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strange TPS wiring issues
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E30IS



Joined: 26 Jun 2008
Posts: 105

PostPosted: Thu May 14, 2015 1:34 am    Post subject: Reply with quote

How common is it for the signal wire on harness side to have 5V when there is no load on it (i.e. no sensor connected)? this is what GM alluded to earlier but i didnt pickup what he meant. it seems he was correct, what i thought was the 5V pin is the signal pin and the 5V ref pin is simply completely dead, this would explain why i get bugger all voltage range closed to WOT and why the voltages drift about 5% with temperature.

i guess i didnt expect one of the pins to be dead and to still have a functioning TPS albeit not a great signal

for example the OEM e36 bmw with Siemens ECU is like this, two of the pins have 5V, the signal and the 5V supply
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Matt Cramer



Joined: 25 Sep 2007
Posts: 395

PostPosted: Thu May 14, 2015 8:11 am    Post subject: Reply with quote

Some analog to digital converter circuits will "float high" when there is no applied load.
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E30IS



Joined: 26 Jun 2008
Posts: 105

PostPosted: Thu May 14, 2015 4:01 pm    Post subject: Reply with quote

Matt Cramer wrote:
Some analog to digital converter circuits will "float high" when there is no applied load.


do you have a good link to where this is discussed in detail?

with regard to original post i seem to have found the likely error with 5V supply. the plug and play harness appears to have been done incorrectly and the supply got routed to the incorrect pin of the OEM harness which happens to be the AFM (not used). i should be able to locate it pretty easily and see if that fixes the issue
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E30IS



Joined: 26 Jun 2008
Posts: 105

PostPosted: Fri May 15, 2015 1:38 am    Post subject: Reply with quote

well with the new found 5V supply the P&G sensor now works as per expected.

with voltage 0.8V closed to 4.8V open it should provide a better resolution than 0.9V closed to 2.15V which was how it has been
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joe90



Joined: 19 Mar 2013
Posts: 382
Location: under the car

PostPosted: Fri May 15, 2015 4:39 pm    Post subject: Reply with quote

E30IS wrote:
Matt Cramer wrote:
Some analog to digital converter circuits will "float high" when there is no applied load.


do you have a good link to where this is discussed in detail?



It's called a "pull up resistor".
eg. using a temp sensor.
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