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EagleMark
02-21-2011, 03:37 PM
If your having a Check Engine Light come on then here's a way to check what error code the ECM is reporting. There are some GM explanations and exact step by step ways to troubleshoot at the bottom of this post in a dowloadable PDF document.

Trouble Codes

THE ALDL CONNECTOR:
http://eagle-mark.com/pictures/albums/userpics/ALDL-OBD1-Port.jpg

To Display Trouble Codes:
Run a wire or paper clip from Pin A to Pin B then turn the ignition on but do not start engine. The "Check Engine " light will flash in the following sequence: flash, pause, flash-flash, long pause flash, pause, flash-flash, long pause flash, pause, flash-flash, long pause. This is a code "12" which will always be there and tells that the diagnostic test is working. After this series of flashes and pauses any stored trouble codes will now flash. If you do not see the "12" flash three times, your diagnostic circuit is defective.
Most vehicles will display stored trouble codes, then "12" again.

TROUBLE CODES

12. No reference pulses to Electronic Control Module (ECM). You will get this code when checking for error codes because the engine is not running.
13. Oxygen sensor signal stays lean during warm engine cruise, your O2 sensor could be unplugged or faulty wire.
14. High temperature indicated at engine coolant temp. sensor. Sensor could be unplugged or faulty wire.
15. Low temperature indicated at engine coolant temp. sensor
21. High voltage at throttle position sensor. Sensor could be unplugged.
22. Low voltage at throttle position sensor
23. Low temperature at manifold air temperature sensor
24. Circuit fault in vehicle speed sensor
25. High temperature at manifold air temperature sensor
29. Fault in 4th gear switch
32. Fault in exhaust gas recirculation valve diagnostic switch
33. High voltage (low vacuum) at MAP sensor.
34. Low voltage (high vacuum) at MAP sensor.
41. Cylinder select error
42. Fault at electronic spark timing circuit (sets when timing is set also, clear code and verify that it does not return.)
43. Low voltage at electronic spark timing circuit
44. Oxygen sensor lean
45. Oxygen sensor rich
46. Fault at vehicle anti-theft system
51. PROM error
52. Low voltage at oil temperature sensor
53. High voltage at battery
54. Low voltage at fuel pump OR Low voltage at Fuel pump relay
55. Problem at Electronic Control Module (ECM) - ECM failure OR Serial bus error
62. High voltage at oil temperature sensor

CLEARING THE TROUBLE CODES
Turn the key switch to the off position. To clear any trouble codes, disconnect the battery for 30 seconds or unplug the connectors to the ECM. If this is done at the battery, you may loose your preset stations on your stereo A better place to remove power is at the fuse.

For a more informative diagnostic look at your system you will need a laptop computer, and ALDL cable and a free program called winALDL from here.
http://winaldl.joby.se/

Good luck hope that helps.

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Compliments from dyeager535 for contributing these documents. Its a more complete fuel injection trouble codes and diagnostics. These are all in .pdf format so download and save them on your computer for future reference. Click on the link below, then after it downloads to your computer click on "File" then "Save As" and find a space on your computer. This way you only download once then have the file to use whenever you want even without an Internet connection.

TBI Trouble Codes
http://www.eagle-mark.com/Fuel-Injection/TBIcodes.pdf

TPI Trouble Codes
http://www.eagle-mark.com/Fuel-Injection/TPIcodes.pdf

V6 Trouble Codes
http://www.eagle-mark.com/Fuel-Injection/v6codes.pdf