1989 GMC C1500 no code 12

Tiny
CHUCK921
  • MEMBER
  • 1989 GMC C1500
  • V8
  • 2WD
  • AUTOMATIC
  • 199,722 MILES
Ok this truck has had the computer replaced with a new one(same prom) and it still doz this: high idle, pinging, dies check engine light is on and of the pinging is when you put your foot in it. And with the scanner reads no prob. Found. Can not get the light to blink code 12 if I could get the codes I could out of it then I could fix it HELP! And thankx. I cant afford to donate much to day.
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Tuesday, September 15th, 2009 AT 11:37 PM

10 Replies

Tiny
SERVICE WRITER
  • EXPERT
What liter?

The ECM incorporates a diagnostic program which, when activated, will flash codes stored in the trouble code memory through the "CHECK ENGINE" lamp. A diagnostic connector, located under the instrument panel, is used to activate the self-diagnosis system. The connector, allows access to system circuits and contains a test terminal which, when grounded with the ignition on and engine stopped, causes stored trouble codes to be flashed on the "CHECK ENGINE" lamp.

When the diagnostic terminal is grounded (jumper terminal "A" to "B") with the ignition on and engine stopped, codes are displayed in numerical order, always starting with Code 12 which indicates that the self-diagnosis system is operating properly. Trouble codes, are displayed in the following manner: Code 12 is displayed by one flash, a short pause, then two flashes and a longer pause. Code 12 will be displayed 3 times in this manner, then any additional codes stored will be displayed 3 times each in a similar manner until all codes have been displayed. Once all codes have been displayed. The process will be repeated as long as the test terminal remains grounded. DO NOT ground the diagnostic terminal until the ignition is "ON" and engine is "OFF" (not running). After trouble codes have been noted, the ground wire should be removed from the test lead and the engine should be started. When the engine is started and there are no other codes except Code 12, the "CHECK ENGINE" light should go out after approximately 5.0 seconds, indicating that the ECM has not detected a malfunction. However, if the ECM detects a current malfunction, the "CHECK ENGINE" lamp will remain illuminated while the engine is running. A trouble code indicates a possible system malfunction. If a trouble code can be obtained, even if the "CHECK ENGINE" lamp is "OFF" when the engine is running, a "SYSTEM PERFORMANCE CHECK" should be performed and the indicated circuit should be inspected.
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Thursday, September 17th, 2009 AT 7:06 AM
Tiny
CHUCK921
  • MEMBER
I have read the ans you sent me but. I do not get any codes, check engine light is on but no flash code 12 or any codes.
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Thursday, September 17th, 2009 AT 2:21 PM
Tiny
SERVICE WRITER
  • EXPERT
What liter engine?

Pre-detonation cause be caused by various things including low octane, try going to premium fuel.

Il sent
you a chart.
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-1
Thursday, September 17th, 2009 AT 2:48 PM
Tiny
CHUCK921
  • MEMBER
5.7
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Thursday, September 17th, 2009 AT 8:34 PM
Tiny
SERVICE WRITER
  • EXPERT
Did you get the chart? Sometimes the emails end up in the spam folder. It would be good to get the code problem solved.

Did you look at this page?
http://www.2carpros.com/first_things/why_does_my_engine_idle_high.htm

Are you losing any coolant? A head gasket can fail between 2 cyls and cause a ping.

Incorrect timing can cause a ping.

Excessive carbon build up can cause a ping.

A bad egr valve as well. try unhooking it and see if it changes.

bad knock sensor, unplug and see if it changes.
I believe that system grounds to the therostat bolt. These have a habit of corodeing where the bolt goes in the housing. You can have a good connection to the bolt but not the engine.

A lack of fuel volume or a restricted exhaust such as a plugged cat can cuase pinging, but would not explain the high idle. Premium gas would not explain the high idle, I retract my previous comment on that..

Let me know the progress on getting the codes.
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Friday, September 18th, 2009 AT 5:43 AM
Tiny
CHUCK921
  • MEMBER
I did get the chart and im at : back probe ckt 451. Witch one is that? Exhast good pressure and doz not smell like coolent the cat has been replaced. I think the ecm is cawzing the IAC. Valve to act up. And I did change the valve still the same I think this is the high idle prob. I want to send ya some more money do I start over with same title ( 1989 gmc code 12)?
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Saturday, September 19th, 2009 AT 1:35 PM
Tiny
SERVICE WRITER
  • EXPERT
451 is the white/black wire


http://www.2carpros.com/forum/automotive_pictures/30961_gmc_1.jpg



I'm not sure how the donation works, but keep this thread.
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Monday, September 21st, 2009 AT 5:08 AM
Tiny
CHUCK921
  • MEMBER
Well it looks to be the prom.I will replace the ecm with one out of the bone yard ( with the same part #) and try that. The new prom is 199. Oo, the bone yard ecm is 30. Oo. I will keep in touch with ya and let ya know if I fixed it > Big thankx to all who helped out. If I can help you out with some other car problem, you got my # thankx Chuck
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Tuesday, September 22nd, 2009 AT 9:48 PM
Tiny
CHUCK921
  • MEMBER
Hi guys remember me, well its still the same, with new prom and a new computer no code 12. Well ok 1 flash code 12 then the light goz out. When I get some money ill send you some. Thankx. Chuck
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Monday, October 19th, 2009 AT 11:17 PM
Tiny
SERVICE WRITER
  • EXPERT
Hi Chuck.

Did you try unplugging the egr?

Have you tried any carbon removal procedures?

Paul
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Tuesday, October 20th, 2009 AT 5:52 AM

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