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Topic: The service engine soon light is on..how do you check the codes?

in Forum: C4 Cooling and Heating Systems


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Re: The service engine soon light is on..how do you check the codes? (5/15)
 8/18/12 2:11am
davep85c4
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CaledoniaBrian said:
btw..it should always start with a code 12...this simply means the ECM has gone into diagnostic mode.

Yes, it should always display Code !2.  But Code 12 really means "No distributor reference pulses received".

 Because the engine is not running, there are no reference pulses, and Code 12 displays. When engine is not running, and NOT in diagnostic mode, CEL is lit solid. Like it would be for any other soft-code. A soft code is one that turns off the light when the conditions to set the code cease to exist. Start the engine, and reference pulses ARE received, and the "Code 12" goes away, and the light goes out.

The light is always lit with the key on, engine off. Because there is always a Code 12 in this state. Short A&B to enter diagnostic mode, and the light flashes the code.  That's what indicates you've entered code-retrevial mode: The flashing CEL.

|UPDATED|8/17/2012 11:11:16 PM (AZT)|/UPDATED|
Re: The service engine soon light is on..how do you check the codes? (6/15)
 8/18/12 9:10am
CaledoniaBrian
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1988 Convertable


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DaveP85C4 said:
CaledoniaBrian said:
btw..it should always start with a code 12...this simply means the ECM has gone into diagnostic mode.

Yes, it should always display Code !2.  But Code 12 really means "No distributor reference pulses received".

 Because the engine is not running, there are no reference pulses, and Code 12 displays. When engine is not running, and NOT in diagnostic mode, CEL is lit solid. Like it would be for any other soft-code. A soft code is one that turns off the light when the conditions to set the code cease to exist. Start the engine, and reference pulses ARE received, and the "Code 12" goes away, and the light goes out.

The light is always lit with the key on, engine off. Because there is always a Code 12 in this state. Short A&B to enter diagnostic mode, and the light flashes the code.  That's what indicates you've entered code-retrevial mode: The flashing CEL.


 

Thanks...makes total sence, and you are right of course.




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Re: The service engine soon light is on..how do you check the codes? (7/15)
 8/18/12 11:04am
TEN A C
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It's the wierdest thing.  I checked under the dash and I don't see anything that looks like the plug in.  I know on other cars when you get the emisions tested they use the plug in.  My 85 seems to be missing that port.  Is it possible that it's been relocated?  I took the plastic piece down from under the steering column and I don't see anything.

Thoughts?
Re: The service engine soon light is on..how do you check the codes? (8/15)
 8/18/12 11:09am
CaledoniaBrian
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Driver's side.....to the right....under dash. There may be a plastic cover on it that will pull off. I'm sure it's there.


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Re: The service engine soon light is on..how do you check the codes? (9/15)
 8/18/12 4:28pm
TEN A C
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Whew, okay, I found it.  Someone had tucked it way up inside under the dash area.  The code I get is 43....it flashed the 1 then 2....then it flashed 4 then 3...
 
Is this an urgent issue?  what does it mean and can it be fixed or do I need to do something myself to the care.
 
Thanks for your patience....I'm new at trying to fix this car....I can't do everything, most things, but it's helpful to know before I take it to a mechanic.
 
Thanks
Re: The service engine soon light is on..how do you check the codes? (10/15)
 8/18/12 5:06pm
CaledoniaBrian
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1988 Convertable


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OK, now you have somewhere to start.......if you google obd1 gm codes you should find a list of code numbers and what they stand for.
 
 
code 43 = knock sensor or electronic spark control circuit fault
below copied from another web site: remember google is your friend
...............................................................................................................................................
.

CODE 43

Trouble Code 43 indicates that there may be a malfunction in the Electronic Spark Control (ESC) circuit.

ESC is used to sense spark knock (pinging) and retard the timing to eliminate it. A knock sensor (located at the rear of the engine block) sends signals to an ESC module which then signals the ECM that knocking is being detected. The ECM will retard the timing by as much as 20 degrees in 1 degree increments. A loss of knock sensor signal or loss of ground at the ESC module will cause the signal at the ECM to remain high. The ECM will act as if no knock is present, and may possibly result in engine damage, if there is detonation.

Loss of the ESC signal to the ECM will cause the ECM to constantly retard the timing to its maximum. This results in sluggish performance and a Code 43.

The conditions for setting this code are:

  • Engine is running
  • ESC input signal has been low more than 2.23 seconds


Typical causes for this code include:

1) Open or shorted knock sensor
2) Loose knock sensor
3) Excessive mechanical noise within engine
4) Improper or incorrectly installed PROM or CALPACK in the ECM or defective ECM
5) Intermittent open in the EST line to the ignition module

 


|UPDATED|8/18/2012 2:06:49 PM (AZT)|/UPDATED|


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Re: The service engine soon light is on..how do you check the codes? (11/15)
 8/18/12 5:16pm
TEN A C
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Yep, I did Google it, I found that information but I don't know what it all means...is this something that I can replace or do I need to take it to a mechanic to have the knock sensor replaced?
 
Have you ever had this problem before?  If so, how did you fix it?
Re: The service engine soon light is on..how do you check the codes? (12/15)
 8/18/12 7:58pm
CaledoniaBrian
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1988 Convertable


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Posts: 150

  If you are not sure what they are talking about then I would suggest having someone that does have a look. It may be a lot of things....but most likely I would suspect the the module is shot.... But that is just a guess.
 If it was my car, I would have it looked at..... and knowing what you already know you are ahead of the game.
 
 


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Re: The service engine soon light is on..how do you check the codes? (13/15)
 8/18/12 8:28pm
TEN A C
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Thanks for all of your help.Smile
Re: The service engine soon light is on..how do you check the codes? (14/15)
 8/18/12 8:55pm
martone_1
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The knock sensor on your 85 is the same place as on my 85 right in front of the starter behind the exhaust manifold it can be reached if you lift the car on the passenger side about a foot with the wheels turned to the left. unplug put a 7/8 s wrench on it to turn it out, it sould take a bit of muscle it will be tight. put the new one in and torque it to spec. if no torque wrench if you hold a ten pound weight in your hand for five minutes then tighten it to the feeling you have in your arm it should be fine. very easy to change as long as you can get under the car. good luck. it took me fifteen seconds to change mine Friday and have not had a code since. now according to the manual it may come on three times while it learns what a knock is again. mine did. then just make sure you keep high octane fuel higher than92 octane and you should never see the code again. Hope this helps. sensor cost me 42.00 pretty salty for what it is. but it does have a function. Happy Vetting my friend!
Re: The service engine soon light is on..how do you check the codes? (15/15)
 8/18/12 11:46pm
TEN A C
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Posts: 34

Thanks for all of your help.  I have enough info when I take it to the shop.  The guys at the shop are very reasonable and I can usually tell them what I need and they'll take care of it.  I want be doing this one myself....Unhappy
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