I have just finished a body off restoration of my 1989 Chevrolet Scottsdale 2500 HD.

My question, is there an OBDI or OBDII or do I need a adapter to scan it?

Even if I rebuilt the engine and transmission it has 90 thousand original miles on it before the restoration. Please let me know if there is a way to use my scan tool.


1989 is OBD1, my favorite scanner for this vintage GM product is a Snap-On MT2500, you can find them on eBay fairly reasonable. Be sure the scanner comes with the GM1 aldl adapter, a Primary cartridge and a Troubleshooter cartridge and cables for your model year.

You can short the proper pins (image below) to get the check engine light to flash any codes stored, do this with Key on, Engine off (KOEO). You will get long flashes and short flashes.

Code 12 means there are no codes stored, One long flash followed by 2 short flashes.

Long flashes are the first digit in the number code, followed by short flashes for the second digit.

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code - code definition

12- diagnostic mode or no codes present

13- 02 sensor or circuit

14- coolant sensor or circuit/ high temp indicated

15- coolant sensor or circuit/ low temp indicated

16- system voltage out of range

19- crankshaft position sensor or circuit

21- throttle position sensor or circuit- voltage high

22- throttle position sensor or circuit- voltage low

23- mixture control (m/c) solenoid or circuit (carbureted models)

23- manifold air temperature (mat) sensor or circuit (1990 and earlier models)

23- intake air temperature (iat) sensor circuit (fuel-injected models)

24- vehicle speed sensor (vss) or circuit

25- manifold air temperature (mat) sensor or circuit - high temperature indicated (1990 and earlier models)

25- intake air temperature (iat) sensor or circuit - high temperature indicated (1991 and later models)

26- quad driver module circuit

27- quad driver module circuit

28- quad driver module circuit

29- quad driver module circuit

31- park/neutral position (pnp) switch circuit

32- baro sensor or circuit (carbureted models)

32- egr circuit (fuel-injected models)

33- manifold absolute pressure (map sensor signal voltage high

33- mass air flow (maf) sensor or circuit - excessive airflow indicated 34- manifold absolute pressure (map) sensor signal voltage low

34- mass air flow (maf) sensor signal - low airflow indicated

35- idle speed control (isc) switch or circuit (shorted) (carbureted models)

35- idle air control (iac) valve/ circuit

38- brake switch circuit 39- torque converter clutch (tcc) circuit

41- no distributor signals to ecm, or faulty ignition module ( carbed models)

41- cylinders select error- mem-cal or ecm problem ( fuel-injected models 41- cam sensor circuit (3.8 engine)

42- bypass or electronic spark timing (est) circuit

43- low voltage at ecm terminal l (carbureted models)

43- knock sensor circuit

44- oxygen sensor or circuit - lean exhaust detected

45- oxygen sensor or circuit - rich exhaust detected

46- power steering pressure switch circuit

48- misfire diagnosis

51- prom, mem-cal or ecm problem

52- calpak or ecm problem

53- egr fault (carbureted models only)

53- system over-voltage (ecm over 17.7 volts)

54- mixture control (m/c) solenoid or circuit (carbureted models)

54- fuel pump circuit (1986 and later models)

55- oxygen sensor circuit or ecm

55- fuel lean monitor (2.2l engine)

61- oxygen sensor signal faulty (possible contaminated sensor)

62- transaxle gear switch signal circuits

63- manifold absolute pressure (map) sensor voltage high (low vacuum detected)

64- manifold absolute pressure (map) sensor voltage low (high vacuum detected)

66- pressure sensor or circuit air conditioning


89 is OBD1 and requires specific connectors and a OBD1 scantool. You can jump pins A & B on the ALDL (Assembly Line Datalink Connector located under the driver side dash) to make the MIL flash out codes.

  • Maybe a link to what the flash codes mean and a definition of ALDL?
    – JPhi1618
    May 10 '16 at 14:53
  • @JPhi1618 I'll add he code definitions later on my phone atm.
    – Ben
    May 10 '16 at 14:58

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