Thermador PGR364GDZS LED code 21. New potentiometer didn't fix

[naftaturbo]

Thermador PGR364GDZS oven stopped functioning.  LED blink code is 21 which I found crosses to E5, indicates oven potentiometer failure (also known as temperature switch).  I tested the potentiometer with a cheapy VOM and indicated Pot was bad - didn't match resistance specs.  Replaced Pot with a new 624610.  Did NOT fix the problem.  I then took back my Fluke 75 which I'd lent out and used that to measure both pots.  New Pot (and old Pot after I dismantled and cleaned with eraser and contact cleaner) match Thermador's values found in their "Professional Series Cooktop and Range Training Program" PowerPoint presentation:

Between red/white (pins 2/1) I get nearly perfect nominal values for Off position, 140° (3.64 kOhm), 350° (20.89 kOhm), 450° (29.48 kOhm), Broil detent (38 kOhm), clean detent (45.5 kOhm), however the last line in Thermador slide repeats Off position(invalid cook temp) specifying greater than 50 kOhm but I get 1.6 Ohm.

Between red/black (pins 2/3) I get essentially the inverse of values between red/white except that Off position I get 49.7 kOhm.

Between black/white (pins 3/1) I get 49.8 kOhm at every position.

The values are nearly the same for all three color/pin pairs for the new Pot and the original one (after I cleaned it out) .

I'd really appreciate receiving suggestions for what my next step should be.  We've been without an oven for nearly 5 days and my wife is beginning to get a bit agitated (plus she's making me use the outdoor grill a lot...

[naftaturbo]

Since it appeared that both potentiometers were working correctly (that is, the resistances were within the expected band at each setting, and since there was no activity when I turned on the selector switch  and the potentiometer (neither blue light coming on, no relay clicking...) I decided to pull off the back panel and have a look at the DSI.  I disconnected the existing bake DSI (Gasliter.com 5574-7808, which I installed when the original failed a few years back) and tried a Fenwal 35-725903-997 that I had purchased a few years ago having been told that it would work for the broilers (it didn't).  With the Fenwal DSI connected the oven system started operating (sort of).  The two blue LED come on when the selector switch and potentiometer are turned on and the ignition process runs successfully; however once ignited the gas control solenoid isn't held on so flame turns off.  This I know to be due to the Fenwal DSI not being correct for my range.  I then connected the Gasliter.com that had been working and the oven came back to life.  Ignition process successful and gas control solenoid remains on.

So, even though the Thermador diagnostic code (LED: 21 > E5) states Potentiometer Failure - replace; that is not an accurate diagnostic. If I'd had my Fluke multimeter initially (note to self: no more lending critical tools) I would have seen the the original potentiometer was fine after I dismantled and cleaned it.  I could have saved myself the cost ($70) of a new potentiometer, and I would have sooner gone after the DSI and found that problem.  What I'm not sure of now is why the DSI all of a sudden stopped working.  After testing the Fenwal DSI and proving to myself that the potentiometer, control board, etc were good, I put back the Gasliter.com DSI and the unit continued to work for nearly a dozen trial oven on/off  trials.

I had an unused Gasliter.com 5574-7808 (I don't remember why...) so I put that one in, buttoned up the back of the range and cleaned up the top-end and (knock-on-wood) the oven has been working.  My wife is reserving judgement until she's used it for a couple of weeks as to whether I really fixed it.

My conclusions (and I hope they're useful to some other DIY'er reading this forum:  *Don't knock-n-wood too much; it makes my head hurt,  *When it comes to diagnosing appliance problems I'm a bit of a block-head, * Thermador could do a better job of creating and making available to customers a good Diagnostic Tree, * Don't lend out critical tools (like a Fluke multimeter) as you never know when an appliance will stop working as your significant other is needing that appliance, *Assume your cheapy Harbor Freight multimeter is giving you a false negative and double check with a good tool.

I'd still love to hear from some of the masters on this forum as to what I could have done better, where I could have looked for more reliable Thermador diagnostic information, why the DSI would have stopped working and then started again after I cycled the oven using the Fenwal DSI.

Thanks,,,