Will I'm just about tired of my TB. Every since I've had it it's been one thing after another. Had to get me trans and transfer case, new interior wiring harness. Vent actuators of various types, etc etc etc. Now this shit happens. I guess it started some time back when I was running on fumes and REP light came on. Pulled over for some fuel and everything was fine. Few months later it starts again. First just once in a blue moon. I thought it was loose battery cable so I got it fixed. Then it started happening all the time. Until now it seems barely drivable. I took it to AutoZone got a p0121 code they recommended getting new throttle body. Well first I decided to clean throttle body and it seemed better only one or two times every half hour. Then today it's back to once every five minutes. Sometimes it won't let it go out of second gear and will Rev to my heart's content and other times it seems like I am only lightly pressing gas when I'm flooring it. The only temp fix that works for me is to pull over, shut truck off, start back up and run ten minutes then restart and go. That seems to work 90% of the time. But for how long can very from seconds to the rest of the day. I have noticed it at all speeds, temps, on start up and while driving. There's no method to the madness!! I lost my f#@$ing job over this thing and I am at a total loss. I checked connections at throttle body wiggling wires and such and couldn't get light to come on. Same deal at gas pedal. Going to try to check grounds under the hood now. Any help much obliged. Or if you have a running driving vehicle for trade near harrodsburg KY let me know I'm sick of this thing. I've always loved Chevy's but this may be last straw!
Reduced engine power P0121 Help me!!!!
- Thread starter kyBoy04tblt
- Start date
Mooseman
Moderator
P0121 is a throttle position sensor error, aka: gas pedal sensor. Replace that and clear the codes.
Well little update I read some where you can drive with fan unplugged for a time and it didn't work.
Thanks mooseman so you are saying I need a gas pedal assy then and just clear codes?
Thanks mooseman so you are saying I need a gas pedal assy then and just clear codes?
Mooseman
Moderator
Yup unless it`s a wiring issue there but the code points to a faulty pedal sensor.
Thanks again, Auto zone said I needed new tps sensor aka new throttle body. Do you think unplugging gas pedal sensor and cleaning contacts help out is a replacement the only fix?
AtlWrk
Member
- Dec 6, 2011
- 674
Whoah! No. The throttle position sensor is in the throttle body, not the gas pedal.
The gas pedal is the Accelerator Pedal Position (APP) sensor and not indicated by this DTC.
90% of the time it's a wiring issue and not a fault with the throttle body sensors themselves. The two usual suspects are the fan clutch harness or the wiring at the throttle body connector. This particular code points specifically to the sensor A signal wire (dark green) but could be the voltage reference wires too. I know you've wiggled the harness trying to replicate the fault but it may be more subtle than that. Did you do this with the fan harness, too? Remove the connector from the throttle body and make sure all of the terminals are fully seated (push the wires in the back). Inspect for corrosion or damage (a good electrical contact cleaner or MAF spray is recommended). Pull back the harness wrap/tape by the connector and look really, really closely at each individual wire for kinks, cracks, flimsiness--anything that might indicate a broken conductor inside. When reinstalling make sure the plug is really, fully seated on the throttle body connector before pushing in the gray CPA (Connector Position Assurance) clip--I got burned by this once.
Only after all that would I consider replacing the throttle body itself.
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I was assuming it could be a problem with communication from the APP to the TPS but it makes more sense what your saying. I tried wiggling and such on the fan wiring connector as well to no avail.
Going to inspect wiring and do another tug test now.
Thanks for all the help guys. Any issues I've had that had me dumbfounded
I've always been able to turn to this great forum for guidance.
Well did the I'll wiggle and nothing. Then I checked the wiring around harness and no frays, tears etc. I noticed that a couple of wires on the TB harness clicked when I pushed in on em. Saying a prayer and off on a test run.
Well did the I'll wiggle and nothing. Then I checked the wiring around harness and no frays, tears etc. I noticed that a couple of wires on the TB harness clicked when I pushed in on em. Saying a prayer and off on a test run.
Nevermind truck started with my dear old pal the REP light shining brightly so that didn't work.
AtlWrk
Member
- Dec 6, 2011
- 674
Bummer. Well, you have a couple options now:
1. Replace the throttle body (either new or from a junkyard depending on what's available and $$). A used one is fine because the odds you get another bad one are extremely low.
2. Do you have a friend with a trailblazer or Envoy that would let you swap throttle bodies just to check?
3. Continue trying to diagnose the problem by using a multimeter/DMM/DVM to probe for continuity and voltages on various wires. Do you have one and are familiar with how to use it?
1. Replace the throttle body (either new or from a junkyard depending on what's available and $$). A used one is fine because the odds you get another bad one are extremely low.
2. Do you have a friend with a trailblazer or Envoy that would let you swap throttle bodies just to check?
3. Continue trying to diagnose the problem by using a multimeter/DMM/DVM to probe for continuity and voltages on various wires. Do you have one and are familiar with how to use it?
Well here I am broke down on a back road. I'm guessing I need to start hunting a cheap throttle body this thing is killing me. Why can't you just purchase TPS sensor separately? I seen one for a v8 TB why not the 4.2?
AtlWrk
Member
- Dec 6, 2011
- 674
Frustrating for sure. The sensor on the 5.3L TB is in a housing that clips onto the throttle body and basically plugs in making it DIY friendly.
On the 4.2L, the sensor housing/cover is stamped to the throttle body, has welded contacts inside, and the sensor arm itself is welded to the shaft. It's far more integrated to the throttle body instead of just being something attached to it. I've taken one apart and I can attest that it's a major pain in the a$$, and pretty much impossible to get back together.
Why the difference? No clue.
I can't guarantee a new throttle body will fix your problem either. But without being to dive into the wiring it's a logical next step.
On the 4.2L, the sensor housing/cover is stamped to the throttle body, has welded contacts inside, and the sensor arm itself is welded to the shaft. It's far more integrated to the throttle body instead of just being something attached to it. I've taken one apart and I can attest that it's a major pain in the a$$, and pretty much impossible to get back together.
Why the difference? No clue.
I can't guarantee a new throttle body will fix your problem either. But without being to dive into the wiring it's a logical next step.
That figures I don't have a DMM but I could get one I'm sure there's a how to on the procedure. I guess I have until Friday to find a cheap throttle body. Thanks again guys for the help.
A little update, got my new to me throttle body installed and after a short ride maybe ten minutes down the road, it happens again. The reduced engine power light comes back on. I didn't reset codes except by removing battery cable for thirty minutes while removing and reinstalling new throttle body. Any suggestions out there? Looks like I'm going for the app sensor next. Maybe mooseman was right.
Mooseman
Moderator
I just hope I can putt putt the 40 min drive to my new job in morn be there by 8 leave about 6 30. Hopefully I can find a cheap had pedal tomorrow.
Well little update I got my truck in a shop and they switched for a new throttle body and pedal pressure sensor. Drove up found out I had a transmission fluid leak and about ten minutes after they closed (my luck) rep light on again.So now I'm thinking maybe a wiring issue what should I tell the shop to do? Any help much obliged.
What you are facing is "The Problem of a Three Legged Stool":
Leg #1 = The Throttle Body & Harness Connections
Leg #2 = The Accelerator Pedal & Harness Connections
Leg #3 = The Mass Air Flow Sensor & Harness Connections
Snap off any one or any combination of these Legs and the Stool Falls Down. Right now... My money is on a Problem with the Electrical Wiring Harness at the MAF. The problem with a sketchy wire in this First Place To Register Data to the PCM is that the MAF actually works by Weighing the In-Coming Air... courtesy of having the IAT right there as well to ensure that the PCM can calculate the Air Weight based upon what the Density-vs-Temperature turns out to be. If you have any or all of the wires associated with the MAF Sensor cut, pulled out, over-stretched, damages of losing contact for any reason... The PCM will throw a Reduced Engine Power Code and light up the Dashboard...without actually telling you WHICH of the Three Legs of the Stool is misbehaving.
FWIW... Wire Trace each and every wire in the MAF Harness. Since the other contributing members in this thread have already suggested the wiring and connections as central to the problem... If you find ANY problem there... then purchasing a New MAF OEM quality connector with LONG Leads and soldering-shrink-wrapping in the longest lengths you can buy as a replacement for what might just be the culprit would be the next place to investigate. Here are some choices available for this Connector. Caveat Emptor: Don't Go Cheap on THIS Item:
http://www.rockauto.com/en/catalog/...onnector,mass+air+flow+sensor+connector,10183
Leg #1 = The Throttle Body & Harness Connections
Leg #2 = The Accelerator Pedal & Harness Connections
Leg #3 = The Mass Air Flow Sensor & Harness Connections
Snap off any one or any combination of these Legs and the Stool Falls Down. Right now... My money is on a Problem with the Electrical Wiring Harness at the MAF. The problem with a sketchy wire in this First Place To Register Data to the PCM is that the MAF actually works by Weighing the In-Coming Air... courtesy of having the IAT right there as well to ensure that the PCM can calculate the Air Weight based upon what the Density-vs-Temperature turns out to be. If you have any or all of the wires associated with the MAF Sensor cut, pulled out, over-stretched, damages of losing contact for any reason... The PCM will throw a Reduced Engine Power Code and light up the Dashboard...without actually telling you WHICH of the Three Legs of the Stool is misbehaving.
FWIW... Wire Trace each and every wire in the MAF Harness. Since the other contributing members in this thread have already suggested the wiring and connections as central to the problem... If you find ANY problem there... then purchasing a New MAF OEM quality connector with LONG Leads and soldering-shrink-wrapping in the longest lengths you can buy as a replacement for what might just be the culprit would be the next place to investigate. Here are some choices available for this Connector. Caveat Emptor: Don't Go Cheap on THIS Item:
http://www.rockauto.com/en/catalog/...onnector,mass+air+flow+sensor+connector,10183
So maybe invest or borrow a DMM and test wires from throttle body and so sensor and maf sensor. This truck is killing me.
Before you pursue any further diagnosis... I'd like to recommend that you look over this Youtube Two Part Series on investigating The Problem of Reduced Engine Power on a GM Truck that initially follows a protracted path to a solution that closely matches what you might encounter after you follow what the VOP (Video Original Poster) does to run down a Broken MAF Sensor Wire problem that was causing these intermittent issues. Pay particular attention to Part Two:
In spite of the fact that the VOP is using a DMM and a High End Snap-On Verus Scanner for his diagnostic analysis...what he says to look for and graph for the average good quality Scanner can still be applied...and the fact that the vehicle involved is a Big Block GM V8 makes no difference whatsoever as to What and Why he does his work, The solution path can still be applied in your case with a Decent Scanner and a Good Daylight Viewable DMM :
Part One:
Part Two:
In spite of the fact that the VOP is using a DMM and a High End Snap-On Verus Scanner for his diagnostic analysis...what he says to look for and graph for the average good quality Scanner can still be applied...and the fact that the vehicle involved is a Big Block GM V8 makes no difference whatsoever as to What and Why he does his work, The solution path can still be applied in your case with a Decent Scanner and a Good Daylight Viewable DMM :
Part One:
Part Two:
