well Ronnie,

I have tried to explain why the voltage pulses in a previous post. Maybe my English language was not good enough.

Somebody else want to chime in?

 

Henning

 

Your English is fine. Sometimes I forget what all has been written up to this point.

 

I guess I should have phrased my question differently. What I was trying to ask is: why would GM engineers choose to design a system that uses pulses for your '91 as feedback to determine when the motor stops turning instead of just watching for a high current condition to indicate the motor had stopped. The latter is what I had always thought happened. My Field Service Manual seems to indicate that as well.

 

The down or up coasting movement of the door keeps them spinning until the voltage is pulsed high again and the door continues to open/ close.

I guess that is the reason why the headlight doors are made of alloy and not of pressed steel.

This makes them a little heavier (= more momentum) which helps the down/up coasting movement of the door.

No DC voltage from the motors means motor stopped turning because door is open, closed or jammed.

The module will then switch its voltage off.

 

It sounds to me like it is a smarter, more sensitive way to check the door position than sensing the current.

It might put less stress on the door linkage, gears and on the motor.

 

 

Sorry but I don't agree with your theory that a heavy headlight door's momentum when coasting will keep the motors spinning. There is just too much gear reduction between the large gear and the worm gear for the weight of the door to make a difference... in my opinion.

 

Perhaps your gearbox is made different from my '88's. I don't think you could stand on the headlight door on my '88 model and make it go down enough to spin the motor without electrical power helping it move. Worm gear drives just aren't intended to work that way. If the weight of the door was intended to keep the motor moving GM would have used straight cut gears on the motor and output shaft instead of helical cut gears. Worm gear drive boxes, in my experience as a machinist, are designed to hold the output shaft in position when the motor stops, which is what is needed in the actuation of the headlight doors.

[2seater]

I know little about this subject other than an empirical observation. If your spin the motor by hand, you can usually feel the windings passing the case magnets. I suspect this effect can be observed with the fast reacting O-scope, where a digital VOM will show an average?

[Aztec62]

I know little about this subject other than an empirical observation. If your spin the motor by hand, you can usually feel the windings passing the case magnets. I suspect this effect can be observed with the fast reacting O-scope, where a digital VOM will show an average?

 

The effect you have felt is called electrical induction and is what makes any electric motor turn.

When you spin a electric motor with permanent magnets in the case, the motor acts like a dynamo and provides a voltage at the plus and minus terminals of the motor. It is exactly like a dynamo you have on a bicycle for the light.

 

The headlight motors on a Reatta receive a high-low signal (12V DC present-not present) from the door module.

The intervals are very short, just a few milliseconds. When the voltage is high, the doors start to open/close. When the voltage is low, the motors continue to run for a very short time and send the voltage they produce in that time to the module which measures the voltage. When the motors arrive at the stop, the motors are unable to spin and provide no voltage and the module determines that the doors have arrivied at the mechancal stop. The door module will not send any high signal any longer.

 

Ronnie is right, the flow of power trough the gears can be one way only, from motor to the mechanical door linkage.

It is not possible to turn the motors when you try to move the doors by hand.

But during the opening/ close sequence, the motors still continue to run with a low voltage signal, but only for a very short time. Apparently, this time is enough for the door module to measure the voltage generated by the motors.

 

This is how GM describes the function in the 1990 manual, too.

Like I said, it is a little magic, but it works.

The reason to change from measuring the voltage instead of the current I do not know.

But I think, GM wanted something a little more sophisticated which might put a little less stress on the whole system.

 

Henning

[2seater]

I think something just flew over my head :) I think I get the basic concept you are talking about and actually have a starter/generator on my golf cart. By the way, your English is better than mine.

[Ronnie]

... The headlight motors on a Reatta receive a high-low signal (12V DC present-not present) from the door module.

The intervals are very short, just a few milliseconds. When the voltage is high, the doors start to open/close. When the voltage is low, the motors continue to run for a very short time and send the voltage they produce in that time to the module which measures the voltage. When the motors arrive at the stop, the motors are unable to spin and provide no voltage and the module determines that the doors have arrivied at the mechancal stop. The door module will not send any high signal any longer.

 

 

OK, I think I may be starting to grasp the concept of the pulses from the motors being used to stop the motor. I may be wrong but I think the pulses (sent BACK FROM the motor to the module) are allowing the motor to act as a crude encoder to keep track of the  movement, or lack thereof, of the motor in order to know if it is turning.

 

I have worked around a lot of computer controlled machines that use an optical encoder mounted on the end of a DC motor's shaft to keep track of the movement of the cutting head on the machine to position it in the proper position (within +- 0.001").  The encoders sent pulses that were counted by the computer to know the exact position of the motor(s) at all times.  Some of the machines were made in Germany by a company called Hegenscheidt that you might be familiar with.

 

Perhaps GM didn't want to spend the extra money on adding an encoder to the motor so they decided to use pulses from the headlight motor as feedback to determine if the motor has stopped turning.

 

All this is just speculation on my part of course. I'm just trying to understand how the system works and why current sensing was not good enough to stop the motors when the doors reach the end of their travel.

[Aztec62]

Ronnie,

I think you are correct.

By the way, the Hegenscheidt Company is still around.

You can find them in the USA, too:

http://www.hegenscheidtmfd.com/

 

Henning