Reduced engine power light on

Tiny
JOETRACYJOETRACY
  • MEMBER
  • 2004 CHEVROLET TRAILBLAZER
  • 4.2L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 220,000 MILES
I recently had this light come on and the engine dropped to an idle. Shut off and restarted and it ran fine. Scanned it and there were no codes. So, after a little research I replaced the throttle body, the MAP sensor, and the accelerator pedal. After all this and yesterday it started up and the reduced engine power light was on. Shut off and the engine would turn over but not start. After sitting all night, it started up and ran fine. Please help. What else can be causing this reduced engine power situation? Never know when it's going to happen except that it is becoming more frequent now. The only thing I thought of left would be the computer. Is this a possibility or please tell me what is causing it? I'm running out of money.
Tuesday, January 11th, 2022 AT 4:02 PM

5 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
It is possible that this is the PCM. However, what scanner are you using to try to get codes?

This light comes on and sets codes so there should be some, but it is possible that you need to check them when the light is on.

This issue is normally caused by a sensor or the PCM so we need to double check codes with a different scanner so that we can make sure we are not missing something.

https://www.2carpros.com/articles/reduced-power-limp-mode

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

The most likely causes of this are the throttle body, o2 sensors, throttle position sensor, and finally the PCM.

So, let's stop by a parts store and see if they can scan it and get any codes and we can go from there.

Thanks
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Wednesday, January 12th, 2022 AT 4:58 PM
Tiny
JOETRACYJOETRACY
  • MEMBER
  • 25 POSTS
Well, Oreilly's scanned it and darn I forgot the exact code, but it said large or major evap leak detected. Now the check engine light has been on for 2 or 3 years and always displayed this evap leak, but car continued to run fine. I, however, have replaced throttle body and map sensor and accelerator pedal. The only thing you mentioned I haven't replaced is o2 sensors and the computer. I will try to get it rescanned to see if it shows more info.
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Thursday, January 13th, 2022 AT 7:18 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. I agree that it is unlikely that an EVAP leak will cause the reduce power light, but it is possible. So, can you write down the code when you scan it again and then we can just make sure?

Then if it were me, I would remove the o2 sensors and take a look at them.

Then run through this guide to test them just to make sure we are not replacing them unnecessarily:

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

Some people would just rather replace them, but I like to test them so let me know what you find.

Thanks
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Thursday, January 13th, 2022 AT 4:26 PM
Tiny
JOETRACYJOETRACY
  • MEMBER
  • 25 POSTS
Thank you to all that helped me with this. I replaced the throttle body, or rather Oreilly's warrantied it out and it fired right up. I've put approximately 3 to 400 miles on it since without one single issue. I'm so happy. Thank you.
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Friday, July 8th, 2022 AT 11:16 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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KENNY K is one of our best! Use 2CarPros anytime, we are here to help. Please tell a friend.
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Sunday, July 10th, 2022 AT 12:42 PM

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