TPS or ECM?? code 21 help!!

[JayPeasy]

My ecm is putting out a code 21. Im getting around 5 volts out of both of my positive tps connector wires when the pigtail is unplugged, does my ecm need to be replaced? the shop manual says one of the wires is supposed to be WELL under 2.5 volts... Its a ccc em4e quadrajet, 1986 Monte Carlo base 305 vin H
Coming from the ecm you have a three prong connector. you have the ground wire, the 5 volt wire and the other wire thats supposed to be low voltage. mine "low voltage" wire says 4.777 when the plug isnt plugged into the carb. The manual says its supposed to be below 2.5 volts when unplugged.. How can i check this circuit, or the ecm? i tested for continuity across the tps plug, There were no wires shorted to each other. Should i get a new ECM? How do i make sure the new one doesn't fail?? Help!

 

[DoubleV]

Can't answer your question. If you have an actual GM service manual, it should have a flowchart that tells you what you need to check/do. If you you not have an actual GM service manual for your car, then you REALLY need to get one as the type of information you seek is not generally known to most.

I can tell you I once had a code 21 and it went away after replacing the TPS.

 

[Jshock]

Well I hope these diagrams help. Keep me posted and ill try and get you some more information
-josh

 

[JayPeasy]

I have the service manual, and those pages are in the manual. They pretty much say if the voltage is above 2.5v on that wire somethings wrong with the wiring or dcm. I tested the wiring for crossed wires/continuity and got nothing. thats pretty much all the m annual said to do, and est for an open circuit.. im not sure, but if its getting volts, its not open correct? Can anybody tell by those schematics what else to test? Im not a whiz when it comes to resistors and stuff like that lol... Thanks guys for your input. I ordered a used ecm off of ebay today to give a try, 40 bucks.. hope it works! id just like to know how to test the wiring before hooking up the ecm cuz i dont wanna burn it up... Thanks again guys!!

 

[rangertom]

Code 21 in my code scanner manual is for TPS... it says " Signal voltage is high during engine idle or deceleration.

 

[Jshock]

Sounds like if you have voltage and its sitting high at around 5 volts the. The Tps is bad. One more option you could try is hooking up your meter inline (series) with the Tps and manually operate it watching vtage. If the sweep is nice stray increasing voltage up to 5 volts at wide open and almost 0volts at shut it could be PCM. I would almost go for the tps in the first place. In my 6 years as an auto tech I've only seen one computer to be bad.

 

[JayPeasy]

but... im getting 5 volts on both the pos. lines when the plug isnt even plugged in to the TPS! even after a reset, and never plugging the TPS in before testing..

 

[Jshock]

I get that. The flow chart states that if voltage is above 2.5 unplug And jump the B and C terminals on the harness side and remeasure voltage. If its above 2.5 then you have a PCM problem. So what's the voltage measure when those terminals are jumpered together?

 

[JayPeasy]

I knew somebody would be able to read that chart better than me! Lol I thought it wanted me to measure the voltage between b and c haha.. Well I jumped b and c this morning And measured the voltage, still higher than 5.. I tested multiple times just to make sure my connections were tight. 5.03v Thanks for the advice, you were right, I was measuring wrong. :idea:

 

[Jshock]

No problem. Sorry it's a PCM issue that sucks. I used to have an 83 camaro that flashed that code. It was a doozy because after a new PCM, new tps, and new wiring from the two it wouldn't go away. Turns out the chip I was using was causing a fault.