Used LS2 Throttle Body Junk? Feeling Scammed
Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 755
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Used LS2 Throttle Body Junk? Feeling Scammed
Long story short, about 3 months ago I purchased a used LS2 TB on here from a member that I won’t name. I’m just now getting around to mocking it up for install and am running into an issue I’m afraid was there all along. When I turn the ignition on (without starting the motor) I am able to press the gas pedal and hear my LS1 TB actuating. I attempted to perform this same check with the LS2 TB (and adapter harness) and I get zero TB movement accompanied by the “reduced engine power” DIC message. Pulling codes, they’re for throttle position sensors.
Am I missing something with my mock-up procedure or is the TB junk? I’m wondering if my test won’t work without some sort of PCM changes first.
Worst case, I have myself a nice $250 paper weight and will probably start a PayPal claim to try and get my money back...
Am I missing something with my mock-up procedure or is the TB junk? I’m wondering if my test won’t work without some sort of PCM changes first.
Worst case, I have myself a nice $250 paper weight and will probably start a PayPal claim to try and get my money back...
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,630
Likes: 4,076
From: Cape Coral, Florida
Do you have a scan tool where you can look at TPS voltage KOEO ??...TPS 1 is a “pull up” circuit design and TPS 2 is a “pull down”...if you can graph both voltages with the scan tool with key ON TPS 1 should go from maybe .7 to 3.9 volts and TPS 2 from 4.3 to a little over 1 volt at WOT...I’m just trying to remember from memory but you should never see 5 volts...the PCM is expecting to see certain voltages !!...if you don’t have a scan tool you can just backprobe both signal wires and read the voltages directly!!
Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 755
Likes: 272
Do you have a scan tool where you can look at TPS voltage KOEO ??...TPS 1 is a “pull up” circuit design and TPS 2 is a “pull down”...if you can graph both voltages with the scan tool with key ON TPS 1 should go from maybe .7 to 3.9 volts and TPS 2 from 4.3 to a little over 1 volt at WOT...I’m just trying to remember from memory but you should never see 5 volts...the PCM is expecting to see certain voltages !!...if you don’t have a scan tool you can just backprobe both signal wires and read the voltages directly!!
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,630
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From: Cape Coral, Florida
Well if you’re good with a DVOM with the TPS disconnected you have 2 each 3 wire potentiometers !!..2 each 5 volt references, 2 signal and 2 low reference (grounds)...i don’t know the wire colors off the top of my head but when you figure out the 5 volt ref. and ground the last 2 should be the signal...the signal wire with the lower voltage should be TPS 1 and the other should be TPS 2..,.record both TPS voltages at idle then at WOT...see what you have...I’ll look up what the PCM expects to see at both idle and WOT..,I’ll let you know !!...this is my video of a TPS Sweep” it’s called on my car but it’s with a scope and this is the BEST tool to graph the voltages for any glitches...scan tool and multimeter are just too slow...scope takes MILLIONS of voltage “samples” every second !!
Last edited by C5 Diag; Jul 27, 2019 at 06:13 PM.
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
The PCM doesn’t know what kind of TB you have installed...it just wants to see the voltages it was programmed for...TPS 1 at idle should be .13 to .67 volts and at WOT from 4.09 to 4.87. TPS 2 is 4.3 to 4.8 at idle and .13 to 1 volt at WOT !!...did you throw either a P1120 or P1220 with this TB installed ?????
Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 755
Likes: 272
The PCM doesn’t know what kind of TB you have installed...it just wants to see the voltages it was programmed for...TPS 1 at idle should be .13 to .67 volts and at WOT from 4.09 to 4.87. TPS 2 is 4.3 to 4.8 at idle and .13 to 1 volt at WOT !!...did you throw either a P1120 or P1220 with this TB installed ?????
As far as the codes, I erased them after the fact because I reconnected my LS1 TB and went for a drive. I neglected to write them down, but I’m pretty certain P1120 was one of them. I’ll be sure to note the specific codes when I make attempt #2 tomorrow. I’m sure they’ll come back
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,630
Likes: 4,076
From: Cape Coral, Florida
COOL !!...if the voltages aren’t right and you have those DTC’s you unfortunately have yourself a TB paperweight...I’ve seen other members trying to do this mod without much success !!... let us know what you find !!
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,630
Likes: 4,076
From: Cape Coral, Florida
Looking at TPS voltages for an LS2 the “normal” voltages on TPS 1 is 4.75 to .35 and TPS 2 is .35 to 4.65...COMPLETELY OPPOSITE of the LS1...LS2 TPS 1 is a “pull down”and 2 is a “pull up” !!....don’t know if that adapter switches the wiring to the LS2 TPS
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Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 755
Likes: 272
Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 755
Likes: 272
Great news! So upon testing signal voltages on the TB in an idle state (ignition on, motor off), I noticed both voltages were in the ballpark of where they were supposed to be, but slightly out of the expected range. This is what was causing the “reduced engine power” as it was not in the happy place. As I investigated further, I noticed at the initial turn of the key, the TB plate would judder as if it was trying to get to where it wanted, but wouldn’t make it. So I decided to manually articulate the TB plate and found that it would rotate from the static position to WOT just fine (and return smoothly/quickly), but when I tried to move the plate the reverse direction (which is what it does during startup) the TB plate contacted the bore and would get stuck. A quick loosening of the torx screws and minor adjustment of the TB plate allowed for smooth movement in all directions up to the end of travel. Plugged her back in for the test and all worked perfect! The TB calibrated as it should when ignition power was provided and moved in coordination with the gas pedal from idle to WOT.
Needles to say, I am relieved it was relatively simple to figure out/diagnose. Thank you to everyone who contributed info. It all helped with solving the problem!
Needles to say, I am relieved it was relatively simple to figure out/diagnose. Thank you to everyone who contributed info. It all helped with solving the problem!
