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BOBBYSS
BOBBYSS, Master Technician
Category: Chevy
Satisfied Customers: 17143
Experience:  ASE MASTER CERTIFIED, AA DEGREE AUTO/DIESEL TECH
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Chevrolet Tahoe LT: hal, i am having a similar problem

Customer Question

hal,
i am having a similar problem to one that you responded to a coup;e pf years ago. my 2004 chevy tahoe is throwing a u1000 code as well as lean bank 1 and 2 and random misfire. i think there is probably a connection problem or a ground but i dont really know where to look
Submitted: 1 year ago.
Category: Chevy
Expert:  BOBBYSS replied 1 year ago.
Hello, my name is Bobby. Thank you for the question. Can you tell me how the Tahoe is actually running besides the light being on?
Customer: replied 1 year ago.
the drivability issues are intermittent. it initially had the problem ver a year ago and then went away. we were on a long trip and by the time we got home the check engine light had went out and when i hooked up my diagnostic tool there were no codes present or stored. this time when the problem started again, it is still intermittent but in a different way. what happens is that you are driving along and everything is fine and then suddenly it is like you have lost control of the throttle body (this is a drive by wire throttle) because the throttle is totally unresponsive and the vehicle will go to a rough idle and most of the time it will stall. i say that it is intermittent because if you cycle the ignition a few times and start it a few times then eventually you can get the vehicle to start up and run fine for a few miles.
Customer: replied 1 year ago.
you may want to read the question and answer here http://my.justanswer.com/question/guest/1d317cc9651b48a8a62253f929a81511
this looks to be a similar issue, but there is not enough detail in the discussion for me to diagnose my issue
Expert:  BOBBYSS replied 1 year ago.
Thanks for getting back with me. Most of the time this is caused by a communication issue between modules. The lean codes may or may not be associated with the U1000 code. You need to check the connections at the PCM under the hood. It is common for there to be water intrusion and corrosion there. Clean this connection and add some dielectric grease. I would then check the ground connections on the front and rear of the cylinder heads. I have also seen a failure in the ignition switch cause this also.
Customer: replied 1 year ago.
i have already inspected the green and blue connectors on the pcm as well as all 6 connectors on the bcm and there was no obvious corrosion or gunk of any kind. i also inspected the grounds on the frame below the drivers feet and cleaned filed and deoxidized those ground straps. so far this has made no change in the problem.
Customer: replied 1 year ago.
i will clean and deoxidize the grounds on the heads in the morning
Customer: replied 1 year ago.
is there a way that i can diagnose the ignition switch?
Expert:  BOBBYSS replied 1 year ago.
You can do a voltage drop test of the switch. Remove the steering column covers and test the wires on the switch. You should have about 2-3 wires with battery voltage. The other should have none. Then turn the key to the run position and all but one should have full battery voltage.
Customer: replied 1 year ago.
i will do that as well. do you know which wires should have/not have voltage?
Expert:  BOBBYSS replied 1 year ago.
Red wire and red/white wire should have power with the key off. With the key in run all but the yellow wire should have battery voltage.
Customer: replied 1 year ago.
sweet, i will chk them. are the grounds on the rear of the heads hard to get to?
Customer: replied 1 year ago.
will you be available in the morning for more questions?
Customer: replied 1 year ago.
i have checked the ignition switch and it checks out fine. i also checked the ground straps and it seems on this engine that there are no ground straps on the heads, there is only one ground strap (braided) from the back of the block just above the transmission that runs up to the firewall.
Customer: replied 1 year ago.
more info,my harbor freight diagnostic tool has been unable to communicate with the vehicle since this issue started. i went to Autozone this morning and they have a Bosch scanner that did connect and it is the SRS module that is giving the u1000 code. there is also a code from the ABS module C0283 related to a traction switch circuit. these codes may not be directly linked to the drivability issues as my trip to Autozone was trouble free with the CES light off and there were no lean or random misfire codes present. i am curious if temperature could be related as it was over 100 degrees here yesterday and it was nice and cool this morning.
Expert:  BOBBYSS replied 1 year ago.
That is strange that it ran fine all of a sudden today. The other codes you are getting make me believe that you may have an issue with the communication lines between the modules. I am surprised though that you do not have any grounds. Most of the time there is one on the front of the passenger side head and one on the rear of the driver side head.
Customer: replied 1 year ago.
i may or may not have got it working by deoxidizing all of the connections at the PCM and the BCM but i am still concerned about not being able to communicate with the PCM using my scanner. we will just have to drive it for a while and see if it starts having the problem again. do you have any idea what wires i should check for continuity in order to determine if the connection between the SRS module and the PCM is good? also do you have any ideas for the C0283 code? do you know how i might troubleshoot a bad connection between the OBDII port and the PCM since my scanner wont communicate?
Customer: replied 1 year ago.
As for the grounds, I will double check the front of the passenger side head. I can see how someone could mistake the braided ground line that bolts to the back of the block for a ground line to the drivers side head, but using a mirror i was able to unmistakably determine that the ground is in fact bolted to the block just above the transmission bell housing on the drivers side.
Expert:  BOBBYSS replied 1 year ago.
If it is not communicating you are going to want to make sure that there is power getting to the data link connector. Or simply make sure that the CIG fuse is good in the fuse box under the hood.
Customer: replied 1 year ago.
i will check the fuse. it labeled CIG on the fuse map? i believe that the data link connector is getting power because the scanner powers up when you plug it in to the connector.
Expert:  BOBBYSS replied 1 year ago.
It will either be labelled CIG or LTR. Simply see if it is fine. If it is and there is still no communication then it may be a communication line issue or a module problem.
Customer: replied 1 year ago.
i checked all fuses under the hood and they are all good. what next?
Expert:  BOBBYSS replied 1 year ago.
Have you checked for power at the connector? If there is power then there is a PCM issue.
Customer: replied 1 year ago.
What pin do I probe for power?
Expert:  BOBBYSS replied 1 year ago.
When looking at the connector it is on the bottom right side.
Customer: replied 1 year ago.
i have power to the correct pin.
Expert:  BOBBYSS replied 1 year ago.
If you have power to the pin and if the scan tool is powering up, and if the scan tool works and will communicate with other vehicles then the PCM sounds like it is failing.
Customer: replied 1 year ago.
do i have to have this pcm remanned like some others that are vin coded or can i just get a matching one from the yard and install it?
Expert:  BOBBYSS replied 1 year ago.
Whether you have your PCM re-manufactured or install another used or new one it has to be programmed and VIN coded to your vehicle.
Customer: replied 1 year ago.
Is there any way to verify that the PCM is failing short of replacing it and seeing if it fixes the problem?
Expert:  BOBBYSS replied 1 year ago.
Since your scan tool will not communicate with it you do not have many options to test it.