Read a dropping voltage from the throttle position sensor

Tiny
PAULHOMERJR
  • MEMBER
  • 1994 OLDSMOBILE BRAVADA
  • 146,000 MILES
What could be causing an analyzer to read a dropping voltage from the throttle position sensor as the RPM increases? I have replaced the TPS three times and the PCM yet the analyzer still continues to say the TPS is bad and shows the voltage dropping as I increase the RPM. It doesn't shift until above 2500 RPM and then shifts very hard. It also is running 200 RPM faster than normal at highway speeds even though it is in OD.
Monday, July 16th, 2012 AT 5:57 PM

12 Replies

Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
What code is comming up?
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Monday, July 16th, 2012 AT 6:01 PM
Tiny
PAULHOMERJR
  • MEMBER
  • 6 POSTS
22 TPS Sensor Low
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Monday, July 16th, 2012 AT 6:32 PM
Tiny
DOCFIXIT
  • MECHANIC
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Will need a DVOM see diagrams back probe TPS connector Black lead on bottom sensor ground and middle one RED probe. Key on at idle voltage less than 1 volt(.5 v best). Then operate throttle from idle to full meter should go up steady to 4.5 V
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Monday, July 16th, 2012 AT 6:43 PM
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Opps
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Monday, July 16th, 2012 AT 6:44 PM
Tiny
PAULHOMERJR
  • MEMBER
  • 6 POSTS
It starts out at.27 and drops as the throttle is opened.
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Monday, July 16th, 2012 AT 6:54 PM
Tiny
DOCFIXIT
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Check reference voltag must be 5V
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Monday, July 16th, 2012 AT 7:03 PM
Tiny
PAULHOMERJR
  • MEMBER
  • 6 POSTS
Reference voltage is 5.02. Checked the ground and it's fine also. The low voltage has been the same for all 3 new TPS.
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Monday, July 16th, 2012 AT 7:45 PM
Tiny
DOCFIXIT
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Makes no sence if have 5v REF all TPS is a variable resistor so you say at idle.27v and as open throttl goes to zero
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Monday, July 16th, 2012 AT 7:52 PM
Tiny
PAULHOMERJR
  • MEMBER
  • 6 POSTS
My point exactly. Could this be an issue with one of the tranny sensors?
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Monday, July 16th, 2012 AT 8:00 PM
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Unplug tps use jumper wire from 5v ref and then jumper ground on bottom wire hook up meter across ground and TPS signal open throttle what does it do?
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Monday, July 16th, 2012 AT 8:35 PM
Tiny
PAULHOMERJR
  • MEMBER
  • 6 POSTS
I figured out the problem. I bought the vehicle used and the engine had been replaced before I got it. The EFI was off of a 93 S-10 Blazer. Although the TPS looked the same, the throttle operates in the opposite direction. It took some research at the parts store but we got the right part and everything's perfect now. Thanks for your help. Have a great day.
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Wednesday, July 18th, 2012 AT 9:19 PM
Tiny
DOCFIXIT
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Well don't that beat all and explains the weird readings
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Thursday, July 19th, 2012 AT 7:40 PM

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