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What would adding a resistor and diode to position sensor switch circuit?
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DougSpindler:
I pulled my console apart and it's a microswitch.  Mechanically the switch in my car was working fine.  Could it be the contacts are getting burned?  Over voltage or current?  The resister is to reduce the current and the diode to dissipate a voltage spike?
 
Take a look in the this video.

bdunham7:

--- Quote from: DougSpindler on November 06, 2021, 08:00:45 pm ---I pulled my console apart and it's a microswitch.  Mechanically the switch in my car was working fine.  Could it be the contacts are getting burned?  Over voltage or current?  The resister is to reduce the current and the diode to dissipate a voltage spike?

--- End quote ---

OK, so reading more closely, I see that step 3 in the service procedure has a 'park switch contact cleaning procedure'.  So yes, there must be some issue that arcs the switch contacts and this is their patch.  Very sketchy, IMO.  There is also a release solenoid in the circuit that only allows you to shift out of park under the correct circumstances.  If you dig up a schematic it will probably all be much clearer.  There should also be  PRNDL sensor of some sort somewhere, but it appears that this isn't implicated in this problem.
floobydust:
What century is this where a microswitch causes so much hassle and mayhem going back 5 years, across multiple models: Chevy Volt, Malibu, Blazer, Traverse, Acadia. Corporate denial a problem? leading to a class action suit.  :palm:
"The cause of the condition may be the park switch in the transmission control (shifter) assembly not pulling BCM signal low to electronically show Park condition."
The switch requires soldering to replace, so it looks like the entire shifter gets replaced instead.

Nobody's ohmmeter readings of the "fix" GM stub harness 84733196 make sense. How do you get "basically a short" across a 100R resistor and diode? Need to see the Volt wiring diagram to fully understand what is going on.

Mechanic "operate the switch 50 times". Microswitches aren't usually that crappy, the contacts do wipe... unless this is super cheap i.e. copper leafs only. Would look like either not enough wetting current 1mA and contact cleaning/wiping action to overcome oxide buildup- for the case it's only switching a simple digital input to the BCM or ECU.

Or, some car models the Park Switch also feeds the Brake/Transmission Shift Interlock (BTSI) solenoid, so higher current could flow switching that. The switch is rated only 2A. In the case somebody at GM forgot the solenoid back-EMF diode, contact arcing would occur and likely damage the relevant BCM/TCM/ECU digital input as well. Inrush from any big capacitor filtering the DI seems not likely, EMC caps are 47nF or less.
The stub harness tries to cover all makes/models affected but it looks like the basics of having a TVS is not there?

Original microswitch is Omron D2HW-BL251H. The chinese are on this, selling replacement switch on Aliexpress for $3 lol.
NiHaoMike:
My guess is they had a bypass capacitor too high in value on the control module and the series resistor is a workaround so it doesn't pit the contacts.
floobydust:
But what's the diode doing? 100R is nothing for a DI that it warrants a shunt diode. The switch is carrying or breaking high/inductive current for some reason, which is killing it- if this oddball GM fix is correct and actually works verses replacing the switch/shifter.
My guess is it's the BTSI solenoid, usually controlled by the BCM for more safety and anti-theft etc. but the park switch can be in series for extra safety.
Then it looks like the "break after make" is the microswitch actually switching the solenoid (current), not the BCM because it is slow and later to act, in firmware, with its digital output.
Hard to tell because this is about 5 years of cars and at least than five different models.
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