installed cam,still throwing po121.help.!!
04-24-2005, 09:55 AM
#1
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installed cam,still throwing po121.help.!! last fall I had a bunch of mods done at livernois motorsports in detroit mich.had them install a 224/224 cam, headers,jantzer ported tb,390,gears,ect,had them tune it and since then I keep getting the po 121 code wich means a bad tps.but its not the tps because I changed it and it still keeps throwing it [had it deleted 3 times at aotozone] the thing is it runs great,and will throw the SES light while Im just cruising around,NOT AT WOT!.I think It has somthing to do with the cam and the idling,and Its throwing off the tps. any Ideas.? 
04-24-2005, 02:12 PM
#2
I have over the years working on GM cars came across this. The problem turned out to be the A/C high pressure switch mounted in the liquid line of the A/C system. It shares the 5 volt reference w/ the TPS & would intermittantly internally short itself out. This would cause the PCM to see low TPS voltage & flag a code. I'd say disconnect it & see if it is your problem.
hope it helps...
hope it helps...
04-24-2005, 05:47 PM
#3
Is the jantzer TB Drilled or just a solid plate???
P0121 is thrown when the MAP shows errors with what the pcm says it is supposed to be...
P0121 - TPS Performance
The VCM will calculate an expected TPS position in two MAP ranges. If the MAP is less than MinMAP then it will use one table to calculated expected TPS, if MAP is greater than MaxMAP it will use a different TPS calculation table. To disable this test set MinMAP to 0 and MaxMAP to 100.
(meaning this can be tuned out)
Stock setting for this test
P0121 Max MAP: 65
P0121 Min MAP: 55
if your TB is a solid Plate...it will see a different value than what it wants to see in the TPS vs MAP table...and Throw a code...
this also means it doesnt hurt anything...its just a code to make sure parts are working correctly
P0121 is thrown when the MAP shows errors with what the pcm says it is supposed to be...
P0121 - TPS Performance
The VCM will calculate an expected TPS position in two MAP ranges. If the MAP is less than MinMAP then it will use one table to calculated expected TPS, if MAP is greater than MaxMAP it will use a different TPS calculation table. To disable this test set MinMAP to 0 and MaxMAP to 100.
(meaning this can be tuned out)
Stock setting for this test
P0121 Max MAP: 65
P0121 Min MAP: 55
if your TB is a solid Plate...it will see a different value than what it wants to see in the TPS vs MAP table...and Throw a code...
this also means it doesnt hurt anything...its just a code to make sure parts are working correctly
07-02-2005, 02:41 PM
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Anyone know how I should go about replacing/disconnecting the A/C high pressure switch. I am having the same trouble getting the p0121. I was going to replace the tps, until I saw this thread.
07-03-2005, 12:45 AM
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