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Resolved Question

Service Engine Soon - light stays on

Installed MSD 6AL Ignition Control and MSD Ignition Coil in 1991 GMC Sierra 5.7L engine. Engine starts easily, idles well, runs smooth but the light comes on immediately after starting and remains on.
Checked for OBD Diagnostic Trouble Codes but none are showing/registering; no flashes. Disconnected battery for two minutes to clear system. Restarted engine and light came back on and remained lit.
Spoke with MSD tech rep who stated he had no idea as to what the problem could be.
Owners manual states the "light" monitors operation of the emission control system and the vehicle needs to be serviced. But there are no Diagnostic Trouble Codes for reference.
Nearest GMC dealer is a five hour drive.
Appreciate advice on what to do, or where to start to correct this problem.
Thank you.

AKupNorth has chosen the best answer to their question. View answer
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All Answers

Best Answer chosen by AKupNorth

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Odd thought

In reply to: Service Engine Soon - light stays on

I know some automobiles produce this or similar alerts separate from "check engine" lights. It has to do with some scheduled maintenance interval and involves a sequence of steps. Usually, you need to turn the ignition switch to the accessory position and manipulate the gas pedal and/or odometer button. Some that use the gas pedal call for 3 full depressions within 5 seconds. I don't know that car but there's a chance focusing on OBD codes is just a tail chasing game. Good luck. Maybe someone will know the secret reset sequence that auto repair shops have in their documentation.

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yes

In reply to: Odd thought

might help to know the miles. Some do that every 30K miles for checkups.

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Reset Sequence

In reply to: Odd thought

Mr Haninger, I had no idea something of this nature might be in place.
Greatly appreciate the insight. That you. Will follow up and keep you folks posted.

Mr Denison, this rebuilt engine has less than 4000 miles on it but the factory "engine-computer" may not be aware if it.

Mr Proffitt, appreciate your input. It is appreciated. Will take a look at the reader you recommend.

Thank you gentlemen!

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sensors are what gives engine codes

In reply to: Reset Sequence

It's a matter of finding out which sensor. However, you say no codes given, so either they are hidden codes that only an OBD reader can see, or there's something wrong with the computer that takes the readings and turns on the engine service light. More likely a sensor problem though. When the engine was rebuilt, did they replace any sensors, like the oxy sensor on the exhaust manifold or exhaust pipe? Older models have only one, newer models have two.

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Sensors

In reply to: sensors are what gives engine codes

Mr Denison, my receipts show they replaced the Oil Pressure Sensor, Knock Sensor, Cooling Sensor, Temp Sending Sensor, Coolant Temp Sensor and Knock Sensor Connector.
Being in rural Alaska, there are so few of us they don't require vehicle inspections as they do in Anchorage, Fairbanks, etc.

Mr Proffitt, the OBD reader you recommended appears to be only for use on a vehicle newer than our 1991. It requires a 16 pin plugin, whereas our plugin is only 8 pins. Too bad for me. Will research further. Thank you.

Mr landdchamp, interesting you should mention the alternator. Yesterday afternoon when starting the truck, there was a new noise coming from around the alternator but it quieted down after a few minutes. Apparently (according to my receipts) they did not replace the alternator but the truck amp gauge is showing it to be putting out what appears to be a normal charge. Will check the items you have mentioned. Thank you. Always a pleasure to hear from you Loren!

Unfortunately, it has started snowing again, with a little over two inches so far; and still coming down. As soon as it lets up, will follow up on the recommendations that have been made.
Thank you gentlemen. Greatly appreciate the assistance.

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That's why I noted this needed checking.

In reply to: Sensors

OBD is a very big deal. Prior to standardization the diagnostics port was proprietary and often only readable by the maker and service centers authorized to have the gear.

That changed. Much for the better. Sorry to read your model doesn't have this.

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The one I always have problem with is;

In reply to: Sensors

...the gas tank purge sensor. It's the one that pumps a vacuum into the gas tank and then measures the time for the vacuum to bleed back down and if it's too quick, it means there's a leak somewhere in the gas fumes purge system (think old style charcoal filter can). There's an easy way to check that. Fill the tank to full, clear the codes by disconnecting the battery for a few minutes, then crank the car. If the engine light stays off for first 50 miles or so until the next engine startup, then that system has a leak in it. It's not detrimental to running the vehicle, just for those worried about a few fumes escaping and DESTROYING THE WORLD's atmosphere, LOL.

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I'm curious

In reply to: Reset Sequence

Is this needed to pass some state inspection? In Maryland we get that checked every two years. In Florida it's never checked, and many just drive with the engine light on. Best if corrected however.

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Trip/odometer Resset!

In reply to: Odd thought

Mr Haninger, could hardly wait to get back inside to share the good news.
Following your recommendation, turned the ignition key to the on-position (engine not running) and pressed the button/post to reset the trip/odometer to zero mileage. Turned the ignition key to the off position.
Then turned the ignition key all the way to start the engine. The service-engine-light came on briefly (normal) and then turned off (normal)!!!!
Turned the motor off. Repeated normal startup sequence with the same wonderful results! The light goes off as it should.
Can't thank you enough.
Amazing how such a simple "problem" caused so much aggravation.

I was really stumped on this one. Thank all of you for the kind assistance! Much appreciated.
From the Ol' Curmudgeon up North
Best Wishes for the coming year!

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Great to hear

In reply to: Trip/odometer Resset!

My daughter's Toyota does something like that and, on her car, I think it has something to do with the oil change interval. I'm surprised that, if your car is that old and you've owned it long enough, this hasn't already happened. It could be that if you take your car in for and oil change, the service people know to reset the countdown timer on it. I'm suspicious enough to think that these kind of things are a plot to get people to take their cars for dealer service where their mechanics have access to the secret codes to make these things go away. Thanks for reporting back.

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Answer
I'd get another OBD reading.

In reply to: Service Engine Soon - light stays on

Not all readers can get all the codes. Ask if some AutoZone will do this for you.

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Thank you, but........

In reply to: I'd get another OBD reading.

Appreciate the advice but I live in rural Interior Alaska and no AutoZone or other help available locally. Am using the truck's internal diagnostic system to "read" the Trouble Code, of which there are none. No flashes to count.
The system AutoZone uses, does it do more than read the equivalent of the flashes representing the Trouble Codes?
Your assistance is most appreciated. Thank you.

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How about Amazon.com?

In reply to: Thank you, but........

I picked up mine there. The bluetooth ones are under 20 bucks. You pair that with a smart phone and there you go.

Be sure to see if the 1991 has OBD. It's been around a while.

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No Cell Phone Service

In reply to: How about Amazon.com?

Living in the Bush results in no cell phone service. Subsequently no smart phone or bluetooth.
Our truck does have the OBD GM 2 Digit Trouble Codes and can be read by counting the flashes of the "Service Engine Soon" light. Have done so in the past.
Appreciate the help. Thank you.

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I got that covered.

In reply to: No Cell Phone Service

The no smart phone version I own and paid 27.99 total with shipping and taxes is this one.
https://smile.amazon.com/gp/product/B01G5EA74I/

It's for the reason above. Not all OBDs read all codes.

In your case it's time to get the OBD reader. Borrow, buy, etc.

It's sometimes inevitable that you need the right tool. Or sometimes it's something that only the maker or dealer can fix. Annoying to hard core DIY folk which I count myself as one.

I like Steven's idea bout maintenance. Check your manual for any maintenance reset feature. I have to know this for one of my cars since the local oil change place didn't know my model.

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Answer
Service Engine Soon Lamp

In reply to: Service Engine Soon - light stays on

Hi, AKupNorth; Check the alternator and ECM2 fuses. (just for grins, check all of the fuses)
Loren

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Answer
Service engine light stays on.

In reply to: Service Engine Soon - light stays on

I had similar problem. I put a can of SEAFOAM in gas tank. Disconnected battery for 5 minutes and restarted the car.
It works good until wintertime when gasoline changes the grade/quality.

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SEAFOAM

In reply to: Service engine light stays on.

Not familiar with product. Will have to research.
Thank you.

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Answer
AKupNorth

In reply to: Service Engine Soon - light stays on

Hi, Gus, and welcome to the CNET auto forum. Has been a long time! Is this the same truck you had that had the headlight switch issue? Anyway, glad to see you here. Lots of knowledgeable guys, here.
Loren

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Same Truck

In reply to: AKupNorth

Yes Sir, same truck.
May also be having a problem with the brakes, but subject for another post.
Best Wishes

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Brakes

In reply to: Same Truck

Hi, Gus; And don't call me sir! LOL When you mentioned brakes; Brake fluid draws moisture like a sponge. Where you live, you should have it flushed every 2-3 years. Just FYI.
You, SIR, have a great week. You have earned the "Sir"!
Loren

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Flushing Brake System

In reply to: Brakes

Hi Loren,
Thank you for the kind thoughts.
Had no idea it is good to flush the system so often up here. Appreciate the advice.
Hope to get back to work on the truck Monday.
Wind has been too strong (45/50mph) to safely work with the engine-compartment hood up. Not to mention the windchill factor; heh, heh.
Will keep you folks posted regarding progress.
Best Wishes

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