Kickdown relay testing
Thread Starter
Race Car
Joined: Jan 2009
Posts: 4,665
Likes: 196
Kickdown relay testing
I have removed my kickdown relay so I can check to make sure it is working properly. The part number is 928.618.109.01 and it has a little wiring diagram on it.
The power flows though 30 - 87a, normally closed and the relay opens with a signal from the LH. On the diagram, terminals 31b, 15 and 31 all connect to the electromagnet that activates the relay. Terminal 31 connects to 30 with a diode, which tells me that this feeds the electromagnet on the relay 12v when the kickdown switch on the pedal is pushed down. Would that make terminals 15 and 31b ground terminals that get grounded by the LH to complete the circuit?
The power flows though 30 - 87a, normally closed and the relay opens with a signal from the LH. On the diagram, terminals 31b, 15 and 31 all connect to the electromagnet that activates the relay. Terminal 31 connects to 30 with a diode, which tells me that this feeds the electromagnet on the relay 12v when the kickdown switch on the pedal is pushed down. Would that make terminals 15 and 31b ground terminals that get grounded by the LH to complete the circuit?
Last edited by Cosmo Kramer; Sep 9, 2010 at 01:42 PM.
Rennlist Member
Joined: Feb 2002
Posts: 7,060
Likes: 42
From: Cambridge England
31b receives 12v square wave rpm signals from the LH, so to test you will need to feed an rpm signal in.
The contacts are fed igntion switched 12v via the kick dowon switch and when the relay solenoid is energised these volts are fed via 87 to the kick down solenoid on the auto 'box.
The relay coil is energised by a combination of the rpm circuit above, plus igntion switched 12v on 15 and the permanenty ground on 31 on the other end of the coil.
The contacts are fed igntion switched 12v via the kick dowon switch and when the relay solenoid is energised these volts are fed via 87 to the kick down solenoid on the auto 'box.
The relay coil is energised by a combination of the rpm circuit above, plus igntion switched 12v on 15 and the permanenty ground on 31 on the other end of the coil.
Thread Starter
Race Car
Joined: Jan 2009
Posts: 4,665
Likes: 196
OK I see now I wasn't looking at it right. 31 connects to 87A with the diode so it must ground through the kickdown solenoid. I wish there was a way to bench test this solenoid so I could know if it was working properly. If the magnet doesn't open the relay contacts it could be what is causing my issue with hitting the limiter on the 2-3 shift. If I lift on the gas pedal just a little bit slightly just before redline it will shift because I am releasing the kickdown switch.
Rennlist Member
Joined: Feb 2002
Posts: 7,060
Likes: 42
From: Cambridge England
I've never bench tested a kick down relay. I just found this explaination opf the relay operation on Theo's site..... from Wally Plumley
The only function of the kickdown relay is to ensure that the transmission shifts instantly and reliably at redline. The relay receives an RPM signal from the ECU at redline. The relay activates, opening the normally-closed contacts. This breaks the signal from the kickdown switch under the throttle pedal, causing the transmission to upshift instantly. As soon as the transmission shifts, the RPM signal disappears, the relay deactivates, the N-C contacts close, and you are back in kickdown mode (eager to downshift, reluctant to upshift).
Wally Plumley
So it appears that if the RPM detect circuit is not working (or rpm signal not appearing at relay) then this could cause the issue you describe.
The only function of the kickdown relay is to ensure that the transmission shifts instantly and reliably at redline. The relay receives an RPM signal from the ECU at redline. The relay activates, opening the normally-closed contacts. This breaks the signal from the kickdown switch under the throttle pedal, causing the transmission to upshift instantly. As soon as the transmission shifts, the RPM signal disappears, the relay deactivates, the N-C contacts close, and you are back in kickdown mode (eager to downshift, reluctant to upshift).
Wally Plumley
So it appears that if the RPM detect circuit is not working (or rpm signal not appearing at relay) then this could cause the issue you describe.
Thread Starter
Race Car
Joined: Jan 2009
Posts: 4,665
Likes: 196
Yes that is what I was thinking as well. If the relay is not energizing it is basically the same as having 30 and 87 jumpered. It could just be that I need a higher rev limit with the supercharger (currently at 6500, i have a new LH chip from Ken on the way bumping it to 6700). I would just leave the relay out and shift manually but when I do that my 1-2 shift drops to 4500 rpm. 
I've never bench tested a kick down relay. I just found this explaination opf the relay operation on Theo's site..... from Wally Plumley
The only function of the kickdown relay is to ensure that the transmission shifts instantly and reliably at redline. The relay receives an RPM signal from the ECU at redline. The relay activates, opening the normally-closed contacts. This breaks the signal from the kickdown switch under the throttle pedal, causing the transmission to upshift instantly. As soon as the transmission shifts, the RPM signal disappears, the relay deactivates, the N-C contacts close, and you are back in kickdown mode (eager to downshift, reluctant to upshift).
Wally Plumley
So it appears that if the RPM detect circuit is not working (or rpm signal not appearing at relay) then this could cause the issue you describe.
The only function of the kickdown relay is to ensure that the transmission shifts instantly and reliably at redline. The relay receives an RPM signal from the ECU at redline. The relay activates, opening the normally-closed contacts. This breaks the signal from the kickdown switch under the throttle pedal, causing the transmission to upshift instantly. As soon as the transmission shifts, the RPM signal disappears, the relay deactivates, the N-C contacts close, and you are back in kickdown mode (eager to downshift, reluctant to upshift).
Wally Plumley
So it appears that if the RPM detect circuit is not working (or rpm signal not appearing at relay) then this could cause the issue you describe.
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Mar 2002
Posts: 13,657
Likes: 616
From: Phoenix AZ
OK I see now I wasn't looking at it right. 31 connects to 87A with the diode so it must ground through the kickdown solenoid. I wish there was a way to bench test this solenoid so I could know if it was working properly. If the magnet doesn't open the relay contacts it could be what is causing my issue with hitting the limiter on the 2-3 shift. If I lift on the gas pedal just a little bit slightly just before redline it will shift because I am releasing the kickdown switch.
The active state of the kick down relay is when it opens the circuit.
Alan.
Trending Topics
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Mar 2002
Posts: 13,657
Likes: 616
From: Phoenix AZ
Well ...This thread got referenced elsewhere today. Whenever I see confusing data back in current use (even if from an ancient source) - I like to clear up the confusion.
Yes quite weird I know..
Alan
Yes quite weird I know..
Alan
Rennlist Stories
The Best Porsche Posts for Porsche Enthusiasts
Porsche Reveals Coupe Variant of the Electric Cayenne With a Fresh Look
Verdad Gallardo
10 Porsche Colors That Have More Personality Than Most People
Verdad Gallardo
Guntherwerks' Final Speedster Creation Is the Ultimate Porsche Restomod
Verdad Gallardo
10 Reasons I Hate Going to the Porsche Dealership (& the 1 Reason I Stay)
Joe Kucinski
Porsche Shakes Up The Nürburgring Lap Record Table Once Again
Verdad Gallardo
6 Ways the Porsche 911 GT3 S/C Redefines Performance
Joe Kucinski
10 Wildest Homologation Specials Porsche Ever Sold
Verdad Gallardo
Super Rare RUF BTR III Comes Out of Hibernation, Looking For a New Home
Verdad Gallardo
10 Porsche Opinions That Can Start a Fight
Joe Kucinski
Rennlist Member
Joined: Oct 2005
Posts: 5,244
Likes: 1,466
From: Gatineau, Québec, Canada
Not weird at all!
It's because of your great quality posts with very good advices that we can have better 928s.
Thanks and Happy New Year to you and to all great valuable members here.
It's because of your great quality posts with very good advices that we can have better 928s.
Thanks and Happy New Year to you and to all great valuable members here.
Burning Brakes
Joined: Mar 2013
Posts: 1,018
Likes: 219
From: Sunshine Coast, QLD,Australia
The diode here is a protection diode. 31 is always ground - in all normal operation the diode is reverse biased (not-conducting). Since the solenoid that is being driven is highly inductive - the diode protects against big negative spikes created from this coil inductance when the relay switch terminals open. Don't try to read any other functional significance into the diode... there isn't any.
The active state of the kick down relay is when it opens the circuit.
Alan.
The active state of the kick down relay is when it opens the circuit.
Alan.
If this is correct, does this mean that I should be able to measure a current at the kick down solenoid if I have current at the switch, and the switch is working ( which I have)?
Also, my kick down relay looks very "home made" compared to the images online. Does anyone know anything about these?
Thanks
Dawid
'87 s4 auto
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Mar 2002
Posts: 13,657
Likes: 616
From: Phoenix AZ
It doesn't work the way you think.
The kickdown is enabled by the WOT (kick-down) switch under the pedal driving the kick down solenoid through the normally closed relay - the relay operating (opening) causes the up-shift at the RPM limit by disabling the kickdown solenoid briefly - just as if you took your foot off the throttle (just off WOT) briefly.
Alan
The kickdown is enabled by the WOT (kick-down) switch under the pedal driving the kick down solenoid through the normally closed relay - the relay operating (opening) causes the up-shift at the RPM limit by disabling the kickdown solenoid briefly - just as if you took your foot off the throttle (just off WOT) briefly.
Alan
Burning Brakes
Joined: Mar 2013
Posts: 1,018
Likes: 219
From: Sunshine Coast, QLD,Australia
It doesn't work the way you think.
The kickdown is enabled by the WOT (kick-down) switch under the pedal driving the kick down solenoid through the normally closed relay - the relay operating (opening) causes the up-shift at the RPM limit by disabling the kickdown solenoid briefly - just as if you took your foot off the throttle (just off WOT) briefly.
Alan
The kickdown is enabled by the WOT (kick-down) switch under the pedal driving the kick down solenoid through the normally closed relay - the relay operating (opening) causes the up-shift at the RPM limit by disabling the kickdown solenoid briefly - just as if you took your foot off the throttle (just off WOT) briefly.
Alan
At the moment, I don't think my kickdown works, as I cannot get the double downshift when flooring the pedal at low revs in 4th. I am working my way back from the pedal to check and adjust everything.
What I want to understand is whether, if I engage the WOF switch, should I be able to measure a current at the solenoid?
Thanks
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Mar 2002
Posts: 13,657
Likes: 616
From: Phoenix AZ
Yes you you should be able to measure the solenoid current when operating. Connect wiring for a remote switch to the throttle connection point so you can operate a WOT/Kick-Down switch and monitor the current remotely. This also takes out the uncertainty of whether the pedal is operating the switch... evaluate.
Alan
Alan
Burning Brakes
Joined: Mar 2013
Posts: 1,018
Likes: 219
From: Sunshine Coast, QLD,Australia
Yes you you should be able to measure the solenoid current when operating. Connect wiring for a remote switch to the throttle connection point so you can operate a WOT/Kick-Down switch and monitor the current remotely. This also takes out the uncertainty of whether the pedal is operating the switch... evaluate.
Alan
Alan
Instructor
Joined: May 2023
Posts: 103
Likes: 68
From: Midlands UK
Still having issues with my 83 not changing up. I think I have the cable now adjusted fairly spot on.
Thinking outside the box, would I get the issue of not changing up unless i slightly back off the gas pedal if either the kick down switch or relay were faulty? 🤔
Thinking outside the box, would I get the issue of not changing up unless i slightly back off the gas pedal if either the kick down switch or relay were faulty? 🤔
