dbw help 2002 LQ9 DTC P1518 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ragtp66 · 03-15-2022, 02:01 AM

I have a complete swap from a 2002 Escalade EXT I owned and drove the truck for over two years prior to the swap. I took the Engine, 411 PCM, TAC module, APP (gas pedal) and the harness from TAC module to the APP. Followed Brendan's harness cleanup from LT1swap dot com. With my TAC module connected it takes the PCM down I get no communication with scan tool and the fuel pump relay signal wire has constant but pulsing voltage on it. I have checked all my pinouts are correct clean and not backed out. I have checked continuity as well as voltage drop not seeing more than 100mv drop on any circuit. 5volt refs check out good. I have tried disconnected TAC motor connector, tps, APP pedal which should only leave power, ground and serial data lines and it still instantly takes the pcm down. if I disconnect the TAC module 16 wire connector the pcm communicates as it should and the fuel pump relay comes on for 2 seconds for priming and then off as it should. I have tried swapping TAC modules I have 2 others from an 01 truck as well as the two APP -gas pedals no change.
My tuner uses HPT and turned off vats, removed egr, evap, ac, and automatic trans as I am using a t56.
Grounds are all clean to bare metal clean and tight. I have additional ground straps from block to frame and from firewall to block.
All new american auto wiring harness and dakota digitals if that matters.
I do not have any of the cruise control wires or the CHMSL supply voltage on the 16 pin TAC connector hooked up. I did not think I needed this since I am not running an automatic I thought I could wire it later when I add cruise control. APP and TPS sensors sweep as they should in opposite directions using an analog meter. The throttle body blade has the same pulsing as the fuel pump control wire if touch a finger to it while observing the test light on the FP relay I can feel in my fingers what I am seeing on the test light.

Any help would be greatly appreciated.

ls1nova71 · 03-15-2022, 08:58 AM

I would almost guarantee this is a wiring issue,, but without seeing it,, it can be hard to find.What did you use for a harness between the TAC and the pedal? You have to cut them out of an 02, as they aren't separate like the 03-07. Are you sure its wired right?

ragtp66 · 03-15-2022, 03:01 PM

I removed the tac wiring from the main harness from my donor. Double check pin assignments at both Tac module and APP and 16 pin connector to TPS and TAC motor on throttle body
https://imgur.com/a/8FqkKnF

03-15-2022, 02:01 AM	#1
ragtp66 Registered User Join Date: Jan 2019 Location: Joliet,IL Posts: 5	dbw help 2002 LQ9 DTC P1518 I have a complete swap from a 2002 Escalade EXT I owned and drove the truck for over two years prior to the swap. I took the Engine, 411 PCM, TAC module, APP (gas pedal) and the harness from TAC module to the APP. Followed Brendan's harness cleanup from LT1swap dot com. With my TAC module connected it takes the PCM down I get no communication with scan tool and the fuel pump relay signal wire has constant but pulsing voltage on it. I have checked all my pinouts are correct clean and not backed out. I have checked continuity as well as voltage drop not seeing more than 100mv drop on any circuit. 5volt refs check out good. I have tried disconnected TAC motor connector, tps, APP pedal which should only leave power, ground and serial data lines and it still instantly takes the pcm down. if I disconnect the TAC module 16 wire connector the pcm communicates as it should and the fuel pump relay comes on for 2 seconds for priming and then off as it should. I have tried swapping TAC modules I have 2 others from an 01 truck as well as the two APP -gas pedals no change. My tuner uses HPT and turned off vats, removed egr, evap, ac, and automatic trans as I am using a t56. Grounds are all clean to bare metal clean and tight. I have additional ground straps from block to frame and from firewall to block. All new american auto wiring harness and dakota digitals if that matters. I do not have any of the cruise control wires or the CHMSL supply voltage on the 16 pin TAC connector hooked up. I did not think I needed this since I am not running an automatic I thought I could wire it later when I add cruise control. APP and TPS sensors sweep as they should in opposite directions using an analog meter. The throttle body blade has the same pulsing as the fuel pump control wire if touch a finger to it while observing the test light on the FP relay I can feel in my fingers what I am seeing on the test light. Any help would be greatly appreciated.

03-15-2022, 08:58 AM	#2
ls1nova71 Registered User Join Date: Dec 2009 Location: Independence Mo Posts: 4,119	Re: dbw help 2002 LQ9 DTC P1518 I would almost guarantee this is a wiring issue,, but without seeing it,, it can be hard to find.What did you use for a harness between the TAC and the pedal? You have to cut them out of an 02, as they aren't separate like the 03-07. Are you sure its wired right? __________________ My '72 short bed build. http://www.ls1tech.com/forums/conver...6-0-4l80e.html 5.3 swap into my RUSTY '71 C10 http://ls1tech.com/forums/conversion...71-c-10-a.html Last edited by ls1nova71; 03-15-2022 at 09:18 AM.

03-15-2022, 03:01 PM	#3
ragtp66 Registered User Join Date: Jan 2019 Location: Joliet,IL Posts: 5	Re: dbw help 2002 LQ9 DTC P1518 I removed the tac wiring from the main harness from my donor. Double check pin assignments at both Tac module and APP and 16 pin connector to TPS and TAC motor on throttle body https://imgur.com/a/8FqkKnF

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