My 95 is mad at me for neglecting it

[premiumV]

I had a bad coolant leak in late June and just now got around to replacing the crossover manifold/water pump housing gaskets. It ran good when I parked it and the following symptoms are both right before and after the coolant leak repair. I know I need to find a scanner but what the heck can cause so many seemingly unrelated problems?

The engine won't start or show any signs of life. I did get it to run on its own by using starting fluid but it sounded bad like only some of the cylinders were firing.

The radiator fans are on constantly.

"SES" and "Traction Off" lights are always on. Switching the traction button doesn't make the light go out.

No low coolant alert when the tank is low, it worked when I parked the car in June. No parking brake alert, no door ajar alert. Not sure if these will work when the engine is not running but I thought they did.

The outdoor temperature and set temp blinks for a while but eventually stops after a few minutes.

Not related but my front speakers and bass channel are gone. When it rains it pours. :-(

[premiumV]

So I looked at the car today not really sure what to do. I thought about just leaving the ignition on for a few hours but the cooling fans draw a lot of current so I pulled the 60A fuse. I noticed that all of my warnings on the DIC started working again. I gave the engine a crank and it started right up and ran smoothly but at 1600 rpm's. I let the engine get up to operating temp, put the fan fuse back in and finished topping off the coolant. Switched the engine off but it wouldn't start again until I pulled the fan fuse. I still have the "SES" and "Traction off" lights and I have a Tech I scanner with the correct connector from a buddy on the way. I feel so much better from not being so overwhelmed with weird problems.

[premiumV]

It looks like I need to replace the PCM. Any cautions about buying one for a 95 autobahn? I see a lot of them on eBay for a reasonable price.

I finally got the Tech1 scanner but it wouldn't connect to the PCM, however it did connect to the chassis and body modules. I did the power and ground checks to the PCM and also determined that the PCM is holding the high speed cooling fan relay on. Since the factory Bose stereo amp also quit working, and both are hot with the ignition off, I'm thinking a voltage spike may have damaged the units. I had a Genius G3500 so-called smart charger connected since I parked the car in June. The best place to connect a charger is right at the battery for the best filtering but my doors are too tight for the power cord to exit and it's so convenient to hook it up in the engine compartment which I did. So this charger has an automatic desulfation cycle which outputs high current/voltage pulses. I looked up the manual online to read more about it but I happened across the updated revision of the same model. This revision has a manual button for the desulfation cycle and also a warning about disconnecting the battery to protect electronics. To me, a change like this means that they had damage problems with the original design. If I had hooked up right at the battery my electronics may have been saved. Another thought is we had some very close lightning strikes a few months back that could have induced voltage into my extension cord going to the charger but the charger is still working OK.

[tigger]

Nov 17, 2020 15:21:36 GMT -6 premiumV said:

It looks like I need to replace the PCM. Any cautions about buying one for a 95 autobahn?

Autobahn and non autobahn PCMs are NOT interchangeable! If your Aurora Is an autobahn, it'll work fine. If not, you need a regular Aurora PCM.

[premiumV]

OK, thanks for that info.

[aphex]

Does the car cranks and at normal speed?
Battery charged up on a wall charger and does it hold charge? I know I can't get my battery to charge from the engine bay so I'd actually remove the battery from the back and put a couple bolts in it to get it charged up. That's what I have to do. Doing this will give the car time to shut down and do a full reset, and come back fresh. Which is an old trick that brings back shorted stereos and sometimes fixes/brings back problematic infotainment systems on newer cars. I wouldn't go chasing the PCM yet, if you haven't already.

[premiumV]

The battery is in good shape. I have been retired for a few years and had a good ole Battery Tender brand on it intermittently and never had any charging issues. The charger would cycle and eventually turn green for trickle. Since the car was going to sit for a few months before working on the coolant leak I switched chargers for no other reason than the Genius has a lower profile allowing me to close the hood and I moved the Tender back to the mower. I had the battery disconnected for about 2 weeks while I was repairing the coolant leak and also when I was fooling with the PCM in the vehicle. I fired up the PCM on my electronics bench and it acts the same way there including no communication with the GM Tech1 scanner. I did notice that the coolant fan output signal isn't shorted. It was open while the PCM was booting up and then went to ground which seems odd, like the programming may be messed up. This is with a resister on the coolant temperature sensor input simulating about 50 degrees F coolant temp. I do have a PCM on the way and I was fortunate enough to find a PROM module with the same letter code as mine just in case that is the problem. If the battery + also feeds the PROM, and I had a voltage spike on that lead, that may be the problem.

Reference for others reading this post. On the 1995 year, I found out the PCM's are all identical. The Autobahn and some other options are in the PROM. 1996 and up, the PROM is not removable and you would need an Autobahn PCM if you have that option or find someone who can reprogram the PROM to match your car.

Nov 24, 2020 11:05:13 GMT -6 aphex said:

Does the car cranks and at normal speed?
Battery charged up on a wall charger and does it hold charge? I know I can't get my battery to charge from the engine bay so I'd actually remove the battery from the back and put a couple bolts in it to get it charged up. That's what I have to do. Doing this will give the car time to shut down and do a full reset, and come back fresh. Which is an old trick that brings back shorted stereos and sometimes fixes/brings back problematic infotainment systems on newer cars. I wouldn't go chasing the PCM yet, if you haven't already.

[premiumV]

I installed the used PCM and everything is back to normal except for the sound system and one other thing. The PROM was already installed in the replacement PCM so I checked it that way first. That worked good so I replaced the PROM with my original PROM and that also worked so I'm leaving the original installed. The only DTC code left in the PCM is the "throttle sensor calibration not finished" which can be done with the Tech1 scanner tomorrow.

Has anyone heard of DTC 074C which is "real time clock not working" and is it mentioned in the FSM somewhere? I couldn't find it. My date and time in the DIC is just a bunch of lines and I can't program it. It was like this when I first noticed that the car wouldn't start so probably another thing that got toasted. I don't plan on fixing it unless it's simple but I'm curious where the RTC is located.

[premiumV]

Late Post, fix is at the end

Getting rid of the idle learn incomplete code and high idle wasn't a simple task. The fix was simple but it took a lot of time to find. I had a huge backfire while first trying to start the car before I knew that the PCM was bad so I spent a lot of time on a possible vacuum leak. The FSM troubleshooting tree also pointed to a vacuum leak. If no vacuum leak it said bad PCM as the last step. I thought for sure that the backfire flap opened up and didn't close properly from being old. I used an unlit propane torch on the flap and everywhere else on the manifold and vacuum lines and couldn't get a response. Thinking it could have blown a gasket or cracked the manifold underneath I placed a plastic peanut can top over the intake of the throttle body. It sucked it right out my hand when it got close and the car immediately stopped, and I couldn't remove the top for about 5 seconds because it was being held so tight by the residual vacuum.

Pretty sure no vacuum leak, I removed the throttle body again to clean the IAC motor which is only on the 95' cars. Not much carbon in it and the grease was dry so I greased it and put it back together. I had cleaned the bore of the throttle body sort of rushed when I replaced the coolant crossover gaskets so I took it inside this time to the well lit bench to give it a good look. The FSM also mentioned replacing the throttle body as a step for high idle. On the side of the TB there is a mechanical factory adjusted stop and I noticed that the throttle plate linkage was about an 1/8th of an inch from touching that mechanical stop. I thought for sure that I had finally found the problem. So I blocked the throttle plate open so I could inspect it, thinking the backfire might have distorted it. It looked nice and straight but I noticed a ton of carbon buildup on the edge of the throttle plate. I cleaned it off and the throttle plate linkage now hit the mechanical stop. I was less sure the problem would be gone because of carbon and it wasn't. Exact same high idle speed an no idle learn.

So I was going to contact the seller and see if he had another PCM. It's guaranteed for a year so I could send mine back. I still had the Tech I connected so I decided to go through every single engine screen as a last resort to see if something stood out, there must be about 100 screens. I got through "engine 1" and nothing looked out of place. Almost finished with "engine 2" and I saw something odd but didn't know what it meant. Servo, expected value 0%, actual value 26%. I have wasted so many hours looking for things in the poorly laid out FSM but I finally found that servo was the cruise control. The FSM didn't say, but I assumed that something was pulling the CC piston out of position, like maybe the throttle spring. Then I found a "CC cable slack adjustment" Remove CC cable from CC piston. Fully retract the IAC motor plunger with the Tech I. Reattach the cable in a hole with minimum slack but not too tight. I had to go 1 hole looser than the factory position???

Boom!!! Normal idle speed and the idle learn completed immediately shutting off the SES light. I felt like punching myself in the nose. So what happened is, there is actually a "CC cable slack value" stored in the PCM. The FSM has tons of info if you can only find it. When the PCM is replaced the new PCM sees that the mileage has changed, assuming a new vehicle, and resets all of the "learn procedures" to factory default. If I had driven on a highway and accidently done the CC slack learn, which is, accelerate to about 50 mph on a straight road, take foot off of accelerator for at least 3 seconds, push CC set speed button. The PCM would have seen that the cable was too tight and adjusted it for more slack. But then I wouldn't have known why my car magically fixed itself. I actually felt the 2 cables at the throttle body a few times to see if they were too tight, but I failed to check them when I had the IAC plunger manually retracted. 

[tigger]

Good to hear you got it squared away!

And special thanks for following up with your troubleshooting process and repair solution!

[premiumV]

Jan 26, 2021 16:14:01 GMT -6 tigger said:

Good to hear you got it squared away!

And special thanks for following up with your troubleshooting process and repair solution!

You're welcome. This forum sure has gotten slow compared to 15 years ago. I guess there are not many Aurora's on the road anymore.

[premiumV]

I finished repairing my BOSE amp and it was a mess inside. I can now say with 100% certainty that the damaged PCM and amplifier were knocked out by a very close lightning strike and not the automatic desulfation mode on the charger. I have seen a lot of lightning damage in my electronics career and I recognized it right away when I opened the amp. I knew the amp had 3 always energized battery hots but I didn't know that they went to a relay inside of the amp that only gets actuated when the radio is turned on. That takes the battery charger out of the picture because there was no 12 volt source to any of the amp electronics. Four of the six channels were blown and one of the amplifier IC's exploded and had a small fire. The driver side rear speaker was also blown because of melted voice coil wires. The driver front speaker and amp channel may have been spared because the wire(s) in the door boot have been broken for some time.

The first thing wrong that I noticed were my cooling fans running when the ignition switch was turned on. My theory now, is that everything with large coils of wire picked up the lightning energy. The cooling fan motors most likely took out the PCM and the speakers got the amplifier. The extension cord to the battery charger draped over the front fender, with the excess length coiled on the ground, probably energized the car body which started the mess.

Would anyone happen to have a spare rear Bose speaker for a 95' for sale? I'm not having any luck finding one.

Attachments:

[premiumV]

Can't believe I let this happen again. Turned the key on and heard the cooling fans running, OD temp display blinking, no start. The same indications as when the first PCM blew. At least I don't have to go through the extensive troubleshooting again, just buy another PCM.
I normally disconnect the extension cord to the charger when a storm is coming but missed this one. I heard a static crash on my computer speakers and then loud thunder about a second later. I thought this strike might be far enough away but nope.
The stereo amp was spared this time.

[AuroraGirlFromMars]

Jun 7, 2022 14:41:52 GMT -6 premiumV said:

Can't believe I let this happen again. Turned the key on and heard the cooling fans running, OD temp display blinking, no start. The same indications as when the first PCM blew. At least I don't have to go through the extensive troubleshooting again, just buy another PCM.
I normally disconnect the extension cord to the charger when a storm is coming but missed this one. I heard a static crash on my computer speakers and then loud thunder about a second later. I thought this strike might be far enough away but nope.
The stereo amp was spared this time.

you may want to invest in some surge things

[premiumV]

Jun 7, 2022 19:27:09 GMT -6 AuroraGirlFromMars said:

Jun 7, 2022 14:41:52 GMT -6 premiumV said:

Can't believe I let this happen again. Turned the key on and heard the cooling fans running, OD temp display blinking, no start. The same indications as when the first PCM blew. At least I don't have to go through the extensive troubleshooting again, just buy another PCM.
I normally disconnect the extension cord to the charger when a storm is coming but missed this one. I heard a static crash on my computer speakers and then loud thunder about a second later. I thought this strike might be far enough away but nope.
The stereo amp was spared this time.

you may want to invest in some surge things

I think you're right.

[fredwinterburn]

Sorry to hear it happened again. You are a far more patient man than I am. I also live in a lightning prone area on a rural line that seems to pick up every lightning strike. This is a good lesson for me not to use a battery tender except in the winter. High voltage can do strange things as you'd think connected across a battery that the battery would provide a low impedance short for the lightning strike. But nope!  

Jun 7, 2022 14:41:52 GMT -6 premiumV said:

Can't believe I let this happen again. Turned the key on and heard the cooling fans running, OD temp display blinking, no start. The same indications as when the first PCM blew. At least I don't have to go through the extensive troubleshooting again, just buy another PCM.
I normally disconnect the extension cord to the charger when a storm is coming but missed this one. I heard a static crash on my computer speakers and then loud thunder about a second later. I thought this strike might be far enough away but nope.
The stereo amp was spared this time.

[fredwinterburn]

Looks like the first generation Aurora could use some high voltage protection. Lightning is about as bad as it can get, but not insurmountable for indirect strikes. Lots of options including spark gaps and MOVs. TVS diodes maybe? They make back to back TVS diodes that will conduct in either direction. Even lowly resistors and capacitors strategically placed might be enough. Ya gots me thinkin! I wonder if more modern cars have improved that sort of protection. I would presume they have. Years ago a friend of mine witnessed a car struck by lightning. 3 of the 4 hubcaps blew right off, but that was in the days before cars were full of sensitive electronics.  Fred

[premiumV]

Jun 8, 2022 15:50:48 GMT -6 fredwinterburn said:

Looks like the first generation Aurora could use some high voltage protection. Lightning is about as bad as it can get, but not insurmountable for indirect strikes. Lots of options including spark gaps and MOVs. TVS diodes maybe? They make back to back TVS diodes that will conduct in either direction. Even lowly resistors and capacitors strategically placed might be enough. Ya gots me thinkin! I wonder if more modern cars have improved that sort of protection. I would presume they have. Years ago a friend of mine witnessed a car struck by lightning. 3 of the 4 hubcaps blew right off, but that was in the days before cars were full of sensitive electronics.  Fred

The problem is that I'm not 100% sure of the electrical path that is causing the damage. The first time which was a much closer strike, almost every output amplifier in the Bose amp in the trunk also blew. The 12 volt input to the amp goes through a mechanical relay which only closes when the radio is turned on. After seeing that, my theory was that the extension cord laying on the ground is picking up energy and transferring it to the body. Anything with a coil of wire, like the speakers and cooling fans is transferring that energy to the electronics. On both strikes nothing in the house was effected at all. Lights didn't change and the computer UPS didn't beep which is very sensitive.
I'm now searching for the 3 large PCM connectors with cut wires which will make it much easier to troubleshoot the 2 PCM,s and find out what is being damaged which will show me the path. A solar charger may be a better solution so I can get rid of the cords which are kind of a PITA. BTW my Jeep is on the same cord and I haven't had any problems with it but it has more basic electronics.

[fredwinterburn]

Maybe charging closer to the battery would make a difference. Rather than charging at the positive cable end under the hood, pull the back seat bottom and charge directly to the battery positive terminal and a nearby ground. I just can't see how the coils in motors and relays could be energised by radiant energy from an extension cord feeding a battery charger, even with the energy of a lightning strike. What is happening is high voltage passing right through the battery charger into the 12V system directly. Years ago I did have an EMP from a direct hit of lightning on my TV antenna tower that turned on a battery operated toy in an adjacent room, (and really lucky the house didn't catch fire), but what is happening with your car is much more than EMP.  I think it's more likely that with the long path back to the battery from the +tve battery cable that capacitive coupling through the insulation to ground is what is causing the high voltage being transferred to sensitive loads. Same effect as laying two ignition wires side by side for a few feet, and the induced voltage could easily be of the wrong polarity which would further damage electronics. If charging right at the battery, the long cable is much less likely to capacitively couple with ground during a high voltage event. In other words, it won't turn the car body into one plate of a high voltage capacitor (the long +tve battery cable being the other plate). Most of the voltage spike should then be safely snubbed by the battery. Fred 

Edit: Another point I forgot to mention is that it takes very little inductance to prop up and maintain a high voltage spike. Which is why suppression devices are located near the point of suppression and have short leads (ignition condenser on the old Kettering system being an example). The 6 or 8 feet of +tve battery cable running forwards in the Aurora has enough inductance that the battery can't effectively snub a very fast rising, high voltage pulse. Add that to the capacitive coupling I mentioned, and that cable/ground becomes a high voltage 'battery' for just long enough to be dangerous. And as I mentioned it could be the wrong polarity so devices without good reverse polarity protection are more vulnerable. Once again, just my theory.  

[premiumV]

Thanks for your input Fred. The first time it blew I was charging at the engine. The car wasn't derivable at the time because of a major coolant leak and I stuck a charger on it for a few months until I took care of the leak when the weather cooled down. I had 2 different chargers on it but I don't know which one was on it when the strike came. One was a Battery Tender which has a transformer. The other was a sealed NOCO with a switching power supply. After I finished the repair and replaced the PCM, I installed the Battery Tender inside hooked up directly to the battery and it blew again. After the second failed PCM and before my new posts here I decided to buy another NOCO (using the weatherproof NOCO on the Jeep) because I think a switching supply would be be less prone to voltage spikes than a transformer supply.

So why did the amp blow when the 12 volts was disconnected by the relay? The amp has ground, audio signal wires from the radio, power relay coil wire from radio, and wires to the speakers. My career was electronics and I have seen a lot of lightning damage. The inside of the amp had classic signs of lightning damage with burns and open traces at the point where they change direction.

[fredwinterburn]

Maybe the high voltage jumped the relay contacts. Burnt at the corners eh? Makes sense since high voltage loves to travel in straight lines.

Jun 9, 2022 10:03:34 GMT -6 premiumV said:

Thanks for your input Fred. The first time it blew I was charging at the engine. The car wasn't derivable at the time because of a major coolant leak and I stuck a charger on it for a few months until I took care of the leak when the weather cooled down. I had 2 different chargers on it but I don't know which one was on it when the strike came. One was a Battery Tender which has a transformer. The other was a sealed NOCO with a switching power supply. After I finished the repair and replaced the PCM, I installed the Battery Tender inside hooked up directly to the battery and it blew again. After the second failed PCM and before my new posts here I decided to buy another NOCO (using the weatherproof NOCO on the Jeep) because I think a switching supply would be be less prone to voltage spikes than a transformer supply.

So why did the amp blow when the 12 volts was disconnected by the relay? The amp has ground, audio signal wires from the radio, power relay coil wire from radio, and wires to the speakers. My career was electronics and I have seen a lot of lightning damage. The inside of the amp had classic signs of lightning damage with burns and open traces at the point where they change direction.

[premiumV]

Could be. I couldn't tell any time difference on the first strike, seemed instantaneous. Never did see where it hit. Second strike was about 1 second apart. I'll buy another NOCO and add some protection.

Thanks!

[premiumV]

Back on the road again. I replaced the blower motor while the old PCM was removed but not sure if it gave me any more working room. I still have an annoying intermittent (mostly there) problem to take care of. It started after I replaced the cooling crossover gaskets, I believe from stretching a large wiring harness to get the crossover out. Parking brake on, low brake fluid, oil level sensor fault, low oil level. All of these show up at once and the chime is dinging constantly. Pulling the chime fuse disables the gauges and doesn't track fuel usage so I had to put it back in.

[jimrockford007]

I'm telling you what it has been a long time since I have seen somebody posomebody post a thread up like this to where they go through their detailed troubleshooting procedures and their testing things and figuring out the the theory of operation of an electronic component versus just condemning it and throwing it in the trash and buying a new Chinese piece of ******* congrats on all of your troubleshooting you get my award for car guy the month

[premiumV]

Jun 11, 2022 18:15:10 GMT -6 jimrockford007 said:

I'm telling you what it has been a long time since I have seen somebody posomebody post a thread up like this to where they go through their detailed troubleshooting procedures and their testing things and figuring out the the theory of operation of an electronic component versus just condemning it and throwing it in the trash and buying a new Chinese piece of ******* congrats on all of your troubleshooting you get my award for car guy the month

Thanks for the nice compliment Jim. The more fine details that are posted the more it will help others with a similar problem. Especially that stupid cruise control cable that was adjusted too short when I replaced the first PCM. I wasted sooo much time figuring that one out.

I have always been like this because it feels wrong to discard something that I know can be fixed and I enjoy the quality of older stuff. One of my oldest items is a 1966 Toro mower that still starts and runs like new. My father bought it when I was around 11 but one of my chores was cutting the grass so I have been the user all of its life. The quality HVAC blower I just replaced will not be discarded. A quick power up on my bench told me that the brushes are just worn out and I'm sure I can find some that will fit. My back is screaming never again but I will fix and put it on a shelf to collect dust rather than throwing it away.

[fredwinterburn]

Car guy of the month for sure. Not too many of these cars left where I live in southern Ontario. I haven't seen one other than my own on the road in years and I've been looking closely. I think they are worth every little bit of extra work if you can do it. Book value means nothing except to insurance companies. Fred

[AuroraGirlFromMars]

Is this car not used often? Is that why its left on a tender? You may considering installing a shut off, and buying AGM batteries. You can not touch them very often and as long as you fully turn the draw off you wouldnt have much discharge. When I say you can neglect it for a long time im talking months without using, as long as each use has a sufficient time for your alternator to operate, it wouldnt be too bad. 1g doesnt have battery load management I do not think so you wouldnt have any PCM or BCM denying the alternator from charging it would just do its thing.

With out turning the loads off, however, I suspect youd want to be charging the battery somewhere in 4-6 months for sure