I have a 2005 C6 base model. Car sat for a month or so while having the A4 transmission rebuilt. Not even a day after getting it back the car went into reduced power mode, and threw throttle body codes P2135, 1505, & 1516. No accelerator pedal codes. I removed and cleaned throttle body, and checked/cleaned wiring harness and voltage. At cold startup, engine seems to have multiple misfires going on all at once and I get all the codes. I shut off and clear the codes. The car starts normally and will run, but only for a short time - 15 min or so - before either going into limp mode or stalling out with multiple misfires - I keep code reader hooked up so I can at least clear the codes and get out of traffic. Everyone says replace throttle body. The part is not an easy one to find, and new is quite costly. I have found a few throttle body's on car.parts.com., and eBay.

The questions I have are: 1 - Will a 2006 or 2007 work on a 2005? and 2 - can I put a ported replacement from a 2007 without having to get the car tuned?

 

Yes any GM silver blade will work. eBay is best for used and Mamo is the go to for ported units. No tuning needed as long as it’s GM.

 

First off who is "everyone" that says you need a new TB ??...I don't recognize the P1505 in Service Info but the P2135 is a TPS "correlation" DTC and the 1516 is a throttle actuator position performance one...trying to tie in your misfires and those DTC's it may be related to the Ignition 1 Relay 44...that relay powers the ETC (Electronic Throttle Control) Fuse 9 the TAC motor and also the injectors and coil packs...that fuse feeds Ignition 1 voltage circuit to the ECM...this maybe causing your misfires...try swapping Relay 44 with another 4 pin mini relay such as the defog relay...there may be high resistance across the load contacts of Relay 44...this is only a GUESS !!...now if this fixes it it's not the TB after all and you just wasted your money...you DON'T want to be a "parts changer"....what you can do is take a 12 volt test light connected to ground and probe one of the 2 test points on top of Fuse 9...ignition must be ON (green start switch light on)…the test light should be bright…BTW what voltages did you check and where ??

 

Keep in mind I'm a novice here, and really appreciate the help. I will get test light and try what you suggested. There is 5 volts coming from tps harness and I checked it for anything that could be loose. I did remove 44 and verify no ohm resistance between 87 and 30. It could still be bad - When I get home I will switch with another like relay and will let ya know. Thanks again!!

 

There are 2 separate 5 volt reference circuits feeding each TPS sensor…just checking for 5 volts doesn’t tell you much…you have to check the 2 signal wires…can your code reader look at each TPS voltage ??…TPS 1 is pulled up from low to high and TPS2 goes from a high voltage to low as the throttle goes from idle to WOT…I’m more interested with the TAC motor here…can’t see your misfires to be a separate issue….if so you chase your misfires first..finding it hard to believe you’re a novice knowing to check relay 44 !!

 

LOL! I hate to say it, but Google helped out a little. I only have one of those cheapy $79 code readers, so I can't do anything except scan/clear. The manager of the transmission shop where I had the rebuild said I could hook into their scanner and we can see where the misfires are occurring and possibly check tps voltage to and from. I'll post when I get it check out.

 

You will need to see if the TB motor is not binding and you can open the throttle blade manually…I would suggest if you want to get the best info and not from Google you can get a 1 month subscription to Alldata DIY for $19.99 and get the best Service Info and wiring diagrams…I’d invest with a good bidirectional scan tool that can scan all modules and you can get a good one for less than $500.00 now.

 

C5 Diag - I just swapped 44 relay with the Defog relay. Started right up with no mega misfire or any code relating to throttle body or tps. Stopped and started a few times and no code. Took the car for a brief run and I couldn't get it to do anything it's been doing. I did notice that some of the other relays were super-hot only after about 15 minutes - especially the fuel pump relay - and some also have brownish blemishes on the sides also. Kinda pressed for time tonight so Saturday I'll be able to highway it and really get on it. I'll let ya'll know what happens... Thanks again!!

 

Cool !!…so I guess you won’t be needing that new TB after all !!…and as far as testing the relay, resistance testing across the contacts is NOT the way to do it…dynamic loaded circuit voltage drop testing is and if you look at electrical testing in the Service Manual GM wants you to do this resistance testing…there are a couple things that may cause the relay to overheat…increased resistance across the load contacts and poor “terminal tension” of the relay blades…remove the relay and you should see “striations” across the blades denoting a good connection…if not the terminals are spread inside the fuse box and that will cause overheating of the terminals which will cause high resistance and lower current flow…I use a terminal tension test kit (pictured below) and make sure I have the same “pin drag” when removing and installing the correct size blade…maybe just replace the relay with new and I would go to a dealership and get an OEM relay…I replaced my fuel pump relay when I had my 2001 and it was about $20.00 at the dealer…not all relays are the same…some have a diode in them like the AC Clutch relay and some have a resistor…let us know if it’s a good fix and I couldn’t even imagine how many parts a dealer would have thrown at this with misfires and TB codes !!…I’m curious what my voltage drop is across relay 44…I’ll check it tomorrow.

 

Did a voltage drop test on my Ignition 1 Relay load contacts (30 and 87) and saw a 0.025 volt drop across the contacts…wondering what yours may have been ??