Weird throttle pedal and throttle body behavior
Thread Starter
Teching In
Joined: Aug 2014
Posts: 19
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From: Florida
Weird throttle pedal and throttle body behavior Hey everyone. So this issue has me ripping my hair out right now as well as giving me a massive headache trying to figure out what's going on.
Has anyone here ever experienced a throttle body that opens and closes just fine with pedal movement while the engine is off, but completely ignores pedal position when the engine is running? VCM scanner with engine off shows pedal position and TPS percentage both moving in relation to each other (though pedal position goes to 160% at WOT for some reason). Yet when the engine is idling, the TPS stays at its idle position even as the pedal position percentage is shown moving with pedal actuation. On first start, I have no codes and it idles perfectly but completely ignores pedal movement. But if I shut the engine off and restart, it struggles to idle for a few seconds then stalls and throws a P2135. If I clear the code and restart, it idles fine once again but still without throttle response, shut down, restart, stalls, sets code, etc...
Yet through all of that, if I move the pedal between restarts the TB blade moves just fine. It's only ignored and doesn't command the TB with the engine running.
This is a swap project with an LQ4 out of a 2003 Yukon XL Denali. I've got a PCM out of a 2006 Silverado 2500 HD with OS 12587811. And a matched pedal and TAC from a 2006 Silverado 1500. TB is the stock unit from the Yukon but all my research shows this TB was shared across all DBW 5.3s and 6.0s from 2003 to 2006 so this should work with the 2006 components correct? If I try to go buy a TB online for a 2006 2500 HD, the part number is exactly the same as what I currently have installed.
I have checked the 5v reference and low ref pins going to the pedal from the TAC with ignition on and those are good. Motor voltage at the TB connector is good when first turning the ignition on. TPS 5v and low ref at the TB connector is good. Motor windings in the TB checked ok at 3.2 ohms pin to pin. I have no idea what kind of resistance the TPS sensors on the TB are supposed to be at so don't have measurements for those.
I hooked the pedal up to a 5v supply and watched the voltage readings. Completely off of the pedal, the voltage for APP 1 is 0.93v and at WOT it's 3.99v. APP 2 was at 0.93v off the pedal, and 4.25v at WOT. From what I found online, these readings are a little high. Especially APP 2 at WOT. The test i found stated it was supposed to be a set 4v at WOT and I'm 0.25v higher. I have no clue if this will cause my issue though.
I'm just hoping someone can chime in here and let me know what they think could be going on. I would like to avoid a parts cannon mentality if possible. I'm leaning toward a bad TAC module right now but I just don't understand how it commands the TB fine with the engine off but loses all command of it with engine running while inconsistently setting a P2135.
Any insight here would be greatly appreciated! HPT VCM Scanner log of pedal vs TPS command with a restart and stall attached for your viewing pleasure.
Thanks all!
P.s. for clarity;
I didn't have this command issue with the engine's original PCM and TAC with a pedal from a 2004 Silverado. But I was struggling with issues of the TB going WOT at 60% pedal position which made it a chore to drive due to pedal sensitivity. I killed that PCM due to a short from a cut wire I hadn't noticed so figured in hopes of curing the sensitive throttle issue, I would just swap everything but the TB out for '06 parts since the '06 plastic pedal fits in my swap better anyway. Unfortunately, this plan has gone sideways as stated above. When swapping the PCMs, I decided to keep the '06 OS and just copy over all the calibration changes from the tune I was running on the original PCM. Nothing in the electronic throttle area was changed though. I kept all of those settings just how they were from factory for the '06 PCM in hopes of keeping perfect calibration between the PCM, TAC, and pedal now that they were all matched unlike before.
Has anyone here ever experienced a throttle body that opens and closes just fine with pedal movement while the engine is off, but completely ignores pedal position when the engine is running? VCM scanner with engine off shows pedal position and TPS percentage both moving in relation to each other (though pedal position goes to 160% at WOT for some reason). Yet when the engine is idling, the TPS stays at its idle position even as the pedal position percentage is shown moving with pedal actuation. On first start, I have no codes and it idles perfectly but completely ignores pedal movement. But if I shut the engine off and restart, it struggles to idle for a few seconds then stalls and throws a P2135. If I clear the code and restart, it idles fine once again but still without throttle response, shut down, restart, stalls, sets code, etc...
Yet through all of that, if I move the pedal between restarts the TB blade moves just fine. It's only ignored and doesn't command the TB with the engine running.
This is a swap project with an LQ4 out of a 2003 Yukon XL Denali. I've got a PCM out of a 2006 Silverado 2500 HD with OS 12587811. And a matched pedal and TAC from a 2006 Silverado 1500. TB is the stock unit from the Yukon but all my research shows this TB was shared across all DBW 5.3s and 6.0s from 2003 to 2006 so this should work with the 2006 components correct? If I try to go buy a TB online for a 2006 2500 HD, the part number is exactly the same as what I currently have installed.
I have checked the 5v reference and low ref pins going to the pedal from the TAC with ignition on and those are good. Motor voltage at the TB connector is good when first turning the ignition on. TPS 5v and low ref at the TB connector is good. Motor windings in the TB checked ok at 3.2 ohms pin to pin. I have no idea what kind of resistance the TPS sensors on the TB are supposed to be at so don't have measurements for those.
I hooked the pedal up to a 5v supply and watched the voltage readings. Completely off of the pedal, the voltage for APP 1 is 0.93v and at WOT it's 3.99v. APP 2 was at 0.93v off the pedal, and 4.25v at WOT. From what I found online, these readings are a little high. Especially APP 2 at WOT. The test i found stated it was supposed to be a set 4v at WOT and I'm 0.25v higher. I have no clue if this will cause my issue though.
I'm just hoping someone can chime in here and let me know what they think could be going on. I would like to avoid a parts cannon mentality if possible. I'm leaning toward a bad TAC module right now but I just don't understand how it commands the TB fine with the engine off but loses all command of it with engine running while inconsistently setting a P2135.
Any insight here would be greatly appreciated! HPT VCM Scanner log of pedal vs TPS command with a restart and stall attached for your viewing pleasure.
Thanks all!
P.s. for clarity;
I didn't have this command issue with the engine's original PCM and TAC with a pedal from a 2004 Silverado. But I was struggling with issues of the TB going WOT at 60% pedal position which made it a chore to drive due to pedal sensitivity. I killed that PCM due to a short from a cut wire I hadn't noticed so figured in hopes of curing the sensitive throttle issue, I would just swap everything but the TB out for '06 parts since the '06 plastic pedal fits in my swap better anyway. Unfortunately, this plan has gone sideways as stated above. When swapping the PCMs, I decided to keep the '06 OS and just copy over all the calibration changes from the tune I was running on the original PCM. Nothing in the electronic throttle area was changed though. I kept all of those settings just how they were from factory for the '06 PCM in hopes of keeping perfect calibration between the PCM, TAC, and pedal now that they were all matched unlike before.