Engine reduced power
Thread Starter
Racer
Joined: Sep 2014
Posts: 429
Likes: 28
From: Brooklyn, MI
Engine reduced power
1998 vert automatic, started car to take a little cruise, engine popped and CEL and traction control light on. Reduced power message displayed. Pulled the codes and got P1516 command verses throttle position and C1278 TCS temporary inhibited by PCM. Reset codes and lights still on engine idling high reduced power still on. Shut car off and checked code again still same Reset codes and this time stayed off and car ran as normal. Is the car telling me something? It is cold here in Reno this is the first time I have car out in this low of temp, this is the first winter. All comments appreciated.
Le Mans Master
Joined: Mar 2011
Posts: 6,835
Likes: 301
From: Columbia SC
Could be several things. Not uncommon to get "hicups" also that just "go away".
If issues come back post what codes you get and I will post the DTC diagnostics for you.
If you want the diagnostics for those codes now I can do that too, not at home now.
Mr. Sam
If issues come back post what codes you get and I will post the DTC diagnostics for you.
If you want the diagnostics for those codes now I can do that too, not at home now.
Mr. Sam
Melting Slicks
Joined: Mar 2012
Posts: 2,800
Likes: 456
From: USA
reduced engine power
Shortly after purchasing my 2001 I had a similar problem. DIC went crazy, reduced engine power message. I was not far from home so I limped home. I researched the forum and found a post that talked about the connectors in the doors. I pulled these apart and cleaned the connections and replaced and never had the problem since. Here is a link that mentions Bill Curlee's post here on the forum. This is what I did and my problem was solved. Hope this helps. 
http://ls1tech.com/forums/corvette-p...lp-please.html
I could not find Bill's post here thus the LS1 that used his post same info though.
http://ls1tech.com/forums/corvette-p...lp-please.html
I could not find Bill's post here thus the LS1 that used his post same info though.
Last edited by zachaeous; Nov 7, 2015 at 11:02 AM.
Drifting
Joined: Sep 2009
Posts: 1,862
Likes: 594
From: Prescott, Arizona
A symptom that clears after a shut down and restart could also be the ignition switch contacts burning and going bad.
If the grounds and door connections are not the problem, I would look at the ignition switch next.
If the grounds and door connections are not the problem, I would look at the ignition switch next.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,396
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
The 97 &98 C5s had known defective Throttle Actucation Control Modules. The one in my 98 Coupe went bad... Same symptoms.
Fitst things first. Remove the induction system.. Clean/replace the filter. Clean the MAF with MAF cleaner..
Examine the throtle blade and throttle body. The blade and opening will likely be very dirty inside.
Make SURE that the throttle blade can be opened and FLOPS shut when released. It WILL NOT snap shut!!!
It will ERRECT to the last known good idle position when the ignition is ON.
If you still have the issue after you accomplish the above, Inspect the wiring to the Throttle Position Sensor.
REP happens when the PCM detects that what you are telling the engine to do doesnt match to what the engine is doing.
The TAC module is mounted in the passengers fender on the outside of the PCM:
Open this pannel in the passengers fender well:
PCM/TAC TAC on the outside:
Fitst things first. Remove the induction system.. Clean/replace the filter. Clean the MAF with MAF cleaner..
Examine the throtle blade and throttle body. The blade and opening will likely be very dirty inside.
Make SURE that the throttle blade can be opened and FLOPS shut when released. It WILL NOT snap shut!!!
It will ERRECT to the last known good idle position when the ignition is ON.
If you still have the issue after you accomplish the above, Inspect the wiring to the Throttle Position Sensor.
REP happens when the PCM detects that what you are telling the engine to do doesnt match to what the engine is doing.
The TAC module is mounted in the passengers fender on the outside of the PCM:
Open this pannel in the passengers fender well:
PCM/TAC TAC on the outside:
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Thread Starter
Racer
Joined: Sep 2014
Posts: 429
Likes: 28
From: Brooklyn, MI
Thanks for the info will do tomorrow I guess while I have the induction system removed I will clean out the radiator. I also ordered a new ignition switch because I have had other intermittent electrical issues that will clear but come back in a month or so. If I am gaining access to the switch might as well replace it.
Racer
Joined: May 2014
Posts: 278
Likes: 0
From: Gering Nebraska
The wiring harness connection at the TAC module had moisture in it causing the same symptoms on my 2001. Problem would come and go. After drying the connection and a little dyelectric grease on the connector seal have no had other problems.
Le Mans Master
Joined: Mar 2011
Posts: 6,835
Likes: 301
From: Columbia SC
Bill Curlee is correct about issues with the early TAC modules. GM made modifications and if you need to replace it you can use any 99-04 one.
Here are the diagnostics for the two codes.
https://www.dropbox.com/s/l0l2ag8k6r...01516.pdf?dl=0
https://www.dropbox.com/s/bl9b7eyqdh...01278.pdf?dl=0
Mr. Sam
Here are the diagnostics for the two codes.
https://www.dropbox.com/s/l0l2ag8k6r...01516.pdf?dl=0
https://www.dropbox.com/s/bl9b7eyqdh...01278.pdf?dl=0
Mr. Sam
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,396
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
The issue was covered under a TSB and only addressed if the car had specific issues and DTCs. Mine died AFTER the warranty expired so, I had to deal with it. The module is a plug and play replacement.
Bill
BC
Bill
BC
Last edited by Bill Curlee; Nov 8, 2015 at 12:21 PM.
Thread Starter
Racer
Joined: Sep 2014
Posts: 429
Likes: 28
From: Brooklyn, MI
I worked on the problem yesterday, replaced air filter, cleaned throttle body, cleaned MAF checked connectors all good no corrosion. Test drove car for about 40 miles no further problems. Thanks for all the help.
Heel & Toe
Joined: Apr 2003
Posts: 20
Likes: 9
From: Lake Elsinore, CA
Reset needed?
1998 vert automatic, started car to take a little cruise, engine popped and CEL and traction control light on. Reduced power message displayed. Pulled the codes and got P1516 command verses throttle position and C1278 TCS temporary inhibited by PCM. Reset codes and lights still on engine idling high reduced power still on. Shut car off and checked code again still same Reset codes and this time stayed off and car ran as normal. Is the car telling me something? It is cold here in Reno this is the first time I have car out in this low of temp, this is the first winter. All comments appreciated.
I also had this happen when keyfob battery dyeing.