If you have an OBD 1 car (1995 or newer) here is how you check the trouble codes.... you do not need a scanner.
First.... find a paper clip, a notepad, and a pen.
Locate your ALDL connector under your dash (it should be under the steering wheel). it looks like D shaped connector. It's the same connector you plug a scan tool into.
Make sure the ignition is off.
Take your paper clip and ground terminal A and B together (they should be the 2 pins on the far upper right of the connector) they are right next to each other.
Turn the ignition ON, but dont start the car.
The CEL (check engine light, or service engine soon light) will start to flash after a few seconds.
Here is the somewhat tricky part.... understanding the flashing.
The light will flash 2 digit numbers..... IE
one flash.... short pause..... 2 flashes = 12
2 flashes, short pause..... 3 flashes = 23 and so on.
The first and last code will always be 12..... use this to know when the cycle is complete..... it will loop continuously.
Also.... each code will repeat 3 times with a long pause inbetween.
IE
lets say have have a code 19 and a code 24 stored in the system..... this is what you'll see.
one flash, short pause, two flashes, long pause (repeated 3 times)
one flash, short pause, nine flashes, long pause (repeated 3 times)
two flashes, short pause, four flashes, long pause (repeated 3 times)
one flash, short pause, 2 flashes, long pause (repeated 3 times)
and then the cycle wil repeat itself until the ignition is turned off.
Write down the numbers as you read them, and when finished... turn of the ignition and remove the paper clip...
Then you can compare the trouble code number to the cause on the list below.
In order to clear the codes.... you can remove your negative battery terminal for about 15 to 20 minuts, although once the problem causing the code is fixed... the computer will usually clear the code by itself.
GM common codes for OBD1 (for vehicles made before 1995)
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 circuit
17 cam position sensor fault
18 crank or cam sensor error
19 crank 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 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 cam 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 cam sensor circuit fault, igntion 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 ps.pressure switch circuit fault
47 pcm-bcm data circuit
48 misfire diagnosis
51 calibration error, mem-cal, ecm or eeprom 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 a/d converter error or pcm not grounded or lean fuel or frounded reference voltage
56 quad-driver module #2 circuit
57 boost control problem
58 vehicle anti-theft system fuel enable circuit
61 a/c 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 a/c pressure sensor circuit low pressure
67 a/c pressure sensor circuit or a/c clutch circuit failure
68 a/c compressor relay circuit failure
69 a/c clutch circuit head pressure high
70 a/c refrigerant pressure circuit high
71 a/c evaporator temperature sensor circuit low
72 gear selector switch circuit
73 a/c 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 ecm error
87 eeprom error
99 power management
