FiberglassFan

Posting here in "Tech" EDIT: Ended thread that was also in "General"

I'm stranded again and towed home with "REDUCED POWER" displayed in the DIC.....Got it home and used my chart to clear all the codes....I DO have a broken wire to one of the speed sensors on the wheel hub, but have driving OK by just resetting the warning that tells me the ABS is faulted....I am getting an ABS code, which ought not to to disable the car, and now a PCM code that seems to disable the car. The engine starter will run, but no fuel pump will turn on, and seemingly no ignition. All fuses OK.....Big ussue seems to be the PCM code. No matter how I press resest, when in the code reset menu, it keeps bumping back. I press the reset, it goes out for about 2 seconds then comes back on displaying "PCM 1 code"

ARRRGGG!!! Is there a fuze I can pull, or remove the battery for a few minutes, to force a total system reset, or is it likely the PCM computer just blew up???

This is way beyond the PULL KEY-WAIT 10 SECONDS and I'm running out of money an patience. I jst cant imagine spending another grand or 2 on it right now...we just went through 2 grand in the past 3 months with pades & rotors, crank pulley, tensioners and belts, & etc....

dgrant3830

First off, send a PM to Bill Curlee. Secondly, the first thing he's going to ask is what the code is and all other codes. Post them here. Thirdly, yes you can pull the battery for a minute and it should reboot all the computers. I'll venture the guess that you loss communication between the BCM and PCM or you've got a bad ignition switch. Were there any other indications like wild things happening with the DIC?

FiberglassFan

Bill has come to the help of many of us!!! I'll try to get a PM off to him..gotta find his link to do so, but before I do, I'll go disconnect the main battery for a few minutes....Wish me luck..

When I insert the key from totally off, the DIC goes through the CORVETTE scroll, all the dash symbols come on momentarily as in a normal startup mode, and then the DIC display of REDUCED POWER comes up..and the ABS light comes on......turning the key to 'start' the engine results in cranking, ....turns over like normal but no start at all, noit even a burble....I do not hear the fuel pump coming on at all......and I have no way to know if the ignition is coming on or not. All fuses are OK, pulled all of them associated with IGN and fuel and the PCM and they are all good...

Went through the entire code retrieval and clearing process, several times, and get the ABS code that I was expecting, but am also getting a PCM code that I never saw before today, and that has come concurrent in time with the failure to run.

Over on the "General" slvrzo6 suggested the following ".....I had a similar problem about a month ago. My Car was stuck in Reduced Power Mode too. It ended up being the Ignition Switch, It wouldn't allow the system to get enough voltage and caused a bunch of weird codes to come up.. Thus Stuck in "reduced power mode".. Here is the Thread and FIX.. Bill Curlee maybe able to help you..

http://forums.corvetteforum.com/c5-t...yone-else.html

I'll be pulling the battery in a few minutes......
Jennifer

FiberglassFan

http://forums.corvetteforum.com/c5-t...yone-else.html

FiberglassFan

Pulled battery waited 1 minutes hooked back up ......now the DIC is all scrambled letters! No start.....

FiberglassFan

Pulled battery again....now the corvette by Chevrolet comes on as usual again, no scrambled letters...

Did a code retrieval
10-PCM 2 CODES
P0601 HC
P1518 HC
28-TCS 2 CODES
C 125 H
c 1276 HC

I can use the reset-codes feature to eliminate the codes except the P1518 HC, which will not delete...However, pulling the key and starting over will have all 4 codes re-appear. No other codes come up at all.

FiberglassFan

Found the following code info online...PM with all details sent to Bill Curlee...waiting to see what he says....

10-PCM 2 CODES
P0601 HC ( Internal control memory checksum error)
P1518 HC ( Throttle Actuator control module serial data error)
28-TCS 2 CODES
C 1255 H ( ECU malfunction)
c 1276 HC (Delivered Torque Circuit)

lucky131969

PM sent

Bill Dearborn

The P0601 is your problem. First, check voltages and grounds at the PCM. A computer doesn't always operate correctly if the voltage across it isn't high enough.

However, it looks like something has caused a problem in the program so when the computer runs the software it detects a bit error in one of the files. That is what is meant by a checksum error. One of the program files isn't as it was originally written. The diagnostic says to try and reprogram the PCM.

If the PCM cannot be reprogrammed you may need to replace the PCM. IE. your PCM has taken a SXXT.

Bill

FiberglassFan

Lucky and Bill...
Tomorrow I will pull the wheel and shroud and inspect the electronics and connectons/grounds....Fuse 17 is OK, so fault will be other end of circuit, or failed firmware/hardware in the computer.....

For almost a year I have been threating to one day rip out the whole stinking wiring system in the C5, install Kinsler injection with a mechanically linked throttle and and a top flight engine management system, Tilton dual master cylinder manually adjustable brake system, and then rewire the rest of the car with circuit breaker switches and high reliability manually controlled systems.....I'm really old school ...reliability and longevity wins over wiz bang techo crap that fails in 8 to 10 years....Fine for a disposable Lumina or some other crap car that will be in crusher about the time its paid for, but for Corvette, come on...we KEEP these cars on the road for decades upon decade... I have had the climate control apart 2 times to fix crummy solder joints with high reliability solder....No excuse for the junk solder they use, its just cheap and crumbles apart in only a few years....Grounding points! HA, what a joke, corrosion traps by design, And yet I LOVE my Vette, and the driving experience it delivers...I will suffer the slings and arrows it throws from time to time because when it is good, it is indeed SO good.

Thanks everyone for your help, ...Until the new day brings light and warm, and more diagnostics,
Jennifer in Oregon...

Bill Dearborn

Jennifer, you really wouldn't find that all those changes would make the car run any better. Really, there just aren't that many problems with the C5 electronics. They are very reliable. All cars have grounds and all grounds corrode. With the Corvette the grounds all go through wires and actually make it easier to locate ground problems. Try finding a ground problem on a metal car where the body is used for a ground path.

Bill

FiberglassFan

Yeah I know..but this is how I VENT!!! I really wouldn't want to drive a race car everyday on the roads....After the second time through, in which I got ALL the solder joints, on all the boards, the climate control has been fine..However, I do wish the traction control system could be permanently removed/disabled and the throttle set to instant response at all times... I get tired of turning off the TC every time I start the car.....A few years ago there was a product called Track Active that you wired into the TC button and RESET button to do the job for you..I ought to make up a little 555 timer circuit and a few relays and sush my griping....Bigger fish to fry right now, gotta make it run first!

slvrzo6

I really think it's your ignition switch! You have TWO of the same codes my car had when it had this problem, Plus your car is acting very similar to how mine was at the time of my ignition switch problem.. I'll be watching to see what happens.. GOOD LUCK.. .DO NOT TAKE THE CAR TO THE STEALERSHIP..

lucky131969

Bill,
Have you seen a P0601 error before? Since it is an internal error in PCM, is it ever a recoverable situation?

FiberglassFan

Double checked all the fuses associated with the PCM...especially fuse 17 engine bay fuse block, all OK....I't looking more and more like the PCM has fried. Fortunately, one of the 2 regional speed shops that specialize in Corvettes and Camaros is less than a mile away....Were getting ready to pull the car out of the gravel and hook it up to the Jeep for a tow up to the speed shop. He has all the diagnostic and programing equipment that can get me back on the road quickly..same fellow did my LSS-1 Edit install and dyno tune, so if the computer is fried, he can reinstall my enging and tranny map at the same time. If the computer is not fried, a re-program may do the trick...Crossed fingers... Once the computer issue is taken care of, I'll be taking the ignition switch apart and re-do all the contacts RE Bill Curlee thread on that subject, It is likely original switch, bought car with 64K miles and now almost 130K on the car, so I know its not a low hours/low time switch. Almost everything mechanical on the car seems to be fairly robust, but the electrical stuff seems to be pretty standard GM fare, good enough for about 8 years, and then fall apart....I have to rebuild or replace Climate control, radio, both column wands, wheel speed sensor connectors, seat control switch module on driver side, and more ****ling switch & sensor problems here and there...Mechanically, in all this time, the ONLY failure I have had was a crank pulley getting wobbly, just a few months ago. Of course, I have done the usual belts, twice, and tensioners - once, at 126 K miles, bigger springs and sway bars and a Ron Davis radiator, Stinger air cleaner and bridge, dyno tune, Z06 exhaust,brake pads a few times , and rotors...done at the time I bought the car with 65K and just recently at 126K, and I have trans and diff fluids replaced quite often too, but that is all general maintainence or performance enhancement, not outright failure repair. I have new rear wheel bearings ready to install, but even that is not critical, as they are just now getting a tiny bit noisy, and the fronts are still dead quiet! ...Mechanically the car has been quite robust, ...electrically, well I'm not a happy camper about that. I'll post again when I learn something new...
Jennifer

FiberglassFan

It is confirmed by the speed shop owner Steve that the engine PCM computer is indeed fried, just as we found from checking fuses, voltages, and cleaning grounds. It will not accept a re-flash program. Hopefully a new PCM will arrive tomorrow. The shop will install it and then "rebuild" my custom LS-1 Edit engine and trans maps for the newer code in currently delivered PCMs, and get it going. Might do more dyno time too and get my shift points at partial throttle settings raised even more that it was.
Steve also says there is some potential of something else wrong, but that it is not possible to go further in diagnostics until a functioning engine PCM is installed. We do know that we are getting codes from bad wheel speed sensor connectors....Funny thing was that I had reserved today to work on cleaning, adjusting and basically re-doing those connectors...Oh well, they will still be there for me to do after the engine runs again. I think I'll also rebuild the ignition switch as soon as I can too....It is getting old and they are a common trouble point WELL discussed on the Forum.
Jennifer

dgrant3830

I've never heard of a PCM outright failing like that before for no reason. Sure hope you don't put the new one in only to have it die as well. I understand that you really can't do much without a functioning one in there, but something caused it to quit on you. They normally just don't fail like that. I would be looking for whatever possible causes.

Bill Curlee

Save your old PCM.... I bet its still GOOD!!! My guess is that the IGNITION SWITCH is NOT providing the correct voltages to the PCM and it failing all the internal checks and test that it does. You can read the voltages on The PCM fuses.

Heres a copy of a post that I sent to someone to help them diagnosis their ignition switch for a NO RUN issue. The info can be used to check yours:

The key to this problem is having to hold it in the START position for it to run. There are THREE separate circuits that the car uses to power the cars modules.

They are:
HOT AT ALL TIMES
HOT IN ON AND START
Bulb Test

Finding this issue will be solved by turning the ignition switch to the ON position and checking all the fuses that are powered by the IGNITION SWITCH (HOT IN ON AND START) position.



If you let me know what year car were talking about I will come up with a list of fuses to check.

You will be using a Volt Meter, placing the NEGATIVE lead to ground and using the POSITIVE lead to probe the small metal test points on the tops of all the fuses that are powered by HOT IN ON AND START.

Once you find a fuse powered by HOT IN ON AND START missing 12 VDC when its suppose to be ON, turn the key to START and see if that fuse powers up during that switch position.

You still could have a bad ignition switch. Wouldn't be the first time a new part was bad.

If you still have the old one, use my ignition switch repair post to repair that old switch and see if that changes conditions.

The ignition key cylinder has nothing to do with the voltage out of the electrical portion of the switch,,,UNLESS,,,,it not allowing the actual switch to go to the ON position properly. See if moving the key slightly left or right of the ON position to see if that changes anything thing when you go to the ON position.

Ok,,,here are the fuses that your going to check:

Under Hood Fuse Center

ENG ING1 FUSE# 19

INJR 2 FUSE# 18

THROTCONT FUSE# 17

INJR 1 FUSE# 22

PCM FUSE# 16

F/PMP FUSE# 13

Instrument Panel Fuse block

BTSI BU Fuse# 21
BCM 13 Fuse# 22

Check the VOLTAGE on these fuses when the ignition is in the ON position. There should be battery voltage on these fuses.



Bill

FiberglassFan

It's the PCM....Once the whole thing was taken apart it was clear what happened....Long before I owned the car, it suffered a battery leakage. Acid followed gravity...The battery housing area looked nice and clean when I inspected the car before purchase about 4 years ago. I did not remove the inner fender to see inside. The area I COULD inspect looked fine, but it was apparently well cleaned up after some leakage, but not so down below where the PCM resides. There was a cheap Interstate battery installed, date coded about 2 months previous to my purchase. Upon driving home, I installed an Optima just to reduce the chances of future acid leakage, oblivious to the fact that leakage had already occurred, and corrosion issues started.

Fast forward to the failure of this week....When the wheel and inner fender was removed to inspect PCM wiring and grounds, a real acid mess was found. Corrosion was everywhere, all over the metal case of the PCM. All voltages and grounds leading to the PCM appeared to be fine, and grounds measured low impedance back to battery minus, indicating a GOOD ground was still intact. Connector plugs were cleaned up, and a re-flash of PCM attempted ....no response. New PCM arrived today with stock program....BINGO!! Fires right up!! Everything, EVERYTHING, works just fine.....Tomorrow its back on the dyno for performance tune. Steve, my tuner, said that he had seen lots of PCMs with acid corroded cases that worked just fine, but never had seen one that lasted so long after acid exposure, only to eventually have case failure and burn-out at such a later time...You could see where the case was compromised, and how with the passage of time and moisture exposure it finally corroded through and got 'crud' inside.

At least it runs again, as fine as any stock engine program will allow. and it will be home probably Thursday late afternoon, or at the latest Friday. Steve has has a lot other work this week besides mine, and depending on actual dyno time taken it might spill over into Friday....I told him not to rush, just take it easy and do it without time-stress.

I plan on rebuilding the IGN switch as a matter of course sometime soon....It is bound to fail at some point as it has the age and heavy use working against it. I still have to clean up all those pesky wheel speed sensor connectors too...Too bad GM could not use a metal in those connector that would not fatigue to the point of loose electrical contact pressure.

I was hoping to take apart the old PCM for inspection, just to see what failed from the presumed internal corrosion, but the new one came with an offer of a trade in credit, just like a core charge on refurb/re-man parts. Money wins that one! ...so we'll not see what was inside.

I DO want to give a heart felt thanks to everyone who has taken time to post and correspond with me. It allowed me to diagnose the failure mode to the point that I was pretty sure it was not a simple corroded ground or a power delivery problem. No, I did not enjoy the process of tearing into the car once again with multi-meters and probes, but I was sure willing to do it in hopes we might find the fault with something I could fix/repair at home...like the proverbial ignition switch. [ Bill, I printed out your entire tutorial with pix on rebuilding the ignition switch..Good work ..I'll be making use of that real soon !!]

At least the effort was not in vain...We gave it a good shot, I learned a lot, and arrived at the speed shop with a full print out of the codes and definitions, and the schematics/block diagrams of the suspect PCM area, Steve took a few minutes looking it over and said I had done all the homework and saved him some time. PCM was confirmed bad by Steve within minutes with a simple attempt to re-flash it....and double confirmed when the new unit fired up the car and all systems with no codes at all.

At the very least, I have learned a great deal more about my old C5. I am most grateful to everyone here who sent me technical guidance and advice.
It is indeed a cool group here, and a valuable part of the Corvette life.

So much still on the 'To Do' list....In addition to rebuilding the ignition switch, I need to install the new stainless over Teflon brake hoses I have, get the new rear wheel bearings in sometime in the next few months, and at some point remove/adjust the front bumper cover and right side fender to make everything line up right again after it got 'bumped' at the front of the fender a while back by a friend of ours who was NOT paying attention where the end of his car was. There is always something to do or repair....and over the past weekend I had a low beam go out in one of the H-4 bulbs in my T-84 headlamps...Thank goodness that one's a quickie!

Again, Gracious thanks,
Jennifer

FiberglassFan

[QUOTE=Bill Curlee;1567910246.......................
Heres a copy of a post that I sent to someone to help them diagnosis their ignition switch for a NO RUN issue. ..................[/QUOTE]
See Bill's the full post above....

A concise and to the point test procedure! ....I had already checked most of the voltage points you mentioned and found B+ where it needed to be, enough to determine that we had good power to the PCM and Throttle Control boxes.and in addition,t hat I had good grounding on each system as well, I am printing out your post here because it has everything one needs to know for thorough tests of this system...It will go into my growing binder of REAL Shop & Technical information learned here on CF, that is not included in the official GM manual. Thank goodness for people like you and many others here on CF. I would be lost without the Forum and the good people who help each other out here.
THANKS for your generous gift of time and expertise! MANY of us here really appreciate it.

Jennifer