Recieved the Infamous "REDUCED ENGINE POWER" message :/
 

It threw a few codes

most recent-
P1514 Throttlebody performance
C1278 TCS Temporarily Inhibited by PCM


DTC P1515 Control Module Throttle Actuator Position Performance
DTC P1516 Throttle Actuator Control (TAC) Module Throttle Actuator Position Performance

This has been doing this on/off for a while. It was actually fine for a few months. So I didnt bother messing with it.


It stalled on me a few times when driving at low speeds, also it feels like it surges/bogs a little on its own when idling/driving. that usually happens a few mins before it sets the codes and then the REP light comes on

Could this be a TAC module going bad? From what I've read, this reduced engine power crap seems to be a common problem.

Any ideas on what I should do?

I figured this weekend I'll-

Check ground wires- front ones had a lil corrosion. I cleaned those up.
Check connection at TAC module
check to see if throttle blade is sticking- Checked and it's not sticking

Any other ideas? All help is appreciated :cheers:

Last night it threw a P1120 code as soon as i started it and went into REP mode

today it threw a P1515 and a P1293

just did some more searching and came across an interesting thread. THis should be helpful http://forums.corvetteforum.com/c5-t...tion-long.html

It may be because the year, but there's a table in your ECM, that governs the density of year entering the motor. Its more like a threshold amount, and can happen with intake + exhaust boltons at the least. I've gotten it a few times before I found the table I needed to change. Ever since I did that, these codes have never come up again.

What are your mods? Any chance you've got a tune and or data log?

Very interesting info. I didnt know about that

mods- 2001 vette, auto, Fast 90mm intake and tb, vararam, 25% UD pulley, longtubes, off road x pipe, staight pipes for an axleback, 3400 converter, 3.42 gears.

UPDATE- I cleaned up those ground connectors up front in the lil plastic cases. also switched out my TPS for one that I had from another TB. So far so good :D But then again, it was ok for a few weeks when i didnt do anything to it lol. Only time will tell

I have hp tuners, but my laptop is broken. looking to get a replacement very soon

I think the table is in the Eng Diag section of HP Tuners. For me, the code only showed up when I went WOT.

Hi---don't panic easy fix---Its a common isssue on modded LS's
NOTHING is wrong with your throtttle body or communucation or your Tracttion Control or ABS
The P1514 is the root cause of all of the codes and "reduecd power mode "
When modding-- you eng's airflow will become greater than the "predicted airflow " in your tune --All you have to to is to go to the
"Predited Airflow table" (in EFILIVE table C6101") and ADD about
30-40% to the ENTIRE table--It does require use or either HP or EFILIVE to make these changes- Once changed it won't go into red. power mode--- In the mean time -all you have to do is start your car and turn it off 3 times and the red. power will be turned off and reset
Simply turning off the DTC permanently or deleting the codes won't do it either---
The reduced power mode uses the ABS and TC systems to redsuce the power--hence all the ABS and TC codes--They should disappear after the correction-----

Another Question about Reduced Engine Power
 

I'm sure this is a dumb question; but, I Ned to ask anyway before I spend a lot of time and money troubleshooting my problem.

The car was wrecked (not by me). The air bags deployed and have not been reset. There is a wire to the drivers side front brakes missing ( I assume this is the ABS lead)...

Will this cause the Reduced Engine Power message? I cannot reset no matter what I try. Cleaned all the engine area grounds, etc.

Please help.

Thanks

I forgot to check back here lol. I have HP tuners. I'll definately look into that. big thanks!

98tadriver; I had the same issues as you listed. I did a lot of research and ended up replacing my ignition and the car has been great since. The brass pins that make contact with the metal tabs inside begin to arc and wear down due to the high current that runs through the ignitiion. Once I popped open the old part sure enough 3 of the pins were bad which would reduce a clear flow and throw out codes of all kind and cripple the performance of the car overall.

no kidding? Luckily all has been well with my car. just out of curiosity,what part of he ignition did you replace?

I have hp mpvi pro. Where do I adjust predictive airflow table
 

I'm new to boost. Car is a monster but goes into reduce engine power anytime I get on it really hard.

I'll chime in here since you have HP Tuners. Go under the "Engine Diagnostics" tab, then under "Airflow" you'll see "Throttle Position Sensor" and you'll see under that "calc-airmass-P1514/P0068 Error" table. Open the table and Highlight entire table and multiply by 2. Re-flash to car and that's it.:thumbs:

Will this still work if I dont have a mass air sensor. Car is currently speed density tuned. Ty so much for your help.

Hmmm. That's a good question. Here's an explanation of the table and how it works.

[ECM] 14040 - Calculated Airmass vs. TPS vs. RPM - P1514 Error: The VCM uses this table to determine the maximum airmass (g/cyl) the Electronic Throttle should be passing at a certain TPS position and RPM. If the measured airflow exceeds this value then P1514/P0068 is set.

I would say if you're getting the P1514 code this should correct for it. I can't hurt. It's only a look up table (hall monitor) for the PCM. You're kind of hijacking OP's thred though so try it out and let us know if it helped.

Need help
 

😪

I don't know what to do any more. I'm getting a P1221 and P1220 code that does not clear. Even with the engine off and the ignition set to on, I clear it using an obd2 plug in computer as well as the c5s onboard dash computer and I get no luck at all. The code comes right back as soon as I clear it. I have tried turning off the car and turning it back on several times, disconnected the battery, cleaned the battery terminals, cleaned the battery ground, checked and cleaned the throttle body, made sure no water was in the intake or MAF, replaced the TPS sensor next to the throttle body, and finally cleaned the two grounds at the front of the engine bay.

Even with all of that done, the codes keep coming right back and the engine stays in reduced power mode. I have only had the car for a month and a half. 98 C5 automatic coupe with 97k miles. Has a Corsa cat back it has had for years. Installed a Vararam air duct and drop in high flow air filter and Replaced spark plugs and wires a month ago.

​​​​​​Probably the most important part that has me baffled. I was installing a catch can yesterday in line with the PCV when I realized the plastic PCv cover was broken in half. I replaced the PCv and plugged in all of the hoses correctly. The reduced engine power mode started right after I turned it on and the engine started vibrating HEAVILY. I have triple checked the hoses around the catch can and even tried turning it on with the PCv disconnected and I still get the same code. I already threw $100 at it with the new TPS replacement and a few hours with all the aforementioned troubleshooting but I am at a loss. Any help is greatly appreciated :(


Broken PCV
https://cimg7.ibsrv.net/gimg/www.cor...f2fb2b0205.jpg

If you have a boosted C5 and are still running your MAF, you've probably exceeded the limits in HZ of the MAF causing the computer to reset.

Turns out I accidentally cut the wires leading up to the TPS while cutting foam around the plastic tube that leads to the PCV while I was replacing it. Fixed the torn wire last night and all codes went into history mode and I was able to clear the CEL. Reduced engine power mode has gone away as well.

https://cimg3.ibsrv.net/gimg/www.cor...b8243a97be.jpg
https://cimg7.ibsrv.net/gimg/www.cor...692e7b35d1.jpg
https://cimg9.ibsrv.net/gimg/www.cor...458d05a850.jpg
https://cimg6.ibsrv.net/gimg/www.cor...82f907a759.jpg