Bought a 1991 Coupe (AT, L98) back in late March and have been enjoying it a great deal so far. Having a few recent issues I need help with that I will try to describe in as much detail as possible. I am very new to doing my own work on and diagnosing issues with cars, so bear with me on my descriptions of these problems.

Car was trouble free until I went out of town for about 12 days in late April, early May. Got back to a dead battery. Charged it up overnight and was able to start it no problem. Drove it to an event about a 30 min highway drive away and went about my business for about 6 hours. When I returned, it had trouble starting but still managed after some determined cranking. Figured it maybe needed a little more time on the charger, so I connected it again when I got home with a plan to have the battery checked out the next day.

Next day I drove it to a shop (required a few attempt to start again) and they said it needed to be replaced. I guess the deep discharge killed it? Bought a new battery and replaced it myself. I am now assuming I have a parasitic drain and am leaving it on a charger at night. That's problem 1, but I will deal with that later once I have more time to diagnose.

Problem 2 is that since I replaced the battery, the SES light has come on (and later gone off). I pulled codes H32 and H22. I seem to be conflicting or confusing information Googling around regarding what those mean (again, I am new to this), so I thought I'd bring it here for a more direct answer. Not sure how concerned I should be since they don't seem to be active codes, and I do wonder if voltage issues from the previous battery had anything to do with them.

Problem 3 is (maybe) the most concerning, which is that since the battery was replaced, the car has also started making a pretty loud humming sound in the rear of the vehicle. It's difficult for me to pinpoint exactly where it is, but I will say it's easier to hear inside than out. It starts as soon as I start the engine and persists throughout the drive at all speeds and when I park it again. Could be fuel pump, I guess? Nothing about the drive seems to influence the sound very much. Possibly braking changes the timbre a bit. Best I can describe the sound is somewhat like a lawnmower operating in the distance (enough so that that's what I thought it was at first lol). Very strange. For what it's worth, this does not seem to have an operational impact on the vehicle (so far), but I am worried it may eventually.

I am concerned that whatever this sound is may be related to the codes from earlier. I'm wondering if forcing the engine to start on a bad battery may have caused the above problems? I feel stupid for doing it, but nothing I can do about that now.

Any help would be appreciated. Sorry for the wordy post, but I figure more information is always better than less.

 

1: If the battery went dead in 12 days, it was at the end of its life. The full discharge finished it off.

2: Code 22 is Throttle Position Sensor voltage low. I doubt there is anything wrong other than possibly an intermittent connection on the gray or blue wire at the TPS itself. For now, I would clear the code and see if it comes back. It probably won't. (Don't replace the TPS. It is almost certainly ok.)
> Code 32 is EGR test failed. This is a fussy code. This code sets at highway speed after a period of time. The SES may go out on the same drive. Check all the vacuum lines including the block on the EGR solenoid itself (ask @Natty about this). Check the EGR valve for ability for the diaphragm to hold vacuum. With the engine running lift the diaphragm in the EGR valve, The engine should stall or run really poorly. << This tests for restricted passages in the intake manifold or plenum. If this all checks out, clear the code and see if it comes back.

3: The sound is not related to the Codes.
It could be the fuel pump. Odd that it got noisy with a battery change. Turn the key to RUN, but do not start. The fuel pump runs for 2 seconds and stops. Compare the "hum" to the noise you hear with the engine running. I'm not sure what to suggest, as I said, a battery change shouldn't affect the fuel pump, but that is probably what the hum is. I'd ignore it for now.

 

I can add that you should look closely at fuel pump as suggested above. The pump in my 95 had a noise when i bought it. wasn't horrible and car ran fine. Over time the whining started getting worse which made me worried that it was starting to self destruct. Take the advise to turn key and listen to the pump noise as it primes. That is a no cost diagnostic step. I put new new pump in and noise gone.

 

Oh, regarding the battery, I should have mentioned that it was manufactured Sept. 2024. Was installed by the dealer prior to sale. IMO should not be dead yet, but that's what the diagnostics say. Dealer would not play ball on replacing it. Not thrilled about that, but it is what it is.

Very much appreciate the info on those codes! They have not returned, and the light has not come back on, so I'm hopeful it won't. But I'll look at those things for due diligence.

And yes, I checked the fuel pump priming sound and it is indeed much louder than before. I agree that I wouldn't think the battery swap itself would have caused the issue, but I am also now realizing I was wrong with what I stated above. I first noticed the noise when I was coming home from getting the old battery tested, with the old battery still in the car. I decided to ignore the noise then until I got the battery replaced, thinking it might be related. Is it possible that the hard starts or any other part of driving on an old battery could've put stress on the pump? That's my concern. Apologies for misstating the issue above, I should have checked what I wrote!

If it's not related to any of the above, I guess it's possible the noise starting around the same time could just be a coincidence. Stranger things have happened.

Vehicle is operating normally otherwise. Haven't noticed any issues with the drive, so with what y'all have said, I am less concerned that this is an immediate concern. Very much appreciate the insight!

 

One thing that can make a pump "noisy" without there being anything wrong with it: Low fuel level. With a low fuel level, the body of the pump is not 'muffled' in fuel.

Just a thought. Your "noisy pump" could just be a symptom of you need to put gas in it.

 

As I was reading up on this stuff, I saw that, so I filled it up. Not much change in the noise (maybe a tiny bit quieter?), so wasn't that, but appreciate the tip! When I get some time, I will try to open it up and actually take a look at it, see how it's mounted, etc. Like I said in a post above, I'm very new to working on my own car, but it seems like there's a youtube video (or a guide on this forum) for just about everything, so I'm trying to read and watch as much as I can. Enjoying learning about this stuff.