Hey guys, hopefully somebody can help solve my problem. 2000 FRC, originally (several weeks ago) the starter would click when I tried to crank it but would then crank on the next try. This only happened a couple of times before I put it on the tender then all was good .One night recently I made a couple of stops on the way home and leaving my last stop I started the car and it was running similar to reduced power (no cel or any warning lights) also had a mild backfire when I would try to accelerate. Got it home and tested voltage at the battery and alternator 12.6 battery 14.2 alternator, however after being on the battery tender a little while it ran great. This has happened a few times now and each time charging the battery helps. I have since replaced the battery but now keep it on the tender. In the mornings all is perfect, leaving work in the evenings if I have to make a stop I still have the same above issues until it is back on the tender. Even though the alternator is showing 14+ on the volt meter could this be a charging issue? I pulled codes from the DIC today after this happened but these codes could be from when I replaced the battery, not sure if they're from that or this issue. Codes were:

B0502, B0507, B2482, B2282, B2284, B2283, B2285

Any info is greatly appreciated!

 

Welcome to the Forum and Merry Christmas !!...how is your electrical knowledge ??...if you have a voltmeter let me know and we will see if we can help you out...might be an ignition switch problem but without having the car act up it may be a little tough to diagnose !!...none of those “body” DTC’s you have shouldn’t be problem !!

 

Thank you and Merry Christmas to you too!
I do have a voltmeter handy. Part of this issue that has me baffled is every morning after being on the tender all night it runs flawlessly. Every afternoon I usually experience the problem, even after new battery. Is this common with a bad ignition switch?

 

I had experienced a bad switch myself last year but I diagnosed it pretty quick...a no start until I looked at the cars voltmeter with key on and I saw I had 8 volts...I cycled the key a bunch of times and it started...I knew my battery was good and fully charged..you can select the voltmeter on the DIC and see what it reads with key on...it your battery is fully charged you shouldn’t be seeing that...best to read your alternator charging voltage across the battery terminals !!...also when I turned the key on I did not hear the fuel pump prime...you may not be getting enough current flow through the switch and the fuel injectors and coils aren’t getting full “juice” and then no power like you’re experiencing !!..oh, and don’t go by the voltmeter as your charging voltage !!

 

I've got 12.1v on the DIC with key on engine off. Alternator output is about .5 a volt lower checking at battery while running versus checking at back of alternator.

 

0.5 DVC is a reasonable voltage drop.

Check & or or replace the TDR relay, Thief Deterrent relay...

Michael.

 

The best way to check alternator is doing a “voltage drop” check on both positive and negative side of charging circuit engine running...with black lead of volt meter on alternator B+ and red lead on battery positive with engine running with some loads on I like to see .2 to .3 voltage drop...check the same way but black lead on alternator case and red lead on battery negative...I like to see .1 to .2

 

Thanks for the help, I will check all of this when I can. Getting ready for Santa Claus so not much more time at the moment .I did however check for a draw... Voltmeter in line between neg cable and battery neg post, .20A (200ma?) after car was asleep.

 

Measuring 14.2V at the alternator and 12.6V at the battery strongly points to a wiring issue. Use the voltmeter and check from the case of the alternator to the battery negative terminal and from the output terminal of the alternator to the positive battery terminal. The measurement with the high reading points to the wiring with an issue. If the negative measurement is high then check the main negative wiring. If the positive measurement is high then check the main positive wiring.

My bet would be that the wiring connection at the big post of the solenoid is dirty and needs cleaning. Take it apart and sand the terminals clean and then put it back together.

 

Ok, I went ahead and pulled the ignition switch and found a couple of burnt contacts. I cleaned it up per write up I've seen in the forum. When finished I started it up and checked voltage. With it running I had 14.89 at back of alternator and 14.7 while running at battery. Took it for a ride and after about 20 minutes I started have the running rough issue .I tested voltage during that and had 14.16 at back of alternator and 13.93 at battery.

 

You have about a 0.23 volt voltage drop on the positive side whether the car is running rough or not...0.23 volts is OK !!...what is the number on the ground side just for grins ??...any DTC's ???...erase those body codes and see what you have the next time the car is running but check before you shut the car off...would be helpful to have a scan tool to look at some data PIDS so we can find some direction to go for you !!...it's hard to diagnose just based on symptoms !!

 

Ok. I'll check that too. I also checked back of alternator for AC voltage, depending on where I ground I get .19 to .5
Any AC voltage is a bad diode, correct?
But that wouldn't cause driveability issues would it?

 

.5 volts AC is WAY too much (50 Mv max (.05 volts) and YES YES YES it can cause driveability issues especially with any AC sensors which themselves produce AC...knock sensors (possibly your feeling of reduced power issue)..ie...retarded timing and rough idle….wheel speed sensors causing ABS issues. Also modules may reset if not getting good clean voltage. One of my buddies here on the Forum was having issues with his wife's Tahoe...ABS and knock sensor DTC's...first thing that came to mind was too much AC ripple..he had over 1 volt AC if I can remember...and his alternator was hot as you know what...new alternator fixed it !!...BTW, you'll have some AC ripple...just put your DVOM on AC and read it at the battery too !!

 

Replaced alternator and there are no more signs of AC current and no more signs of a draw. Went for a fairly long ride and thought all was ok, stopped for gas and immediately upon restarting it was running just like reduced power again. No warning lights and no codes when it does this.

 

So you're saying when you started the car without even your foot on the gas it seemed like there was a loss of power...any throttle response ??...without any DTC's and not having a scan tool is going to make this pretty hard to diagnose without firing the parts canon. Maybe you can pick up a scan tool...I use one called the Blue Driver that operates off my cell phone and I always keep it plugged into my DD...it's like $100.00 !!...Let's just try some things without having to spend any money...how about trying this:
1) check your air filter
2) clean your MAF sensor...you can disconnect the MAF sensor harness and see if the car runs better at idle and under acceleration...it will throw a DTC but that's because of it being unplugged.
3) this doesn't cost a lot of money but I'd change your fuel filter
4) Since you know your way around a DVOM run the car at idle and now connect your DVOM red lead to battery positive...find your PCM fuse #16 underhood and connect the black DVOM lead to either of the 2 metal test points on top of the fuse...the voltage drop across the ignition switch should be around .2 volts or so...check that !!

Like I said without looking at some data PIDS you'll only be guessing !!...you said you had a back fire when you tried to accelerate so you're running lean if it was from the intake !!...good luck !!...BTW where are you located ????

 

Ok. I'll check all of that. Its strange, the car will run perfect initially. Then usually after being shut off and restarted it will feel and run like a plug wire is off. That's the best way I can describe it. Only twice has it started it while driving, its usually upon a restart . when it "backfires" its the exhaust, if trying to accelerate.

 

A exhaust back fire can sometime be from a rich mixture and the air-fuel is igniting in the exhaust system...if you have an O2 sensor stuck lean the PCM will start adding unnecessary fuel which will give you that rich air-fuel mixture but normally it will throw a DTC...I'm kinda leaning toward your MAF sensor "over reporting" airflow at idle and those rich fuel trims...the PCM is thinking more air is entering the MAF sensor than actually is so it will start adding fuel...cleaning the MAF is what you would do to fix that !!

 

Very odd indeed.

Open the Thread in C5 Tech, the very first Sticky Thread. Long Read...

Poor Grounding will cause all sorts of odd issues in any late model car, the large number of electronic modules. There are several Threads regarding the Ground locations and how to service this problem. Loose or Corroded grounds can be intermittent, just like your problem. Grounds might not be your issues, but it is a good place to start. You will be surprised what you read in these the posts..

Me, I'd go ahead an service the Grounds in the Engine Bay, starting with the Battery to Frame ground connection. And the Connections at your Battery if you haven't already. This will eliminate these from your list.

Reduced power may be a hint. There are electronic models that will cause this directly. I don't recall which models will cause a reduced power mode, a search may provide a list that might assist.

Me, I'd read for Codes all the electronic modules for codes via your instrument Panel. If there No codes, that would be very puzzling... You might try turning off the Traction Control and see what happens.

good luck,

Michael

 

Capt. Mike, the 2 sensors that can illuminate the "Reduced Engine Power" are the APP and MAF sensor...the OP feels like the car is in REP mode but no warning indicated...just a loss of power I believe !!

 

C5 Diag,

Yep, I just re-read post #1.. I got Side Tracked...

I have an ongoing prob with my tire pressure sensors after anew set of tires. So I was stuck on reduced speed, daa. Thanks for the head-up

One of this dealer employees broke one sensor and days latter two more failed. I been dealing with Reduced Speed and 7 trips back.. Their call Thursday said they had yet another new sensor. I expect it's China parts and not Delco as they say... Oh, and two new front tires because the balance weight was too large,, Continental. My HHR Panel (FWD) would immediately complete a Major Power Reduction with a front wheel that started to Spin, was a PITA.

APP and MAF sensor.. Well We all try to believe that all Visually Displayed and audio alerts mean that the a error with be logged in the appropriate module, somewhere. Nope, I've seen enough myself to dispute that thought / statement. At least the owners car has the later ECM and not the early ECM.

I'm not clear for me if he has checked all the modules on his Instrument panel, so hopefully he does so there's at least that data could help..

However, "14.89 at back of alternator and 14.7 at the battery"" is generally too high for an AGM even a liquid wet cell, Battery. There's no technical info that I've personally read as to the max VDC without electronics damage in any GM ECM or other modules. From personal experience, in many MPU (micro-processor ) designs, over voltage is Fatal, and this circuity involved creates a significant mount of heat esp in power hungry modules like a ECM driving 8 coils and 8 injectors.

But, I'm still wondering about poor grounds in this C5. And if so, a module(s) or Sensor, all electronic contain electronic components) could have been damaged, but not Dead Yet. . Electronic Semiconductors don't do well with poor grounds. I typically go overboard of circuit trouble shooting and start review a similar design in my head.

At any rate, he got some tests and reading ahead. Hope he solves this problem soon.

Thanks,,

​​​​​​​Michael..