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Please help me, I’ve done everything I can and followed every post I could but I can’t shake this issue. Cars been down for months with a pcm p1518 code, tps is replaced, app (accelerator pedal) is replaced and the tcm (throttle control module? Behind the passanger fender cover not pcm) replaced and no progress, this issue was intermitant and now keeps the car in limp mode. HP tuners sees no throttle position, I have checked all the grounds and wires with a multimeter and no issues. I don’t want to buy a new harness but feel like it’s my only hope, maybe cleaning the grounds again.
please let me know any ideas or if it’s possible that the code is stuck and how to reset it.
also tcs code C1278
near Albany NY and may be interested in sending to a shop. I have potentially admitted defeat. ):
Last edited by 1997 issues; Sep 19, 2025 at 07:36 PM.
Trouble codes are not part numbers !!…follow the flow chart below and if this testing is over your head seek out an auto electric shop in your area…we can’t diagnose this for you especially since you’ve been trying to fix this for months…BTW, every time you replace a part you do a “repair verification”…each of those parts you changed needs to be tested…never assume they are good especially if you bought them from Amazon or EBay.
Sounds good this is great to have, I’ll give it a go and keep track of my results, just to check, these is no situation where the code is stuck and the tcs code is likely a result of the p code?
also is this information available for free online or is there somewhere I should go?
I also don’t have a physical manual for this car which may be needed if it keeps persisting.
again thank you and updates soon
Okay, I went though everything:
1. Yes
2. Yes
3. No
4. REP
5. 8.9v 8.9v
11. 0v
12. Yes
13. Yes 1.6v battery is dying but still in range
14. Way to high like .7 k ohms and other was 1.1 m ohms, Yes OL
15. PCM fully removed. Tested the tac 16pin plug serial wires #12,13 both OL
17. Yes measures at .0-.5 ohms
18. 1.5 volts on Both 12 and 13 (brown and orange and black)
I have 2 TCM’s and they don’t change anything, pcm connectors have lots of white dust corrosion so I’ll see about contact cleaner and dielectric grease for them. I’ll charge battery and see in the morning. Idk what I’ll do if the pcm is dead, seems like for a 97 it’s around 2k for one. The other years are a lot cheaper but idk if they plug and play. Also will find an obd2 scanner and see if it can’t find any accelerator pedal position, (hp tuners could not).
and ideas are super helpful, even if it’s clean the grounds again, I have not got to the ones that are behind the block or under the headers.
If you do “data driven diagnostics” you would have solved this instead of just guessing…I enclosed the “flow chart” for that DTC…did you use it ??…most of these flow charts are based on using a Tech 2 or factory aftermarket scan tool.
Yeah idk if you can see it, maybe not but I went though every test and get step 27 bad tac module “Replace Tac Module”… ): did I kill one and buy a bad one? Thus my questioning if it’s possible to test outside of car.
at one point in time the car would not get out of limp mode and I unplugged and re plugged in the tac module and it drove fine for 10 or so.
Well where did you buy the module ??…the only thing you can check if you have power and grounds going to the module…whenever testing with key on make sure battery is always above 12.45 volts.
Any other tests with the app sensor or the ignition? Some people have talked about these? Just would want to do everything before a new tac is on the way.
I still have a p1518 reduced engine power code. And no pedal position, I’ve tested continuity between the app and the tcm and the tcm ign power supply. All check out with a dmm, I find mysef with an issue I have a very good dmm and I get .60k ohms for the tac ground to chassis, I have a 1.30k ohms for battery ground. I ran a spliced ground for the tac to the chassis with an alligator clip and a cheap autozone wire splice thing ( it reads 0 ohms). Same p1518. Should I replace the ground strap to battery? Seems to be cheapish? This is the battery ground to the passenger side of the engine block. Honestly any ideas? I’ve tested everything I have 2 tacs 2 app sensors and all wires between them and the pcm are fine.
might take apart fuse block or just start running a ton of grounds. Idk I’m lost now.
Resistance checking is useless…the only thing I check for resistance if it is called out in Service Information like a fuel injector resistance check or a CAN bus circuit for a C6-C8…sorry but can’t help you with those readings…loaded circuit voltage drop testing is how it’s PROPERLY done !!…I’ve had electrical training with the best automotive electrical instructors in the country and they stress this type of testing.
Okay I did a load test on the tac and fuse 17, anything else to do it on?
all checks out, and voltage test on grounds aswell
does the app ground somewhere else?
No throttle, p1518
