Choreo

Thanks Bill for the detailed response - looks like I still have some work to do!

Choreo

Since I am in somewhat of a time bind right now, I just ordered a new ignition switch from Gene to try. I will take my other one apart to see what is there and will just have a spare.

If the ignition switch contacts are bad, could that cause the testing machine at the local parts store to show "Low Regulator Output" when connected to the battery terminals?

Bill Curlee

All the microprocessor modules in the C5 operate on TWO 12 VDC inputs. One is "HOT at ALL" times and the other is "HOT in ON and Hot at START

If the ingition on voltage is low,,,YES it could effect the PCM which controls the alternator. If you want to know if the ignition switch is causing an issue, you can check the voltages at the fuses for all the
HOT in ACC and IGNITION ON" 12 VDC feeds to the modules.

When the problem presents its self,,, measure the voltages at the following fuses:

The one for the PCM is:

Under Hood Fuse Center, PCM Minni fuse# 16

BCM

Under Hood Fuse Center, BCM 13 Minni fuse# 22

If there LESS than battery voltage,,,,the ignition switch is the issue.

BC

Choreo

Great Bill! I will check this out tonight.

To add to the Drama, this afternoon I went back the the Parts Store and had them hook up their analyzer a 3rd time.

With engine running showed "Regulator Low Output" at the battery terminals (same message as before and after new alternator installed last Friday).

They were kind enough to let me try a new Optima in their parking lot and do a retest (I told them if it solved the problem I would buy it on the spot). With NEW battery installed they ran the test with engine running and it came back "Regulator GOOD"!

Thought we had found the gremlin, but then he suggested that I put my old battery back in and test it one more time just to make sure - this time with my old battery the test reported "Regulator GOOD" and 13.75 volts!

So, the confusion continues.

Choreo

Bill,

New ignition switch should be here is a couple days. In the meantime, I was trying to perform the tests you outline in this post above. I am not much of an electrician (yet) so I am not sure exactly how to perform this test (physically).

I see the two fuses in question and I have the multimeter set to VDC 20, but should I remove the fuses to preform this test or probe around them in place?

Do I just use the red probe at the fuse location and attach the black probe to a ground?

Should these locations be hot at all times even with the key removed?

Should I test with the key in the ACC position and then again in the ON position without the car running?

Sorry for my ignorance in this area!!!

Bill Curlee

No problem!

Turn the ignition ON. You dont need to have the engine on. Those fuses should only be HOT when the ignition is ON.

Yes,,,probe from the top of the fuse to chassis ground or battery ground. On top of the fuse there are two recessed metal ponts. You can read either one (if the fuse is good). You should read tthe EXACT same voltage that you have at the battery terminals. If it is much lower than one volt than battery voltage, that could indicate a voltage drop in the ignition ON circuit.

Choreo

OK... Today (after sitting all night)...

Battery POS to Chassis ground shows 12.11V (no ignition key inserted)
Battery POS to Chassis ground shows 11.96V (ignition key in ON position)
#16 Fuse 11.96V (ignition key in ON position)
#22 Fuse 12.0V (ignition key in ON position)

Bill Curlee

Those voltages look normal ( at this time). How do they look when the problem is happening? If you replace the ignition switch and that doesnt fix the issue, we will be able to further isolate the issue.

I wish you would have just cleaned your switch. You could have saved a few bucks but,,,I know what time constraints are!

Hope the switch fixes your issues.

BC

Choreo

I will definitely take the old switch apart and post photos if anything looks bad (then clean it up according to your instructions and keep it for a spare). Hopefully the new switch will be here by Friday?

It is hard to test when the problem is occurring (by myself) since it only shows up when the car is in gear (Drive or Reverse) and the brakes are applied. Usually, after I come to a stop, the vibration starts, if I let up on the brake and let the car roll a few inches and reapply the brake the vibration stops and the RPM goes back up from 400 to 500 RPM - regardless of the voltage readout. I am just guessing the two are related?

Also, the past few days, twice I also got the 1214 Code (EBCM) - then it went away on the next restart. So, something is definitely not right since I got the car back from the dealership last month, but can't point fingers.

BTW - What SHOULD the idle RPM be on a stock C5 in gear at a red light?

Bill Curlee

Were trying to prove your voltage bad and you keep saying you have an idling issue. Your car should be idling around 650 - 700 RPM. If you have a low Idle, your going to have a low alternator output voltage . Are you sure you don't have a cylinder misfire??

How does your car perform under hard acceleration?

BC

Choreo

Yes, the idling issue is what first starting me looking for solutions about a month ago. I had not noticed any "voltage" problems (at least as voltage problems since the car always started fine and ran fine except at red lights).

It was suggested by another Forum Member that the low idle may be caused by a bad battery - so I had that checked and he parts house said it was ok.

Another forum member suggested after that, that it may be the alternator, so I had that checked, it showed "Regulator Low Output" at another parts house and eventually replaced it a week ago today under warranty ($100 deductible).

Also, about a month ago right after I noticed the idling problem, I installed new Iridium plugs and High Performance (red) wires ordered from Gene. Idle was smoother afterward, but still dipped at red lights occasionally to 400 RMP (still does).

I never paid any attention to what the car idled at in Drive the past 8 years, I just know that the past few weeks it idles at 400 - 500 in Drive with the brake on and about 600-700 in neutral. When I accelerate hard or otherwise there are no issues. Just to try and be sure, when I took the car to the Dealership 1-1/2 weeks ago to verify a bad alternator, I had them check for cylinder misfire using their Tech 2. I stood there and watched the mechanic bring up that screen on the Tech 2 and it showed no reports of misfire at idle or reved up on any of the 8 cylinders - so I assume the plugs and wires I installed are OK.

Therefore, I am just "hoping" that the stumbling/vibration from the low idle when coming to a stop is related to the voltage as some forum members have suggested? Both the gauge and the DIC show the voltage dipping to sometimes 11.8V right now when first coming to a stop and then usually quickly increases up to 13.1V - 13.6V (today).

bestvettever

Hi, I'm a bit late getting into this thread, have you checked the tps, maybe your volts go down because the engine is not turning fast enough to charge properly, because of an idle problem related to the engine controls.--Below is an idle relearn exercise, of course the successful outcome of the exercise depends on the engine controls properly functioning.
SEE BELOW
Good Luck
++++++++++++++++++++++++++++++++++
Idle Learn Procedure
Idle Learn Procedure
Anytime the PCM or the battery is disconnected, the PCM looses power, or the PCM is reprogrammed, the PCM's learned idle position is lost. The engine idle is unstable when the learned idle position is lost.

Perform the following procedure in order to return the learned idle to the correct position:

Automatic Transmission
Turn OFF the ignition.
Restore the PCM battery feed.
Turn OFF the A/C controls.
Set the parking brake and block the drive wheels.
Start the engine.
Allow the engine coolant temperature to reach 80°C (176°F)
Shift the transmission selector into the drive range.
Allow the engine to idle for 5 minutes.
Turn ON the A/C controls.
Allow the engine to idle for 5 minutes.
Shift the transmission selector into the park range.
Allow the engine to idle for 5 minutes.
Turn OFF the A/C controls.
Allow the engine to idle for 5 minutes.
Turn OFF the engine for 30 seconds.


Manual Transmission
Turn OFF the ignition.
Restore the PCM battery feed.
Turn OFF the A/C controls.
Set the parking brake and block the drive wheels.
Transmission in neutral.
Start the engine.
Allow the engine coolant temperature to reach 80°C (176°F)
Turn ON the A/C controls.
Allow the engine to idle for 5 minutes.
Turn OFF the A/C controls.
Allow the engine to idle for 5 minutes.
Turn OFF the engine for 30 seconds.

Choreo

Interesting. So this procedure is supposed to be performed EVERY TIME the battery is disconnected? ...and the foot brake is never to be applied during the procedure?

I will try this after I install the new ignition switch (looks like it will be here next Tuesday) and see how that affects things first.

Not sure what the first two steps mean? Are they just saying, "With the ignition key off, reconnect the battery"?

Bill Curlee

I was just going to recommend the same procedure!

If the idle relearn procedure doesn't help,,,I recommend doing a cylinder balance test. Find someone with EFI Live and they can run the test for you. It will tell you if one or more cylinders is not pulling their fair share of the load at idle.

You can also run the test your self. Disconnect ONE spark plug wire at a time and see how much the RPM drops when that cylinder is not supporting the load. They should all be about the same. If you disconnect a wire and see little or no difference, that cylinder is suspect.

It could be caused by:

Bad compression
Bad Injector
Bad plug
Bad wire

Give the test a try and report the results.

BC

Choreo

Well, since you and Bill both recommended that I try this procedure, I went ahead and performed it tonight. After the procedure, I took the car for a 35 minute drive all over town and did about 40 full stops at red lights (both with and without the A/C on) and low an behold the idle never dipped below 500 RPM once and there was NO VIBRATION OR HESITATION at all. I tried both fast and slow stops - no problems at all. I am still hesitant to pronounce this problem solved until I get a chance to put it through the paces again tomorrow, but that was by far the best performance it has yielded since last December when the dealership had it apart for 17 days (never really idled well after that visit and I know they had the battery disconnected both in December and a few weeks ago in May).

I have never heard of this procedure before and I am pretty sure the dealership never performed it after reconnecting the battery (I know for sure they did not last May because I was there when they hooked it back up and drove it out of the shop - same with the alternator replacement last week - I was watching them the whole time).

So is it really necessary to do this procedure every time the battery is disconnected? Would changing out an air cleaner also affect this or is is strictly electrical?

Still not sure what RESTORE the PCM Battery Feed means - unless it means you are supposed to disconnect the battery first before performing the procedure? Just out of curiosity, how does the PCM know you are initiating this procedure?

The voltage was still moving between 12.1 and 13.0 tonight and the LED turn signals were also hyperflashing at nearly every intersection (I am guessing due to the voltage drift?). I have had these same Halo LED taillights for three years and they never hyperflashed once until the past few weeks. I have received the 3rd party harness that should cure the hyperflash symptom, but right now I am using the hyperflashing as a diagnostic tool as this is a new behavior. I am just taking a guess that if I can stabilize the voltage at low RPM the hyperflashing will stop (they do not hyperflash at constant RPM above 1000), but we will see.

Thanks for the great tip - I am keeping my fingers crossed - tonight was the first time in a long time I started to regain confidence coming to a stop (without keeping my other foot near the gas just in case).

bestvettever

Hi, glad to see the idle problem is clearing up. yes you are right in assuming that the phrase "RESTORE the PCM Battery Feed ", is engineer speak for make sure the battery is connected dufus. As if you could do anything without it connected. I'm not sure that you would have to do this procedure every time the battery is disconnected. Mostly the car will relearn during the course of normal driving and not show any bad attributes that most would notice while learning, by defaulting to default settings during the process. But in the case of mods, the circumstance, and configuration may be different enough to warrant a relearn procedure. As for the led signals, they shouldn't be so sensitive to normal voltage changes if they were engineered right for the car. They usually have a transformer that converts a small range of input current to a specific output. I suspect the circuit doesn't have enough of an input range built into it, but I'm not a turn signal expert. I'm sure bill may have some good insight into this.
Luck To ALL

Choreo

Ok, today I started experiencing just a slight stumble at a couple red lights right off the bat (dipped to about 450 RPM then back up), and the hyperflashing turn signals were driving me nuts. So I decided to go for broke (literally) and went to the parts store and bought a new Optima Red Top. Installed it and took the car for a one hour drive tonight. No idle problems at red lights and the hyperflashing completely went away.

So... I am guessing that even though the Battery tested good on the bench, it still was having some issues in the real world (I never get more than about 3 years out of a battery anyway without issues, so it was time to swap based on my history).

Therefore, unless things revert to something less in the next couple days, my guess is the idle and hyperflashing are cured.

This just leaves one "potential" issue to resolve and that is the voltage situation. I have seen posts on the forum that say what I am getting is perfectly normal and others that say I absolutely should not be getting this "drift" in voltage when coming to a stop. Other than the fact that I am monitoring the Voltage on both the gauge and the DIC, I am currently experiencing no adverse issues (yet), but if this drift is NOT NORMAL, then I need to correct it.

I now have...
• New Optima Red Top Battery (torqued to spec)
• New GM Alternator (torqued to spec)
• All the grounds I have checked so far look like new - absolutely no visual corrosion, tight connections and easy to remove the grounding nuts without issues (dry environment the past 8 years rarely driven in light rain). (torqued to spec)
• New Ignition Switch will be installed next Tuesday

Tonight the voltage meters (on the dash) showed 13.0 - 13.4 while driving and would drop to 12.1-12.6 at red lights.

Bill Curlee

Did you ever check the voltages at the alternator output terminal, and battery terminals to see if you have a voltage drop between the alt and battery??

The voltage on the IPC meter cam be deceiving. Read the voltage AT the battery and alternator and see if the IPC meter is accurate.

BC

071574

Had the same problems with my Tahoe and it was the throttle body needed to be cleaned. You might want to take the breather off and look inside the throttle body, if there is black buildup, you need to clean the throttle body with some cleaner. It will take two people to do this. One spreading and the other keeping the the car running. After I did this everything work like it is suppose to. I had everything check like you have and it ended up being dirty throttle body.

wildbadbill

you may try this-I had something similar 2 mos ago.
If you look at our factory wiring,from the battery the red wire goes to the under hood fuse box and than follows with another cable to your fuse box inside the car.So,the first cable from the battery to the engine fuse box carries the load of BOTH fuse boxes,and I happen to think it's to much,especially on hot days (higher resistance).
My solution was to remove the cable that feeds the in car fuses from the connection on the engine fuse box and put it on the battery direct-so from your battery you have two feeds seperate foe two fuse boxes.
It helped my readings on the DIC which measures the voltage on the inside fuse box....