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How to scan trouble codes

Tiny
MONTANAGUY40691
  • MEMBER
  • 1994 OLDSMOBILE CUTLASS
  • 3.4L
  • V6
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
My car has a service engine soon light on. The scanner port is the same shape as an obd1 scanner but the two pins on the scanner that are close together are side to side and on my car the two pin terminals are up and down. I was told about it being a obd1.5, but I cannot find one that I can buy and the obd2 scanner does not have the same shape plug.
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Thursday, June 28th, 2018 AT 4:07 PM

14 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good evening.

Following is some information on pulling the codes without a scan tool.

Roy

FLASHING DIAGNOSTIC TROUBLE CODES WITH 12 PIN DATA LINK CONNECTOR (DLC)
Due to software changes and the removal of the diagnostic enable circuit (by using 16 pin DLC), Diagnostic Trouble Codes (DTCs) may no longer he obtained by grounding "A" to "B" at the Data Link Connector (DLC). The use of a Tech 1 scan tool or equivalent will be needed to obtain both curent and history DTCs. If the vehicle has a 12 pin DLC that contains a pin "B" then flashing codes MAY be possible by following this procedure.

Although it is recommended that a diagnostic scan tool be used to read diagnostic trouble code(s), it may be possible to flash trouble codes on certain vehicles equipped with a 12 pin DLC. The DLC terminal "B" (diagnostic terminal, if equipped) is the second terminal from the right of the DLC's top row. The terminal is grounded by connecting it to terminal "A" (internal PCM ground), the terminal to the right of terminal "B" on the top row of the DLC.

Once terminals "A" and "B" have been connected, the ignition switch must be moved to the "ON" position, with the engine not running. At this point, the Malfunction Indicator Lamp (MIL) (Service Engine Soon/Check Engine) should flash Diagnostic Trouble Code (DTC) 12 three times consecutively. This would be the following flash sequence: "flash, pause, flash-flash, long pause, flash, pause, flash-flash, long pause, flash, pause, flash-flash." DTC 12 indicates that the diagnostic system is operating. If DTC 12 is not indicated, a problem is present within the diagnostic system itself, and the Diagnostic System Check should be performed.

Following the output of DTC 12, the MIL (Service Engine Soon/Check Engine) will indicate a diagnostic trouble code three times if a diagnostic trouble code is present, or it will continue to output DTC 12. If more than one diagnostic trouble code has been stored in memory, the diagnostic trouble codes will be output from the lowest to the highest, with each diagnostic trouble code being displayed three times.

INTERMITTENT MALFUNCTIONS INDICATOR LAMP
In the case of an "Intermittent" problem, the Malfunction Indicator Lamp (MIL) (Service Engine Soon/Check Engine) may light and then go out. However, the corresponding diagnostic trouble code will be stored in the memory. When unexpected diagnostic trouble codes appear during the diagnostic trouble code reading process one can assume that these diagnostic trouble codes were set by an intermittent malfunction and could be helpful in diagnosing the system.

An intermittent diagnostic trouble code may or may not reset. If it is an intermittent failure. A Diagnostic Trouble Code (DTC) Chart should NOT be used. Consult the "Diagnostic Aids" for the diagnostic trouble code chart corresponding to the intermittent diagnostic trouble code. Diagnosis by Symptom also covers the "Intermittents." A physical inspection of the applicable sub-system most often will resolve the problem.
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Thursday, June 28th, 2018 AT 4:51 PM
Tiny
MONTANAGUY40691
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  • 9 POSTS
How do I know if the scan tool is a tech 1? I have a cen-tech obdII/EOBD and a simple LED obdII scanner if one of these would work then all I need is the cable adapter right?
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Thursday, June 28th, 2018 AT 5:22 PM
Tiny
ASEMASTER6371
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There is no adapter from obd 2 to obd 1.

You need a real scan tool that can read obd 1 systems. Your readers are for obd 2 only.

It does not have to be a tech 1. That is just what they recommend. I used a Snap On MT2500 or what they called the brick.

Roy
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Thursday, June 28th, 2018 AT 5:26 PM
Tiny
MONTANAGUY40691
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Why is it that I can buy an obd1 scanner for 1986-1993 for $30.00 and an obd2 scanner for newer vehicles for $110.00 but there is not one for a 1994 without breaking the bank. Also, there is an adapter from a 16 pin to a 12 pin.
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Thursday, June 28th, 2018 AT 5:34 PM
Tiny
ASEMASTER6371
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1994 is a different scanner and I guess no one manufactured a simple one. The advanced ones will read it.

As far as the adapter, be careful, it may only read up to the 1993 and then you will be out the money for the adapter.

Roy
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Thursday, June 28th, 2018 AT 5:37 PM
Tiny
MONTANAGUY40691
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I love this car but trying to find out what is wrong with it has tempted me to send it to the crusher.
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Thursday, June 28th, 2018 AT 5:40 PM
Tiny
ASEMASTER6371
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Do not do that.

Why not take it to a shop that has the scan tool and have them read the codes for you. I was just looking at the adapters and saw the ratings were terrible for the adapters.

Once they read the codes then let us know the results and we can help guide you through the process.

Roy
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Thursday, June 28th, 2018 AT 5:43 PM
Tiny
MONTANAGUY40691
  • MEMBER
  • 9 POSTS
I have to tow the car to a shop. It runs great until it has warmed up the the engine surges and stalls. The service engine soon light only comes on after it begins surging. I have always done the work myself except this car because I cannot read the code. So many places will try to rip you off.
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Thursday, June 28th, 2018 AT 5:48 PM
Tiny
ASEMASTER6371
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Try this.

With the engine idling, tap on the ECM and see if it stutters and stalls. The early ECM has board issues where they cracked and caused this type of issue.

Roy
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Thursday, June 28th, 2018 AT 5:51 PM
Tiny
ASEMASTER6371
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Do the same thing to the mass air flow sensor as well.

Roy
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Thursday, June 28th, 2018 AT 5:52 PM
Tiny
MONTANAGUY40691
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Well it started small with misfires for a while and progressively got worse until it started stalling. After it stalls and you try to restart the car there is no response the starter does not even try to turn. You have to reset the system by disconnecting the battery. If you keep on the gas while it is surging and trying to stall all the gauges go haywire.
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Thursday, June 28th, 2018 AT 5:55 PM
Tiny
MONTANAGUY40691
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But it only does this when the car's thermostat opens about the third time.
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Thursday, June 28th, 2018 AT 5:57 PM
Tiny
MONTANAGUY40691
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I have replaced the O2 sensor, cam shaft sensor, checked all wire that were exposed to heat, cleaned out the EGR passage, and replaced the EGR.
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Thursday, June 28th, 2018 AT 6:05 PM
Tiny
ASEMASTER6371
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Did you try what I suggested with the ECM and the mass air flow?
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Friday, June 29th, 2018 AT 4:38 AM

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