How To Check Obd1 Codes With A Paperclip
(Last Updated On: October 4, 2020)

If you have a GM car from 1980 to 1995 then there is a major chance that you have the OBD1 connector (ALDL).

OBD1 connectors are special connectors that apply to Pontiac, Oldsmobile, Chevrolet, GMC, Cadillac, and Buick vehicles.

While these connectors are older, the great thing about them is that you can easily read these codes without any diagnostic tools.

So, while there are many special diagnostic tools that can read these connector codes, using a diagnostic tool is not entirely necessary.

In fact, to can check ODB1 codes, all you need is a paperclip. Let’s see how you can check Obd1 codes with a paperclip. It’s a great way to read your trouble ODB1 codes for free!


Steps To Check ODB1 Codes With A Paperclip

It’s easy to check ODB1 codes with a paperclip. In fact, you can do it in just 3 quick steps.

Here’s the quick 4-step illustration to check your ODB1 codes with a paperclip:


1. Fin A Paperclip

Most people have paperclips thrown down around their house. Find a paperclip and bend or form it according to your diagnosis box.

odb1 paperlcip


2. Insert Into Test Terminal

First, ensure your engine is off.  Once the key is off, attach the paperclip to both ends of the test terminals A and B (where you would normally place jumper wires):

odb1 terminals

  • A = Ground
  • B = Diagnosis Terminal

When in place, securely, turn key clockwise without starting up your engine.

In this state, the system will enter diagnostic mode.


3. Check and Write Down The Codes

Now that the system is in diagnostic mode, its time to check the codes. In this mode, the vehicle’s computer will display a Code 12, three consecutive times.

It will do this by flashing the “CHECK ENGINE”, “SERVICE ENGINE SOON” or “MALFUNCTION INDICATOR LAMP” or light.

check odb1 codes for free

What is a Code 12? A Code 12 consists of one flash, then one short pause, then two flashes in rapid succession. as such, it should be easy to identify.

After Code 12 is displayed, its time to look for specific trouble ODB1 codes. These codes will be displayed by flashing the “CHECK ENGINE”, “SERVICE ENGINE SOON” or “MALFUNCTION INDICATOR LAMP” light. These codes are all displayed 3 times each and then a code 12 will repeat.

The last step in reading the codes is to simply write down the codes and fix the issue with the vehicle.

Here are the ODB1 trouble codes:

12 – System normal

13 – Oxygen sensor circuit open

14 – Coolant sensor high resistance or shorted

15 – Coolant sensor circuit low or open

16 – Direct ignition system (DIS) fault in the circuit

17 – Camshaft position sensor fault

18 – Crankshaft or camshaft sensor error

19 – Crankshaft sensor circuit fault

21 – TPS sensor out of range

22 – TPS sensor signal voltage low

23 – Intake air temp sensor out of range, low

24 – Vehicle speed (vss) sensor circuit fault

25 – Air temp sensor out of range, high

26 – Quad-driver module (computer) circuit #1 fault

27 – Quad-driver module (computer) 2nd gear circuit

28 – Quad-driver module (computer) circuit #2 fault

29 – Quad driver module (computer) 4th gear circuit

31 – Camshaft position sensor fault

32 – EGR circuit fault

33 – Map sensor signal out of range, high

34 – Map sensor signal out of range, low

35 – Idle air control sensor circuit fault

36 – Ignition system circuit error

38 – Brake input circuit fault

39 – Clutch input circuit fault

41 – Camshaft sensor circuit fault, ignition control circuit fault

42 – Electronic spark timing (EST) circuit grounded

43 – Knock sensor or electronic spark control circuit fault

44 – Oxygen sensor lean exhaust

45 – Oxygen sensor rich exhaust

46 – Pass-key II circuit or power steering pressure switch circuit fault

47 – PCM data circuit

48 – Misfire diagnosis

51 – Calibration error, mem-cal, ecm or eprom failure

52 – Engine oil temperature circuit, low temperature indicated

53 – Battery voltage error or egr or pass-key II circuit

54 – EGR system failure or fuel pump circuit low voltage

55 – Converter error or pcm not grounded or lean fuel or founded reference voltage

56 – Quad-driver module #2 circuit

57 – Boost control problem

58 – Vehicle anti-theft system fuel enable circuit

61 – AC system performance or degraded oxygen sensor signal

62 – Engine oil temperature high temperature indicated

63 – Oxygen sensor right side circuit open or map sensor out of range

64 – Oxygen sensor right side lean exhaust indicated

65 – Oxygen sensor right side rich exhaust indicated

66 – AC pressure sensor circuit low pressure

67 – AC pressure sensor circuit or a/c clutch circuit failure

68 – AC compressor relay circuit failure

69 – AC clutch circuit head pressure high

70 – AC refrigerant pressure circuit high

71 – AC evaporator temperature sensor circuit low

72 – Gear selector switch circuit

73 – AC evaporator temperature circuit high

75 – Digital egr #1 solenoid error

76 – Digital egr #2 solenoid error

77 – Digital egr #3 solenoid error

79 – Vehicle speed sensor (vss) circuit signal high

80 – Vehicle speed sensor (vss) circuit signal low

81 – Brake input circuit fault

82 – Ignition control (IC) 3X signal error

85 – Prom error

86 – Analog/digital pcm error

87 – Eprom error

99 – Power management


4. Reset The Codes

Once you have read the codes and fixed the problem, its time to reset the codes. To clear the codes, simply pull the fuse for about 15-30 seconds.

This process will reset the ECU. be careful not to yank your battery’s negative terminal.

Finally, just to ensure that the problem is properly fixed, drive the car around the city for 75+miles or on the highway for 150+ miles.

Once you have done that,  see if the code pops back up with the paperclip method. If it does not, that means you are good to go!


Still Want An ODB1 Scanner?

If you are insistent on getting an ODB1 scanner, then here are the bets ODB1 scanners on the market:

Actron CP9690 Elite AutoScanner Kit Enhanced OBD I and OBD II Scan Tool

INNOVA 3145 Ford Digital OBD1 Code Reader


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