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89 chevy 7.4 dually code reader


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Hybriddyne
New User

Jun 23, 2013, 7:39 PM

Post #1 of 9 (2247 views)
89 chevy 7.4 dually code reader Sign In

Hello all, I am trying to work on the old tow vehicle and need a code reader. For some reason I cannot find out what code reader I need for my 89 Chevy 1 ton Silverado dually with a 7.4 EFI.


Hammer Time
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Jun 24, 2013, 3:17 AM

Post #2 of 9 (2219 views)
Re: 89 chevy 7.4 dually code reader Sign In

This is OBD1, a simple code reader is for OBD2. You need an OBD1 scan tool.

If all you need is codes (not likely), you can just jump terminals A and B and count the check engine light flashes.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Hybriddyne
New User

Jun 24, 2013, 7:50 AM

Post #3 of 9 (2202 views)
Re: 89 chevy 7.4 dually code reader Sign In

Thank you for the information! I am finally getting somewhere! I tried to do the jumper between pin a and b but cant get the code to start blinking ??? It will only blink once and then the light stays on.


Hammer Time
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Jun 24, 2013, 8:58 AM

Post #4 of 9 (2198 views)
Re: 89 chevy 7.4 dually code reader Sign In

Are you sure you are jumping the right pins. Some vehicle mount the connector upside down.
Make sure it is key on, engine off.







~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Jun 24, 2013, 8:59 AM)


Hybriddyne
New User

Jun 24, 2013, 9:53 AM

Post #5 of 9 (2184 views)
Re: 89 chevy 7.4 dually code reader Sign In

Double checked again even took a meter to verify pin A was to ground and I still cant get it to go into diagnostic mode ??? Any one else out there with this problem ???


Discretesignals
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Jun 24, 2013, 9:59 AM

Post #6 of 9 (2181 views)
Re: 89 chevy 7.4 dually code reader Sign In

What is wrong with the vehicle?





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Hybriddyne
New User

Jun 24, 2013, 4:09 PM

Post #7 of 9 (2160 views)
Re: 89 chevy 7.4 dually code reader Sign In

The Service Engine Light comes on after about 2-4 miles of driving. I have unplugged the battery for a half hour and then reconnected and let sit for 1 hour to assure the computer reset.
If I run the truck in my driveway with out driving it the light wont come on. Soon as I drive it for 2-4 miles the the light come back on.
I just noticed the tail and brake lights are not working ??? Could it be related ???
Thanks for all the tips so far !!! Great forum !!!


Discretesignals
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Jun 24, 2013, 4:38 PM

Post #8 of 9 (2157 views)
Re: 89 chevy 7.4 dually code reader Sign In

The brake and tail lamps being inoperative shouldn't have anything to do with the ECM. Usually when you jump A & B together, the ECM will flash code 12 to tell you that the diagnostic system is operational. If it doesn't flash 12, unplug the TPS sensor while the engine is running to force a code. See if the code 21 appears when you recheck.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Tom Greenleaf
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Jun 28, 2013, 3:50 PM

Post #9 of 9 (2125 views)
Re: 89 chevy 7.4 dually code reader Sign In

You count the blinks which will repeat. Long blinks, short blinks and will do each three times. Convert those to #s. 12 should just mean it's comunicating as DS said but means nothing else. If you keep resetting it you are losing the codes till they return,

T







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