So recently my c5 started saying reduced engine power after I ran it out of gas and now wont go over like 15 mph. I limped in a mile to an auto zone and cleared the codes thinking it was because I ran it out of gas. after clearing the codes it ran great for a day or two. How ever when I went back out to start it up again yesterday it is saying the same thing. as soon as I get off work I am going to check the pcm codes with the message center and I will post them on here. ANY help is much appreciated!

 

I had the problem last month, it took me 3 weeks to track down the problem which was wires broken on the Throttle position sensor but no damage showing on he insulation and without someone here telling me to hold the plus tight and take each wire as far back as I could get and pull on it hard but not hard enough to pull it out of the plug. When I did 2 of them just stretched where the rest were snug. I pulled the two that stretched till they broke the insulation. I soldered them back together and added heat-shrink and it fired up and ran great. In my checking I did find some other things like bad vacuum lines and other wires that had the insulation rubbed off.
Get the codes, if they indicate a sensor check the wiring.

I went ahead and ordered new pigtails for the TPS, MAF, and CPS because they all were showing the wear of over 300,000 miles.

 

alright got the codes....
10-pcm
p1120 H C
p1220 H C
p1516 H C
28-tcs
c1236 H
c1278 H
58-sdm
B0016 H C
B0026 H C
B0051 H C
U1096 H
A0-LDCM
B2282 H
B2284 H
U1064 H
U1096 H

A1-RDCM
B2283 H
B2285 H
U1064 H
U1096 H
B0-RFA
C2120 H
It must be worse then I thought... lol

 

I am not an expert but I would bet the farm your reduced engine problem is the throttle position sensor or TAC module

I think I would check all the wiring going to the throttle body



Someone more knowledgeable than me will surely be able to help you out with more detailed troubleshooting.

P1120 TP Sensor 1 Circuit
P1220 TP Sensor 2 Circuit
P1516 Command vs Actual Throttle Position Performance (TAC Module)

here are a couple threads to look at
http://forums.corvetteforum.com/c5-s...odule-bad.html

This one said he replaced the tac and throttle body and it fixed it
http://forums.corvetteforum.com/c5-t...1515-help.html

This one seems to be a bad throttle body
https://www.corvetteforum.com/c5-tec...and-codes.html

Check the wires on the throttle body, all the grounds and check the wires under the battery for corrosion


Throttle body and tac are both very easy to replace, I had mine both off tracking down my problems
The tac is attached to the PCM with 3 screws and has 2 wiring harness plugs. You access it by through the front passenger side wheel well panel remove the wheel and I think about 6 screws.

all the other codes other than the SDM codes are history and not current codes.
Try clearing them and see if they come back


The SDM are codes I have not saw before and are not in my list

From google they appear to have something to do with airbag deployment. Has the car been in a crash? Have you ran a carfax report or does it have a salvage title

B0016 Right Front/Passenger Frontal Deployment Loop Circuit
B0026 is driver airbag
I would definitely check up on that.


EDIT
went through thr pages I had saved when I was having problems and found another one related to your problem
here is a link telling how to check the sensor
http://www.gearchatter.com/viewpost14227.php

 

cool man ill give those a read I appreciate the help. I will also be sure to check all the wires and grounds under the battery and going to the TB. The car has been in a wreck and has a salvage title I have pictures of the damage and of it being fixed.

 

I would be willing to bet that you have no airbags.

Check the wires good, mine did not have any visible damage but when the bad ones were tugged I could feel it stretch where the good ones were firm. I assumes that over time the slight flexing at a certain point finally caused them to break.
Might be a good idea to remove the TB and clean it real good with some carb cleaner.

 

First off, the codes ending in H indicate History codes, so I would disregard those. The ones ending with C indicate current problems. I had the same three TPS codes on my 98 Coupe (P1120, P1220 and P1516). And I found the problem by going around all the sensors in the engine bay and wiggling wires. I grabbed the wires on the Throttle Actuator pigtail and wiggled them also. Sure enough, the car kicked itself into Reduced Engine Power. I ended up ordering a new pigtail and soldering it in. Fixed all my problems.

**EDIT** Simple fix, But spent months (and lots of $$$$) trying to figure it out. New TPS, TB, TAC Module, MAF, two weeks of professional help, no luck.

 

H codes do mean something. They happens for a reason. Could have been a weak battery, reconnecting the battery, a power issue in or to that module. So, they are used as a troubleshooting clue.



musclecarsrock68

WHY,,,,,,,,,,,,,,,,, , Are you going to AUTOZONE to read the DTC. You can do it from the drivers seat. The procedure for reading your own codes with the BUILT IN CODE READER is at the bottom of theis post:



Jeffwilson34

CLEAR all your DTCs and see if any of the history DTCs come back.

Post those and we can go from there.


musclecarsrock68,,, Here ya go:


READING YOUR C5 Engine Diagnostic Trouble Codes (DTC)

This procedure should be carried out any time you experience a problem with your C5. Most inexpensive store bought aftermarket code readers will ONLY read power train DTC’s. Reading the DTC’s with the C5 built in code reader will allow you to read ALL the modules in the vehicle.

The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold the OPTIONS button
4) While holding OPTIONS, press FUEL button four times within a 10 -second period.

Initially, the on-board diagnostics go into an Automatic Mode which will cycle through each module and shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each module. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.

There are two types of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes. More likely it's an indication of an intermittent malfunction.

Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.

Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles. There are a few body module DTC’s that if set will prevent the module from operating properly. Once the DTC is cleared, the module will return to full function. This is not true for power train DTCs.

If you have never read and cleared your codes, there will probably be a lot of old history DTCs. It is recommended that you clear your codes and see if any come back during a driving cycle. Those are the ones that you need to concentrate on diagnosing.

Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.

NOTE and a WARNING. You can read the DTCs while the engine is running. I pull mine up all the time while driving.
WARNING. Don’t become distracted while reading DTCs while your driving and cause an accident!!!!! Use common sense and drive safe.

These are some very good C5 Diagnostic Trouble Code (DTC) explanation web sites!!! They also explain how to read the DTCs

Here are some very good sites that explain what DTC mean:

http://www.gearchatter.com/viewtopic11755.php

http://www.obd-codes.com/trouble_cod...d-ii-codes.php

Make sure to include the H or C suffix when you post your DTCs!!

NOTE!!! Start the car and let it idle. Then take it for a drive and cause the problem to occur. When you return home pull the codes BEFORE you shut off the engine.


Do NOT discount the codes with the H following them. They can provide an audit trail for issues going on with the car. They ARE important in diagnosing problems.

Post ALL the codes that you pull with the engine running..........

Some codes go away WITHOUT setting an H code when you shut the engine off. I suspect you will have several codes that will show C or HC that do NOT show when the engine is turned off.

 

I only took it to autozone the first time because at that point I didnt know that i could read and clear codes in the car, after reading around some I found a post explaining how to do it, Witch is how i got the list that I posted earlyer, However I did not know how to use the Manuel mode or how to clear them so thanks for the info. I went out and cleared the codes, but there was one category I could not clear, I would hold the reset button the same I did for every other code category but it would still show that it had 3 codes if I remember right. so I took it for a quick test drive and it is still running great. with it parked and idleing I started wiggling the set of wires going into the TB witch didnt make and difference. Im not sure how many plugs go to the TB but I only found one. I guess it would be helpful info for you guys to let you know it has a fast 92 on it with an ls2 TB the guy i got it from said he had to buy some wire adapters to make the ls2 TB and fast intake work right with the car.

After messing with those wires with the car still running I checked for codes and it says no codes for all of them except for one category that I could not clear. So when I get the chance later I will take it for a longer test drive and see what happens.

 

What module will not clear the DTCs and what are the DTCs?

Yes, the 90 MM TB had one plug BUT,, the OEM harness has TWO plugs that connect to that harness. On plug for the OEM Throttle Position Sensor one plug for the OEM Throttle Stepper Motor.

Make sure that the TWO plugs that plug into the adaptor harness are not corroded and properly connected. One batch of the CASPER adapter plugs had a small hole in the rubber plug that allower water to get into the plug.

BC

 

It is SDM
B0016 HC
B0026 HC
B0051 HC

I unplugged the two plugs that went into the same wire loom as the plug for the TB and they both looked clean inside. I also started the car and messed with both of those two plugs again to see if it made a diffrence and it did not not. I took pic of each of the two plugs and am trying to put them on here so you can see if i am checking the right plugs

 

plug with pink green and blue wires going into it

plug with yellow and brown wires going into it on opposite side of TB

 

those are the airbag codes, I still think you have no airbags or if you do they are not hooked up correctly.

Hope you get it going, I know how aggravating it can be when trying to track down electrical problems.
I have researched things for hours then grab a flashlight and go out in the middle of the night and try it.

I was out working one morning around 3AM and a cop drove by and thought he caught someone stealing a car. Not run to hear someone say do not move then look up and see a gun pointed at you.

 

LOL!! That story made my night! I can relate. I was on a business trip up in Portsmouth NH. I couldn't sleep one night and at 2 AM I decided to go out in my car and do some tweaking on my PCM Tune with EFI live.

I made some timing changes with EFI Live and I was sitting on the side of a country road reviewing my data log info and a State Trooper knocked on the drivers window and said " What are we doing to night? "

I bet he thought I was watching some PORNO on my computer!!

So, I said... " Believe it or not, TUNING MY CAR. "

He said,, "Well,,thats a first for me.. "

I explained the whole thing and he laughed and said have a SAFE NIGHT.

If he would have been around 10 minutes earlier, I would have probably been in JAIL. Did a first/second gear WOT run.

I was adjusting the timing to get rid of some KR in some of the timing cells.

Bill

 

I went out to start the vette up this morning and the rpms jumped right to 2k at idle, and the message center started saying reduced egine power and then service traction system so I checked for codes with it still running and this is what I got.
10 pcm
p1120hc
p1220hc
p1516hc
28 tcs
c1278 c
58 sdm
b0016 hc
b0026 hc
b0051

 

Bill is the man with the answers I am sure he will have some better ideas than me.

Had you done anything after shutting it off last time?
the PCM codes all are Throttle control codes that really look like some short in your wiring harness somewhere.

The TCS code is saying the PCM temporally turned off traction control, I would be willing to bet that is because of the PCM codes and if they are fixed it will go away.
Most electrical components either work or do not. It is odd for one to randomly start and stop but loose or bad wires do.

before I found my broke wires, I had decided to find the problem by making a new wiring harness for Throttle position sensor because that was the one that was causing me to pull my hair out.

I had printed off the pinout for the PCM plugs, bought a new pigtail and already had enough wire I was only waiting on the small pins that would replace the ones going to the PCM. At that point I had the PCM and TAC temporally sitting in the battery area, I had removed the battery surround plastic and Fuse box holder.

Here is a question for Bill, When I was doing all that I found several large color coded connectors some round and some flat that looked like a split for the whole harness so that it could be replaced in sections if needed.

After I had fixed my problem I realized it may have been possible to use a continuity tester and test each wire from the pigtail to the large connector, rather than removing the PCM and testing them on the PCM plugs. Is this correct?

If so could he possibly check the continuity at those connectors and possibly find the bad wires or could one connectors be damaged or loose? He said the car had been totaled in an accident and had a salvage title so it is possible that something in the wiring was damaged in the crash and not fully repaired.

 

No I didnt do anything after shutting it off last time. I have spent a decent bit of time now checking wires and am really having no luck.

 

Just spent over a year to find my trouble was crimped splices on the wire harness going to my TPS. Removed all crimps and soldered the wires and car has run perfect for a week now. Good luck.

 

I have found that these cars are very sensitive when sensor wires are concerned.
A good crimp which works fine on almost anything else will cause problems with these for some reason.
The only connectors I have found that work are the ones used to connect the wires for electric firing of professional fireworks.
You stick the wire into the holes with all the insulation on them and them use a tool that pushes splicers into the wires. They also have some type liquid inside that makes them waterproof. They are rated for high temps. The only problem is they only work on smaller gauge wires. I have also noticed if a wire runs close to the coil or plug wires the EM field that leaks can cause the PCM to get incorrect readings

My rear O2 sensors are turned off but when I had the capped off harness temporally next to the plug wire the PCM threw a rear O2 trouble code. I moved the wire and the code went away. It is not a faulty plug wire, they are new quality wires. You can take an em meter and put it close to any plug wire and watch it flip out.

If you could rig up and hide it inside a wall some type of old coil and plug to fire from a switch or random timer. Have some ghost hunters come in with their EM meters you could really have fun with them. They freak out if their meter picks up a small field. A coil and plug will peg out their meters because they have them set for very sensitive EM fluctuations

 

I was driving the car the other day on the highway and the reduced power problem happen again. im not sure if it died before i got pulled over or if it died immediately when the problem started. I was more worryed about getting over 3 lanes with out hitting anyone.
Normally i could reset the codes and start it back up but this time it would not restart. I turn the key over and it just clicks. I dont think it is because of a bad battery, everything else works and the flashers stayed on for 2 hours wile waiting on a tow truck. then I put my fully charged jump pac on it and it does the exact same thing. just one click. Hopfully I will get a chance to get under it ay hit the starter tomorrow wile someone turns the key to see if that helps. Wile bored I pulled the codes that were stored just to see if there is a difference.
10 pcm
p1120h
p1220h
p1221h
p1516h
28 tcs
c1255 h
58 sdm
b0016 hc
b0026 hc
b0051 hc

Do the differences in the codes tell anything about why it might not be starting? and I have a stock ls1 intake i plan on swapping in place of the fast to see if it clears up the other problems when I get it to start. I have an intake and throttle body off of a 5.3L sitting around also, any idea if the 5.3L TB will work with the ls1 intake on the car?