Regal Posted August 30, 2022 Report Share Posted August 30, 2022 This is for a 1993 Buick Regal Limited coupe. Perhaps I should have asked around here earlier but here goes. Some time ago, after having just replaced a fusible link and having good charging again; I'm just accelerating from a green light and all is good one second. A second later the car just goes gutless and the check engine light comes on. I borrow a good OBDI&II scanner and receive some codes; DTC 56 displays first, along with a few others mentioning high TPS and a few other issues including transmission shift fault and cruise control vacuum solenoid (a known issue). But the "prominent" code seems to be "DTC 56 - Driver quad "b" module." So this begins my replacement of several parts. I really am unfamiliar with the particularities of OBDI, so begin to replace the least expensive of parts I think it could be; the first being the TPS sensor. After installing the US made Integrated Controls TPS sensor, I obtained a Japanese made AC Delco OEM NOS MAF sensor and installed it. Still nothing. Now in this process I had also ordered and had on hand already a US made NOS Delphi "Factory Authorized Refurbished" PCM. I have since replaced this, and that same night charged my AC up and now with the AC on have the compressor running full time (as opposed to consistently cycling) which is a first in 3 years owning this car. With these new sensors and engine computer the damned thing idles like it just left the factory now, yet my check engine light remains and is a dog from a stand still. I am at the point where I think I should replace the 1-2 and 2-3 shift solenoids in the 4T60E. Does this sound like the right path to take at this point? I mean, the car does seem to be almost in a "limp mode" as if it's not in first gear. If I select 1st manually it does seem to drive with the regular gusto I had been accustomed to. I guess I should have looked here first but used it as an opportunity to replace a bunch of old parts with GOOD new ones before dropping the transmission pan and having to replace a bunch of good Amsoil fluid and a NOS Wix filter I won't find another of. Funny enough the fuel economy has been terrific. I could get 350 miles out of a full tank, and now after replacing these sensors and whatnot it seems like this could raise even more. It's half tempting to not "fix" it and leave it as is for the economical driving. I've been driving it like this so long that when it is finally fixed it will feel like a new car I am not familiar with! I just hope driving it hasn't caused other damage (other than brake pads possibly wearing out quickly) but I don't think so. Also, if I do replace those shift solenoids can I also replace the TCC solenoid (same part as the other two) as well as the TCC pulse width modulation solenoid (looks like more of a valve with a 90 degree angle if I recall) without having to tear the transmission apart more? Quote Link to comment Share on other sites More sharing options...
Schurkey Posted August 31, 2022 Report Share Posted August 31, 2022 Connect a scan tool, look at the data stream. Verify ALL sensors and computer outputs. Verify that the prior codes have cleared, and no new codes--including for the transmission--have set. Verify fuel pressure. How old are the usual "tune-up" parts? Spark plugs, plug wires, air and fuel filters, etc. Quote Link to comment Share on other sites More sharing options...
Regal Posted August 31, 2022 Author Report Share Posted August 31, 2022 (edited) Previous owner had tuneup done in shop in 2018 from what I recall from the service records. Those items look fine and mileage wise they're not really due for replacement. I've replaced the typically more neglected things like TPS, MAF, PCM etc. and the motor runs very smoothly at idle and the throttle response with no load in Park seems sufficient also. The new computer might have cleared the old codes but I'll need to borrow a code reader again to confirm what's showing up now. The check engine light came back on about 10 seconds after starting the motor with the new PCM. Weirdly I am happy with the throttle response (at least in park haha), just not the power that's being output. I'm totally sure at this point it is the shift solenoids needing replacement based on the code DTC 56. What I want to know is if the TCC and PWM solenoids can also be replaced at the same time when the pan is dropped and the filter out? Edited August 31, 2022 by Regal Quote Link to comment Share on other sites More sharing options...
Schurkey Posted September 1, 2022 Report Share Posted September 1, 2022 "Code readers" are a hateful consumer-grade waste of time, money, effort and enthusiasm. Get a real SCAN TOOL, and look at the data stream. "Codes" can be useful. The real information is in the data stream. What is the fuel pressure? Quote Link to comment Share on other sites More sharing options...
Regal Posted September 1, 2022 Author Report Share Posted September 1, 2022 It was an older Innova "OBD I & II" model. Not sure if it was a "code reader" or "scanner" to be honest. Quote Link to comment Share on other sites More sharing options...
mechanic58 Posted September 9, 2022 Report Share Posted September 9, 2022 Have you checked all of your grounds? This sounds like a bad ground issue to me. Quote Link to comment Share on other sites More sharing options...
Regal Posted October 15, 2022 Author Report Share Posted October 15, 2022 This issue has finally been resolved, and it took so long because I never suspected my new alternator was faulty. Only when it fully gave up the ghost and was replaced did the DTC 56 code clear. Several sensors and the ECM were replaced; and others were about to be as I had bought them already.. anyhow with all the new parts installed and finally with the new alternator; the car is running and driving great! Quote Link to comment Share on other sites More sharing options...
GTP091 Posted October 16, 2022 Report Share Posted October 16, 2022 Interesting source of the problem. Glad you found it. These vague issues are always a huge win when you get it sorted out. Regal 1 Quote Link to comment Share on other sites More sharing options...
Regal Posted October 24, 2022 Author Report Share Posted October 24, 2022 (edited) On 10/16/2022 at 9:25 AM, GTP091 said: Interesting source of the problem. Glad you found it. These vague issues are always a huge win when you get it sorted out. There was also a 10 amp fuse replaced, but I am not sure which one it was. I was told it could have happened after the alternator finally gave up but am not really sure. I doubt a 10 amp fuse alone would have caused those issues I has having. The voltmeter always looked good so I never suspected the alternator; perhaps it was not putting out the right amperage or some other issue existed with it. Edited October 24, 2022 by Regal Quote Link to comment Share on other sites More sharing options...
primergray Posted December 6, 2022 Report Share Posted December 6, 2022 Check that aux terminal post too...although your year might not be as prone to issues. I had a lot of charging issues until I replaced the zinc aux terminal on my 94 with the brass one, like so: https://www.impalassforum.com/threads/replacing-the-auxiliary-battery-post.237690/page-3 Quote Link to comment Share on other sites More sharing options...
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