Daytime Running Lights are not working

Check fuses/relays, several items can be on one ground so if something else electrical doesnt work, then it may cause your running lights not to work. else not to work too. Did you check the alternator ? here is a guide

https://www.2carpros.com/articles/how-to-check-a-car-alternator

First lets clear up a common misconception. You want to have the diagnostic fault codes read but "the dash lights dont come on". Fault codes are stored in the Engine Computer even if the Check Engine light goes off. The light does not have to be on for the codes to be read. In fact, there are well over a thousand potential fault codes that can be set, and only about half of them relate to something that could have an adverse affect on emissions. Those are the only codes that have to turn the light on. There can be codes in memory that you never know about if the light doesn't come on.

The Check Engine light is the only light that relates to fault codes. All of the other symptoms you mentioned suggest a charging system problem. Since GM redesigned their generators for the '87 model year they have had a huge problem with repeat failures. They develop voltage spikes that can destroy the internal diodes and voltage regulator. When one of the six diodes fails you will only be able to get exactly one third of its design current rating, and that is not enough to meet the demands of the electrical system under all conditions. When the battery has to make up the difference the voltage will drop as it becomes discharged. Your car has a lot of computers on it and they are very intolerant of low voltage. They'll do weird things including shutting down and turning on warning lights.

Most of the time with a bad diode the charging voltage will be close to normal so that can't be used as a test. You need to have the generator professionally load-tested on the car. If "ripple" is very high and the most current it will develop is around 30 amps for the common 90 amp unit, have the generator replaced.

It is common to go through four to six generators in the life of the car. To prevent those repeat failures replace the battery at the same time unless it is less than about two years old. As they age they lose their ability to dampen and absorb those voltage spikes.

A slipping belt will do the same thing as the bad diode I mentioned, only in a different way. Three things are needed to generate a current mechanically, (in a generator). They are a magnet, (electromagnet, in this case), a coil of wire, and most importantly, movement between the two of them. That's where the belt comes in and it is why all generators are less efficient at lower speeds. If the belt slips there won't be enough movement so the generator will be unable to produce its full current.

With a bad diode, two thirds of the output circuits are dead and that will also reduce output current.

A parts store can usually read any fault codes for you but they can't do the charging system load-test. Some of them have test benches to test generators if you bring them in but those only show if it's working to some extent, not to its full capacity. A generator under full load takes over five horsepower to run. The puny electric motors in test benches are less than one horsepower. To be able to run a generator under full load the pulleys are geared down a lot and that reduces the generators speed so again, it can't produce its full output. To be accurate, testing has to be done on the car, and the procedure always includes raising engine speed to 2000 rpm.

You might try checking at a Sears Auto Center. In the '80s they did the full battery, charging, and starter tests for five bucks.

Depending on which engine you have there are different ways the belt is tensioned. Unlike the older V-belts, the flat serpentine belts rarely slip due to excessive wear. Most commonly they slip due to a weak or rusted spring-loaded tensioner pulley. If you tug on the belt and see the pulley move, then spring back and hold the belt tight, the squeal would be caused by a misaligned pulley. Again, unlike the V-belts, these flat ones are absolutely not forgiving in the least with a pulley that is tipped or turned. When a pulley is tipped it makes the belt slide across it as it goes around it. 1/16" is more than enough to set up a horrendous squeal.

If the belt feels loose or the tensioner pulley doesn't take up the slack properly, that can cause the squeal and low generator output. Get that taken care of before the charging system is tested.

Are you having a problem with drl lamps? Some of the relays in the fuse box may be the same, check them out, if the same, swap relays, just for testing, see if problem goes away. If nothing changes, the problem isn't the relay.

No BCM it has its on microprocessor see below EWD how the DRL is wired in the electrical system.

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