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2002 Chevy Trailblazer


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Tom7662
User

Oct 21, 2012, 7:55 AM

Post #1 of 18 (5552 views)
  post locked   2002 Chevy Trailblazer  

brother-in-law has a 2002 Chevy Trailblazer that starts and runs put has no power and won't go over 10 mph. Haven't gotten to see what the trouble codes are but was wondering if anyone has any ideas on where to start. Was told it might be a mass airflow sensor?


Discretesignals
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Oct 21, 2012, 8:04 AM

Post #2 of 18 (5536 views)
  post locked   Re: 2002 Chevy Trailblazer  

Find out what the trouble code numbers are. Write them down and let us know. Need as much diagnostic information as possible. Could be an electronic throttle control problem.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Oct 21, 2012, 8:06 AM)


Tom7662
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Oct 21, 2012, 2:14 PM

Post #3 of 18 (5498 views)
  post locked   Re: 2002 Chevy Trailblazer  

come up with code p1515


Hammer Time
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Oct 21, 2012, 2:24 PM

Post #4 of 18 (5492 views)
  post locked   Re: 2002 Chevy Trailblazer  

Yep, there is a problem with the "drive by wire" system. Likely will need a new throttle body but it needs to be investigated further.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom7662
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Oct 21, 2012, 2:28 PM

Post #5 of 18 (5488 views)
  post locked   Re: 2002 Chevy Trailblazer  

what needs to be done to investigate it further. Press the gas peadal to the florr and won't go over 2000 rpms in park


Hammer Time
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Oct 21, 2012, 2:31 PM

Post #6 of 18 (5484 views)
  post locked   Re: 2002 Chevy Trailblazer  

The freeze frame data needs to be analyzed thoroughly. The sensor outputs needs to be tested. Not anything you would be equipped to do.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom7662
User

Oct 21, 2012, 5:56 PM

Post #7 of 18 (5472 views)
  post locked   Re: 2002 Chevy Trailblazer  

So checking it with a volt meter to see if it has 5 volts to the sensor wouldn't be of any help.


Hammer Time
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Oct 21, 2012, 6:00 PM

Post #8 of 18 (5469 views)
  post locked   Re: 2002 Chevy Trailblazer  

No, it wouldn't. 5v is only the reference voltage and not the sensor signal.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom7662
User

Oct 21, 2012, 6:05 PM

Post #9 of 18 (5464 views)
  post locked   Re: 2002 Chevy Trailblazer  

So this won't work? The main and only item in the tool list is what is called an ohm volt meter. Once you have identified the TPS sensor, turn on the ignition, do not start the car, make sure the volt meter is on twelve volts DC. Locate the connector that goes from the ECM (engine control module) to the TPS. Once you find this disconnect it completely from the throttle position sensor. There are three prongs; the center prong is usually the negative connector.

Once this is done, take the volt meter and connect the negative side (usually the black wire) to the ground terminal on the battery. When this is done take the positive lead, (usually the red wire) and attach it to one of the other prongs. The volt meter should read five volts, if you are on the reference wire for the TPS. If it reads anything below five volts then you are on the signal wire and need to go to the other prong in the connector. If it reads nothing on the volt meter then you are on the negative connector. Once you locate the reference wire, and it reads five volts then you know that you are getting proper reference voltage to the TPS. Therefore you have just eliminated a faulty power feed to ECM.

The next step is to put connector back on the Throttle Position Sensor. Take the positive lead for the volt meter and put it to the signal wire in the back of the connector, this is known as back probing. Take the negative lead from the volt meter and put it to the center wire which is negative on the connector, take the butterfly shaft and turn it gradually and as you turn it you should get a gradual count upwards to five volts. If the volts fluctuate backwards or forwards then you know you have a faulty throttle position sensor


Hammer Time
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Oct 21, 2012, 6:11 PM

Post #10 of 18 (5460 views)
  post locked   Re: 2002 Chevy Trailblazer  

Yep, you have recited the basic testing procedure for testing a standard 3 wire TPS for a mechanical throttle system.

Unfortunately, that is not what your car is equipped with. You have an electronically controlled and operated throttle system that uses opposing TPS's internally with an electronic pedal position sensor inside the car and you couldn't open the throttle manually anyway.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom7662
User

Oct 21, 2012, 6:35 PM

Post #11 of 18 (5453 views)
  post locked   Re: 2002 Chevy Trailblazer  

Ok , i was just looking for a way of checking it . You seem to be very knowlegeable but haven't tried to explain how to check it other than stating that i am not equipped. What equipment would i need?


Hammer Time
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Oct 21, 2012, 6:37 PM

Post #12 of 18 (5449 views)
  post locked   Re: 2002 Chevy Trailblazer  

Let's start with a $5000 factory scan tool and $3000 lab scope and then throw in a few years of training to learn how to use them and know how the system actually works.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Oct 21, 2012, 6:40 PM)


Discretesignals
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Oct 21, 2012, 6:47 PM

Post #13 of 18 (5442 views)
  post locked   Re: 2002 Chevy Trailblazer  

According to the trouble code the PCM is seeing a different position percentage than what the PCM is commanding the throttle to be at. TPS and APP are redundant, so if it was a bad TPS or circuit issue is would be throwing a TPS code of some kind.

I would check to make sure the throttle isn't binding. You can do that by opening the throttle with your fingers with the ignition off and throttle motor connector unplugged. You have to remove the intake ducting. Feel for binding while opening the throttle blade. Had one a while back where the gears inside the throttle motor fell apart. If the throttle is binding or really hard to open, you have to replace the throttle body. When there is no power to the throttle motor the throttle will default to a semi open position.

Another possibility is the throttle bore is so gummed up it isn't allowing the throttle to be in the right position. With the engine running the PCM sees that the throttle isn't at the right position and force limits it. The simple fix is to clean the throttle bore and plate with throttle cleaner.

If the throttle plate isn't gummy or binding, needs more in depth diagnosis.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Tom7662
User

Oct 21, 2012, 6:48 PM

Post #14 of 18 (5438 views)
  post locked   Re: 2002 Chevy Trailblazer  

Thanks for your help.


Discretesignals
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Oct 21, 2012, 6:59 PM

Post #15 of 18 (5434 views)
  post locked   Re: 2002 Chevy Trailblazer  

Just to add: the throttle is spring loaded. Not enough to cut your fingers off. It shouldn't be flapping around with no spring pressure when you go to open it by hand to check for binding.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Oct 21, 2012, 7:00 PM)


Tom7662
User

Oct 22, 2012, 2:46 AM

Post #16 of 18 (5424 views)
  post locked   Re: 2002 Chevy Trailblazer  

Thank you very much, thats all i was looking for was a few ideas before he brought it in to a repair shop. Everyone on here is trying to save a buck whenever possible with the economy the way it is. It's people like you who are willing to help someone out why this site is so great. Thanks again


Tom7662
User

Nov 7, 2012, 6:01 AM

Post #17 of 18 (5350 views)
  post locked   Re: 2002 Chevy Trailblazer  

Just wanted to leave a follow up on this problem. Checked for binding and cleaned the throttlebody and still had the same problem.Ended up getting a used throttlebody and the vehical runs great now.Was told when the TPS sends wrong signal it will go into limp mode which would explain why it wouldn't go over 2000 rpms. Thanks


Tom Greenleaf
Ultimate Carjunky / Moderator
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Nov 7, 2012, 6:41 AM

Post #18 of 18 (5344 views)
  post locked   Re: 2002 Chevy Trailblazer  

Appreciate the followup and success. I'll lock thread as "fixed" and to prevent spamming. Can be re-opened upon request,

T






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