The DRL's go off too? Is there anything else you're not mentioning?

The DRL's going off and the codes would make sense together. Back probe the wires or even better hook up two small light bulbs to the wires so you can watch them work when it's both good and bad. The service manual says to connect a test light to troubleshoot this.

 

Hey, Mike, I'm afraid these 2 statements are contradictory

The 1st one says that the "front is all dark" when the problem is present and you engage the turn signals. In other words, in addition to the front turn signal that is supposed to be flashing (but remains OFF), you are saying that you are also losing the DRL from the other side.

The 2nd one says that the DRL from the other side remains ON as it should...

Which scenario is the one that's actually happening?
​​​​​

 

I'm sorry for miscommunication. Here's what happens:
When I use left signal, the left DRL goes out/dark, but right side DRL is on/OK. When signaling on right side, right DRL goes out/dark, but the left side is OK. Lionel, there are no other issues electrically, except my twilight Sentinel doesn't light the dash lights, but head and tail lights are illuminated. Hope this helps, and thank you all for your help.........

 

Try replacing the DRL relays, or just swap with other relays in the fuse box. If you swap, make sure they are the same pin count.

 

1) Burnt out bulb
2) Bad 4 way switch
3) Bad multifunction switch

Since you've checked both 1) and 2), Id start looking at 3).

 

Thank you for response, but new multifunction switch installed 2 days ago.

 

I'll give that a shot, Lionel. Thank you. Just to be clear, I ran the codes last night, and I must've cleared them recently-No more B2578, or B2583. Anyway, last evening I went out and tried the signals again, and each side still hyperflashed, but I left the left side signal on while I tried to connect the multimeter, and after 4 or 5 seconds the hyperflashing stopped, and it worked normally. So I tried the right side, and it hyperflashed for about the same amount of seconds, then it operated normally, too!!! Remember, car is cold, and before new multifunction switch was installed, they worked OK until car was driven 20 miles or so. How can I check the 2 wires GCG, you, and others suggested, if they're working OK? Just so you know, the car does have headers, and I would think underhood temps are higher than a car with factory exhaust. Perhaps I should get all new relays in underhood fuse box, because all are 20 year old originals. Thank you so much......

 

Oh, I didnt see that. Im at a loss then. Hyperflashing in a GM car is usually one of those three things.

 

OK guys, here is an update, of sorts. It has been raining every day here for several days. Next Tuesday, Sept. 15, or Wednesday the 16th, I'm taking the car on a 300 mile round trip. Whichever day has the best weather will be the day we take the trip. Since the on again/off again problem seems to be heat related, I'm sure the problem will show up on the trip at some point. I'm taking a multimeter AND test light with me, and I'll post up what I find, if anything. Thank you to all who have helped......

 

Looking forward to your updates. If the problem happens and you have a chance, take the opportunity to test the LT BLU and DK BLU wires as previously mentioned. Please, don't forget to do that

 

Thank you, I will report back. I'm almost certain the problem will manifest again. Lionel told me those 2 blue wires are at the C2 connector on the BCM. Do you happen to know which of the connectors on the BCM is C2? Thank you again.....

 

@grinder11 Hey, Mike! Quick question that might help us narrow this down: when the problem is happening, does the corresponding turn indicator light in the IPC blink?

This is very important because those indicator lights receive power from the corresponding front turn signal. If the indicators work, that means that the flasher signal (Pin D with PPL wire in MFS connector - see markings in schematic below) is successfully going through the MFS to Pin F (DK BLU wire for right turn signal) and Pin G (LT BLU wire for left turn signal) in MFS connector.

It also means that the flasher signal is successfully reaching Pin B8 from Connector C1 (LT BLU wire) and Pin A4 from Connector C2 (DK BLU wire) in I/P Fusebox (passenger's footwell), but it is failing to reach Pin C9 from Connector C1 (LT BLU/WHT wire) and Pin B5 from Connector C2 (DK BLU/WHT wire) in I/P Fusebox.

Please, let me know. Safe travels!

Gilbert


NOTE: If you want to look at the complete schematic, check Post 28 above.

 

Good morning GCG. To answer your question, the answer is YES. When the signals hyperflash, the IPC green arrow also hyperflashed. If a left turn, only the left rear and left IPC green arrow hyperflash, and the left front DRL/Turn signal go dark. Same scenario on right side, right rear and right IPC green arrow hyperflash, and right front is dark. In either case, the opposite side of the side that hyperflashes DRL is on. Signal left, right front DRL is on. Signal right, left front DRL is on. Thank you for response.......

 

That is pointing to you really needing to monitor the inputs right at the BCM.

 

Like I said your signal switch U know know that little lever on the left .......bench test part by its self ...and u may find ur issue ...

 

Keep up, it was already replaced without any change.

 

Where to begin.....OK, On Monday afternoon, before leaving for the "300 mile" trip (which turned into a 650 miler!), I went out to the garage, and pulled the passenger side lower fender well, to access the PCM and its 2 large female plugs. One red, one blue. I unscrewed both screws, and removed the 2 large plugs, AFTER disconnecting the battery, of course. I then sprayed contact cleaner into the female pins, then blew them dry with compressed air. Ditto for the male pins. Then I firmly pushed the 2 plugs back into the PCM. Then I tightened both plugs. Then I took my medium sized ball pein hammer, grabbed it by the steel end, and pushed up hard with the wooden handle, 1st one end, then the other, then tightened the bolt some more. Did both the red AND blue plugs this way. We left yesterday as planned, and put 650 miles on the car. All went well until around 260 miles. Then the right signal hypered out the rest of the trip. THE LEFT SIDE IS FIXED!!!!!!!!! No more left side hypering!!!!!! Since it was so late when we got home, I was too tired to check anything. I got up this morning, and right side is OK again!!!!! BUT-Since we were in very low traffic areas yesterday, I drove with the right signal hypering for miles at a time, hoping it will store a code. So even though right side is OK now, I must have an H code in there for that funky right signal. As I said earlier, the left side is FIXED!!!! I'll go out and report back ASAP as to what codes are stored. Thank you very much for all the help. I'm going to research which plug on BCM is C2, so I can check with DVM. Back soon......

 

OK, back as promised. I have NO CODES!!! Since the thing is working OK, I'm havIng a rough time getting it to malfunction when the time is right to check wires. At my age, it's hard (VERY!) for me to get down to the BCM in the footwell (thanks, GM!) and access those wires. Actually, I think it is only the dark blue wire now, as the left signal is good. Is there anywhere else to access this dark blue wire than at the BCM. If I can't, then I'm thinking the only way to try this is to bare the dark blue wire, then attach a reasonably long alligator nosed test wire that can be left in place for now. Then the next time this happens, I can carry the DVM with me, and attach the leads when it does act up again the next time. At this point, with an intermittent problem and no codes, I don't know what else to do. By the way Speedy 007, the first time you insulted me, and others on this forum, I gave you a pass, and even apologized. This time, not gonna happen. Your little smart *** crack about my lever "thingy" on the left side of my steering column was sarcastic, and uncalled for. This forum is to help each other, not insult one another. From here on out, please block me. Surely you are too important, and busy for someone like me. Thanks in advance.......

 

Thanks so much guys for your help on this. Believe it or not, and you'll like this, I think my wife fixed it!!! I'll make this as short as possible. To be blunt, she is ham handed, two bulls in a China cabinet. Recently we drove the car for over 500 miles. At around 550 miles, the right signal started hyperflashing again. The left has never given a problem after installing a new MFS. Anyway, I pulled over to get a pop out of the cooler in the trunk. I asked her to push in the 4 way flasher. She did, with a push that could have rocked the car if she was outside of it!! I even said "you don't have to punch it, just push it". Anyway, after I got back in, pushed the 4 way off, and away we went. Next time I tried the right signal, it worked!!! It has ever since. Never heard of this before!! So its either a 4 way going bad, or a bad connection on the switch itself. If it comes back, I'll update. Again, thank you.....

 

Bad connection would be my guess. The hazard switch should not make an individual front or rear light stop signaling. There are contacts that go bad often in the hazard switch so it has a bad reputation, but none of them connect between the MFS and the front turn signals. The wiring doesn't allow the hazard to affect a signal on a single corner.