93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died too

[GunnyP]

93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died too

Battery warning light went on about 250 miles from home heading to NYC. In January installed new battery, new high-output 220A alternator all connected with 2/0 AWG welding cable with ANL fuses and additional engine and chassis grounds to eliminate possibility of just this occurring. It is a Northstar AGM 34/78 deep-cycle battery 880CCA.

Had DVM so checked alternator battery post to case and no output showed; only battery voltage. Alternator was 80 days old; $300 brick. Remembered had intended to change serpentine belts but hadn't done so. Middle of nowhere but found an O'Reillys. They had only cheap belts in stock. Luckily serpentine belts on 93 PAU did not involve the motor mount after all. New belts stopped a troubling rattle of the belt tensioner but still no alternator output. Cancelled business trip and limped the 4hrs home with all electronics off.

The old alternator had been working but as I keep high draw computers churning in the trunk off a power inverter it simply wasn't up to that task. Don't have a clamp meter but think it only put out 60A. I mounted it in hoping of getting back on the road. No go! It too suddenly has no output! In addition, Service Engine Soon lit up after a few minutes.

Grabbed the paper clip and jumpered the OBD1 but stupidly in my rush I turned the key past "On" and cranked the engine with the OBD1 jumpered. It was still flashing 12 when I realized my mistake and shut the engine off and carefully turned the key to the "On" position. It flashed out DTC codes 26 and 56 (Quad-Driver Module A & B Faults). I am hoping that was not because I cranked the engine with the OBD1 shorted. I removed the battery cables waited overnight and still the same codes appear.

I found a few posts indicating DTC 26 and 56 may be a short or open circuit issue. The QDM A seems indicate possible shorts on:

1.Canister Purge Solenoid
2. Temp Lamp
3. Low Speed Fan Relay
4. TCC (?)

Locating and how to check these for shorts? Do I find these components, remove them from the engine and use the DVM to check for continuity? I better get a piercing probe.

Haven't look into the QDM B yet.

More globally, could this have fried two alternators or should I be looking elsewhere? Merde, are my alternators fried or missing a signal from this 4-pin connector on the alternator? I just saw one YouTube video wherein a tech is looking for 400Hz output from the 4-pin connector. He is using a massive SnapOn analyser. Which pin? How do I assess this with my DVM?

Okay now I'm seeing videos discussing activating the alternator. It is maddening that activating the alternator is never discussed on any of the high view count videos. I've never even heard the word activating associated with the alternator and I've watched hundreds of these fracking videos. The videos talk about activating but don't show. How do I test for this activating signal on the 4-pin plug?


I've just ordered a 2 Volume Factory/Electrics Service Manual on eBay for the 1993 PA/LeSabre but another 3/27 until it arrives. So I'm dead in the water without some guidance.

Rather than wait for repair of the 80 day old, 220A alternator they allowed me to buy another one and return this non-working one. It should arrive soon but I dare not install it if I've an alternator killing machine. I've had the battery recharged. It is in good working order.

 

[HotZ28]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

You have a lot of problems which may be caused by a quad driver failure in the ECM. With that many faults, I would suspect that to be the problem. In addition, the ECM does monitor battery voltage to (excite) the charging process of the alternator. Did you have the alternators bench tested before condemning them?

 

[GunnyP]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

No. I haven't had them bench tested yet. Autozone, is saying that they can't bench test the high-output as they only test against regular specs. . I did "check the diodes" by setting the DVM to diode and measuring from battery post to case. That test seemed to say diodes working on each. In fact, I've done every test but this ""full-field test" wherein apparently one spoofs the regulator to demand full output.


The replacement HO alternator just arrived. So I have on hand both failed and replacement HO alternators as well as the original CS130 factory spec (it has a remanufactured tag on it). Whoops, forgot I had the original which Autozone can and (phone call later) just agreed to bench test. Heading down to have that done.

Thanks HotZ and I'll be back with bench test results on the latter.

 

[GunnyP]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

The re-manufactured stock CS130 passed the Autozone bench test!

So, I've a good alternator, good battery, new serp belts but no charging. Odds are the 220A alternator would also pass a bench test. It is the CS130 carcass with visibly thicker copper wirings within.

 

[MelsRegal]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

how about a hidden broken wire under the insulation in one of the connectors plugging into the alternator

 

[GunnyP]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

how about a hidden broken wire under the insulation in one of the connectors plugging into the alternator

Yes, it might be a broken wire; else, the ECM faults may mean a signal is simply not being sent to activate the alternator. There seem to be two wires attached to the plug. They disappear into a huge mass of wires impossible to trace into the firewall at all too short a distance. One wire ought to be the battery light on the dash and the other the actual signal wire from the ECM.

I must up my DVM skills and figure out how to properly determine whether a short exists. I'm thinking of trying to wire up a direct line from the battery to artificially provide the activation signal to the alternator that perhaps is not coming through the plug from the ECM.

I have to find out which of the four prongs looks for 12V and whether it actually is a full 12V or if I need to place a resistor in line to attenuate the signal to the appropriate level.

 

[GunnyP]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

There might be an alternator fuse according to this website that's been referenced by HotZ28 before although I am not finding any such fuse in the engine bay. Anyone know if the 1993 PA has one?

http://troubleshootmyvehicle.com/gm/3.8L/how-to-test-the-alternator-2#3

 

[GunnyP]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

Goals:
1. Confirm current 220A HO Alternator remains operable
2. If so, return just purchased 220A HO Alternator replacement as uneeded ASAP
3. Fix DTC 56 Faults
4. Fix DTC 26 Faults

Found this thread on a 1995 PA with similar circumstances of alt & battery passing bench testing but no charge
https://www.2carpros.com/questions/1995-buick-park-avenue-alternator-wont-charge

He jumpered the alternator plug which was showing 400mV with 12V and was able to charge the battery.


On my vehicle with only positive battery post connected, the L connection is hot showing 12.1V and the F connection cycles from 0mV to 400mV. I will use 18awg alligator clips to jumper 12V to the F connection to see if the alternator will activate. I've a test bulb with a 680ohm resistor which I'll place in the jumper path to reduce the voltage to the F connection as I'm fearful of overloading without a fused protection.

Apparently this fellow was able to trace the alternator's excite wire to a specific location on the wire harness. I hope to rectify the ECM situation later as finding this particularly wire amongst hundreds seems an impossible task.

 

[GunnyP]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

Goals:
1. Confirm current 220A HO Alternator remains operable


View attachment 11515

On my vehicle with only positive battery post connected, the L connection is hot showing 12.1V and the F connection cycles from 0mV to 400mV. I will use 18awg alligator clips to jumper 12V to the F connection to see if the alternator will activate. I've a test bulb with a 680ohm resistor which I'll place in the jumper path to reduce the voltage to the F connection as I'm fearful of overloading without a fused protection.

View attachment 11516

Eureka! Jumping the F connection is working. The DVM measures 14.8V from alternator case to B+ so the HO alternator is still functioning. I'll let it run to recharge the battery for 30 minutes.

Now have to fix the DTC 26 & 56 error codes.

 

[HotZ28]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

Now have to fix the DTC 26 & 56 error codes.

Good news so far! Since you have an OBDI ECM, all you have to do to clear codes is to disconnect the negative (-) battery cable for a few minutes.

 

[GunnyP]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

Good news so far! Since you have an OBDI ECM, all you have to do to clear codes is to disconnect the negative (-) battery cable for a few minutes.

Left neg cable off overnight. Codes were cleared prior to starting vehicle.

Removed OBDI jumper and started vehicle also re-attached SFLP 4-pin alt plug. SES light stayed lit and no alternator signal received at alt plug.

Jumpered OBDI again. DTC 26 & 56 codes displayed.

So I have to fix the source of the faults to make any progress.

 

[GunnyP]

Re: 93 PAU Alternator Dead, OBD1 Codes 26 & 56, Backup Re-man Alternator just died to

Oi! Success!

Unscrewed the bottom of the dashboard to get at the Relay Center to check the fuses there.


On my back shoving the tips of the DVM probes into the holes on the top of the fuses (and yes, just discovered one could do that). Lo and behold! The 15Amp ELRS Misc fuse was blown!

I grabbed a spare from the driver's side fuse box and popped it in. Started her up and alternator is receiving signal from ECM, battery is charging. With every bit of electronic gear on, alternator is holding at 14.65V on the alt case to B+. No SES light or other warning indicators at all.

Now, I've no idea what shorted this fuse out to begin with and won't feel comfortable until I at least know where all these various solenoids are located and their rhymes and reason. My factory/electronic service manuals should be here in a couple of days so I'll be well armed with knowledge before hitting the road again.

Thanks all for help!