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06 3.5L P0121 and reduced power message.

  #1  
Old 04-28-2019, 11:25 PM
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Default 06 3.5L P0121 and reduced power message.

Looking for a little help here. Yesterday I had my check engine light come on, I stopped at autozone to have it checked. I was told it was P0121 and most likely my throttle body just needed to be cleaned or make sure the connections were all tight. That it was nothing serious. Tonight on my way home after driving a few hundred yards I stop at a stop sign and while stopped reduced engine power message popped up and it noticeably lost power as I tried to pull on to the shoulder. I turned it off and let it sit for a few and it started and drove fine. Any ideas what it might be or what to check?

Thanks,
Jonathan
 
  #2  
Old 05-02-2019, 12:53 PM
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Since then I havenít got the engine power reduced message, but the check engine light has stayed on. Ever since then Iíve had to give it gas each time to get it to started and it seemed weaker each time, but drove once started. It finally wouldnít start this morning. After serval tries I noticed a little bit of white smoke coming out near the passenger side headlight.

Is this where the throttle body is? Any help would be appreciated as to whatís wrong.
 
  #3  
Old 05-03-2019, 07:55 AM
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Just googled it and it looks like a TPS issue. Cleaning the TB wouldn't help that. Best way to further diagnose is to hook up a scan tool and see what the signal is doing. Upside is that it's a pretty simple circuit to diagnose and a cheap sensor if it is bad.
 
  #4  
Old 05-03-2019, 10:54 AM
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So it might just be the position sensor thatís bad and not the whole throttle control?
 
  #5  
Old 05-03-2019, 12:36 PM
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That's what I get for posting too early in the morning. Was thinking cable throttle for some reason. That's why cleaning the throttle made no sense since youd clearly feel it in your pedal if it was hanging up on carbon.

For electric throttle, I could see that being a possibility though as they're opening it with a tiny electric motor and you've got no physical connection to be able to feel it.

I found a nice list of troubleshooting online though:

Most common causes of this code:

  • Defective Throttle/Pedal Position Sensor or Switch
  • Dirty or carbon-filled Throttle Bore
  • Torn or jammed floor mats
  • Faulty or corroded Throttle/Pedal Position Sensor/Switch wiring or connections
They also had some nice troubleshooting info too:

When diagnosing a P0121 code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive while paying close attention to engine load, Mass Air Flow grams per second, RPM, and road speed on a data streaming scan tool. As you drive the vehicle, compare these values to the Throttle/Pedal Position Sensor PID or parameter ID. The Throttle/Pedal Position Sensor voltage values should rise and fall with changes in engine RPM and engine load.

Check the Throttle/Pedal Position Sensor connector with the key on-engine off. There needs to be a steady 5 volt reference voltage and an excellent ground. Find and use the proper engine performance wiring diagram to discern the proper color and position of these wires in the connector.

It is vital to do a key-on-engine-off performance test of the Throttle/Pedal Position Sensor by testing the Throttle Position/Pedal Position output from its signal wire. Typically, I operate the Throttle or Pedal manually and watch the rise and fall of its voltage or HTz on a lab scope to see if there are any sensor 'flat spots' or glitches. I test it again and watch the output on a data streaming scan tool to validate the sensor and Electronic Throttle Module(if equipped) connectivity with the PCM.
 

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