Help! Trans codes galore !

Kfnvhi

Member
Just purchased my first Tahoe, 2005 Z71. Everything was working perfectly until I installed a flashing blue LED fake security light in the dashboard. I tapped the two wires for the LED into the fuse box on the side of the dashboard. The LED was working fine, but now either coincidentally or as a result of what I did the check engine light is on and the transmission is in limp in. PO codes 758 740 753 785 2761 are coming up. I did check all the fuses I could find and everything seems good. Could this be something I did in the fuse box or is it just something like a bad ignition switch?
 

Locksmith

Well-Known Member
I bought an 03 Envoy SLE for $850 with 186000 on the odometer, and this money pit has cost me in parts, approximately two grand! Welcome to my world! Disconnect the wires, clear the codes and go from there! Whoever mated a car engine with a computer should be shot!
 
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Kfnvhi

Member
Thanks. Already disconnected everything. Cleared codes. Even left battery disconnected overnight. Codes came right back. From everything I read, if it has multiple codes like this it most likely is an electrical glitch not a failure of the transmission. But it certainly could stem from a bad ignition switch from what I read.
 

Mooseman

Moderator
Definitely a wiring or power issue. The main plug and wiring to the tranny would be suspect as well as the internal wiring. Could also be a ground. Ignition switch would usually have other weirdness associated to it but it's a possibility.
 

Reprise

Lifetime VIP Supporter
https://www.google.com/url?sa=t&source=web&rct=j&url=#&ved=0ahUKEwid8eWLmezXAhWMzIMKHWGtBYgQwqsBCCgwAA&usg=AOvVaw0VTJzWxrN8ZFOD4xbU2nov
(On edit: If the link doesn't resolve, just paste your sentence with the codes into google - you should find a video by May03LT as one of the first links - that's how I found it.)

The above link should help a bit; it's for a TB, not a Tahoe, but the concepts are the same. It was created by one of our more knowledgeable members.

Note that the fuse # referenced (47) may be different on your vehicle, or in a different location. Underhood, #47 is a relay on the TB, the fuse # 47 is in the auxiliary box under the 2nd row seat.

I believe #47 is called IGN 0 ; it's a 10A
After watching the video, check the corresponding one in the tahoe.

Both vehicles of that year share the same transmission (4l60e), so there's a good chance the circuitry mentioned above is similar. Note - I'm *not* pointing toward your trans as the issue. All of the sensors related to your codes are fed by the same circuit, which the video explains, so it's likely to be fuse or wiring related.
 
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Kfnvhi

Member
Thanks! You we’re dead on. Just posted that I got it fixed. Found that ign o Fuse not making good connection. I appreciate your in depth response
 

billybowlegs

New Member
I'm having this same issue in an '02 Tahoe. P0740, P0753, P0758, P0785, and P1860. I tested/replaced all the IGN-related fuses (none were blown, but I like to attack the cheapest option first just in case). I also replaced the ignition switch on rec from autozone folks, before I had a chance to really research the issue. I watched the video linked above and I have power on both sides of the IGN 0 fuse with the key in run.

What's next, just trace all the wires from the trans back through the PCM, etc.? During a recent move, I had to leave the car sitting for about a month. I did see some rodent teeth marks in a rubber piece of trim, so I'm wondering if they didn't chew some wire up somewhere along that circuit.
 

Mooseman

Moderator
More than likely something with the wiring to the tranny. since you have evidence of a rodent infestation, the possibility is high. Check in and under the fuse box as I have read one thread where a bad connection there caused the same codes. If you want to read up:
https://www.google.ca/search?newwindow=1&source=hp&ei=iJFeWpLqKYLJjwTh85vQBQ&q=P0740,+P0753,+P0758,+P0785,+and+P1860+site:gmtnation.com&oq=P0740,+P0753,+P0758,+P0785,+and+P1860+site:gmtnation.com&gs_l=psy-ab.3...2860.11718.0.12329.21.20.0.0.0.0.292.2167.10j6j2.18.0....0...1c.1.64.psy-ab..3.2.416.0..0i22i30k1.0.he3e7_tCGSc
 
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Kfnvhi

Member
Just a note on the “IGN O” fuse.... my symptoms were the same but my tests showed power on both sides of that fuse also. It just wasn’t enough of a good connection. I took out the fuse and pushed the socket pins closer together and also put a tiny twist in the two fuse pins to make it fit real tight. Might be a good idea to try that first since its easy.
 

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