Throttle problem
 

I’m doing a 2003 5.3 in a 55 and am loosing throttle response. If I rev it up sometimes it will die and the engine light comes on with code 1518 (TAC Module). After it’s restarted there is no pedal response. It idles fine. Also if I clear the code and hold the pedal down suddenly it will rev up then just go back to idle even with the pedal to the floor. If I slowly accelerete it will rev a lot higher. Kinda stumped.

Re: Throttle problem
 

I would try to unplug the battery cable and make sure all the connections are good . unhooking the battery is better than just clearing the codes.

Re: Throttle problem
 

Did that and it goes away temporarily. Also took the grounds off and cleaned the surface on the block where they bolt to.

Re: Throttle problem
 

Sounds like a mismatched part problem to me. Did the TAC, pedal, TB and tune match?

Re: Throttle problem
 

Like ls1nova71 mentioned, it could be mismatched components (or a defective component). Also, double check that the TAC module is getting power at the same time as the PCM. If one is powered up before the other (or one doesn't get power in the ignition "crank" position) you'll get the P01518 code.

Re: Throttle problem
 

I dont think the pedal and TAC Module is from the same donor vehicle. How do I remedy this now?

Re: Throttle problem
 

To remedy it, you will first have to figure out exactly what it is you have. Pics would help, but for starters, tell us what PCM you have, blue/green or blue/red? Also, what does the throttle body look like? One plug, or two? Is the TAC all plastic or plastic with an aluminum base? The TAC and PCM will both have part numbers on them to narrow it down further, so let us know what you have there.

Re: Throttle problem
 

It is a blue/ red pcm, one plug on the tb and aluminum base on the tac. Hope this helps. My computer is being a pos for uploading pics.

Re: Throttle problem
 

The code P1518 is a loss of serial data on one or both of the UART data lines. The diagnostics aids point out several other issue to set this code. #1 Low battery voltage at TAC module. #2 Short to B+ on the TAC's ground (Cruise Sw. / Brake Sw. / Fuses / Etc.)
#3 TAC module is powered up with key off, short to B+ on ignition feed. #4 Bad connections with UART, power and ground. Wires to check by terminal are; TAC C1/7 (PNK) hot in run & start. Terminal 15 (BLK) ground. C1/6 (LT BLU) brake B+. TAC terminals 12 (ORN/BLK) UART to PCM to C1/14 & TAC UART to PCM 13 (DK BLU/WHT) to C1/15.
If the TAC module is mounted under the hood, check for green tint on terminals, clean with electrical terminal cleaner, use dielectric grease on all. Check ground termination eyelet for loose or painted bolt area, clean as need and use a "Star" washer to ensure solid ground. The OEM configuration uses a 15A fuse from the buss, powered by the ignition switch hot during cranking and run both. If your B+ is present only on RUN, The TAC module will out of power sequence with the PCM as posted earlier. You can use two 1 watt diodes (1 crank / 1 run) soldered together this ignition switch led to power a relay's coil with permanent ground, and switch B+ for this power mode with a 15A fuse for circuit protection.
FYI, the donor vehicle uses a BCM and it requires 5 different ignition sw. inputs for correct power modes. The PCM uses 4 power modes; Hot at all times B+(C1-20-57) / Run-Start-ACC (C1-75) / Run-Start (C1-19) / Start B+ (C2-59)
It's very easy...Ha, Ha. Retired ASE Master with GM eSI stand-a-lone CD up to 2004.

Re: Throttle problem
 

Blue/red PCM needs the all plastic TAC and has the throttle body with 2 connectors. This is your problem. You need a blue/green PCM.

Re: Throttle problem
 

Had the guy that built the harness look at it and he thinks it’s a mismatched tac and pedal. Motor is a 2001 and the the pedal itself is all plastic so he thinks it’s out of a newer unit.

Re: Throttle problem
 

I'm with ls1nova71 (and your harness builder) in that you have mismatched parts. As long as you end up with a matched set of PCM/harness/TB/TAC/pedal you can get a working setup.

I'm speaking under the assumption that you would like to keep your PCM/harness as you've already spent time/money on those and a different (blue/green) PCM won't just "plug in". With that in mind, if you have an all plastic pedal, it's at least a 2006 model pedal and NOT compatible with the early DBW. If your TB only has a single 8 pin connection, then it's 2003 to early '07 and also not compatible with the early DBW. The correct TB for your ECM has two connectors (one for TPS and one for the throttle blade motor). If your TAC has the aluminum bracket (as opposed to all plastic), it is also not compatible with the early DBW setup.

Here's a link with some pics of the different components.

http://chevythunder.com/drive_by_wire.htm

Re: Throttle problem
 

This pretty much sums it up. So basically what it appears you have is a 99-02 PCM, 03-05 or 06-07 TAC and a 2006 pedal. That is a really messed up set up. You need to pst up what part number is on your TAC, its printed on it with a barcode. That way we will know if your pedal will work. If it will, you should only need a new PCM.

Re: Throttle problem
 

I may have found an earlier pedal to use. Hopefully that’ll fix it. The motor comes up as a 2001 and I didn’t change the throttle body on it. Attachment 1768417

Re: Throttle problem
 

Throttle body has a single 8 pin from what I can tell

Re: Throttle problem
 

That TB is the "late" Gen 3 style used from '03 to mid year '07. The TAC module you have is part 12590008 and was only used from '06 to mid '07. You said your pedal was all plastic, so it's probably the '06 to mid '07 one as well (as opposed to the mid '07 and up Gen 4 pedal)

So, you've got an 01 harness and PCM but all the DBW parts for an '06/early '07.

Unfortunately, just swapping the pedal isn't going to get you going.

Re: Throttle problem
 

Throttle body has a single 8 pin from what I can tell

Re: Throttle problem
 

From what I can tel this is what I have:
Engine: 2003- return style fuel rail and single 8 pin plug on the throttle body.
Pcm: 2001-02 red/blue plug and part number 12200411
Tac: 2006-07- plasti tac with metal mount and part number 12590008

Yeesh what A mixmatch of parts. Can I get away with just changing the tac and pedal or is the throttle body going to be an issue?
The harness is already built to accept the red/blue pcm and single plug throttle body.
Also he showed me on his laptop when it was connected to the truck it said 2001, would that have been the year of the motor or computer?

Re: Throttle problem
 

Like dayj1 said, changing the pedal isn't going to help. The fact that you have a blue/red PCM, means its an older '99-02, and there's no way it will work with the newer parts you have. You NEED a newer PCM with a '06 tune......

Re: Throttle problem
 

The 411 PCM was only used until '02, so when it showed 2001, that's the year of the PCM/tune in it. It WONT run the newer TB. If your harness is set up for the 8 pin TB plug, you should be able to switch the red plastic parts on the PCM connectors with green ones, get a '06 PCM and be in business.

Re: Throttle problem
 

Ok that’s not as bad as I thought. Wasn’t sure how different the two pcm’s would connect. So this tac and pedal that I have should still work?

Re: Throttle problem
 

Im not at home so I cant check the TAC part number, but if dayj1 says its a 2006-7, then I would believe him. So, you have a matched TAC, throttle body and pedal, su unless the wiring harness is not wired correctly then you should be alright with a PCM swap. The harness has to have been either repinned for the 8 pin TB or its really a blue/green with the plastic parts of the PCM connectors changed, because GM never made a blue/red harness with that TB.

Re: Throttle problem
 

The harness was built from scratch. I’ll talk to the guy that built it today.

Re: Throttle problem
 

Hmmm, I'm not one to put people down, but I'd be leary of the skills of someone who would make a blue/red harness with a throttle body connector like that.

Re: Throttle problem
 

That’s kinda what I’m thinking too. He insists that an older tac and pedal that matches the pcm will remedy the problem. Guess I’ll try it his way before I say told you so.