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LH Lead-Foot · 03-25-2018, 02:48 PM

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.

03-25-2018, 02:48 PM	#9
LH Lead-Foot Registered User Join Date: Jan 2018 Location: Omaha, NE. Posts: 214	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.