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.
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):
- 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.
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: