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Username Post: Checking trouble codes for OBD-I (1988-1995 trucks)        (Topic#273660)
Posts: 26167
Age: 44
Loc: Texas
Reg: 08-01-03
12-17-11 10:05 AM - Post#2169725    

Hey gang, I thought I'd throw together a code checking document to replace the outside link to - just a basics on how to check codes, and a simple code list for the common gas-engine stuff. Please let me know what y'all think so I can fine-tune it before replacing the link in our FAQ post. Thanks!


Checking trouble codes on the OBD-I system used in our trucks from 1988 to 1995 is easy and requires no tools other than a paper clip or small scrap of wire for jumpering the A & B terminals on the DLC connector (also known as ALDL) under the driver's side of the dashboard. Here's a picture indicating the A & B terminals at the top right:

● With the ignition switch off, jumper the A & B terminals on the DLC connector.
● Turn the ignition switch on (but do not start engine) while watching the "Service Engine Soon" light on the dash.
● Each code will be represented by the SES light flashing, pausing, and flashing.
● Normal operation begins with code 12, represented by a flash, pause, flash flash indicating "1" and "2" meaning "12".
● Each code will appear 3 times before moving on to the next. Codes display in numerical order.
● When the list of codes has completed, the list will repeat, starting again with 12.
● Code 12 is normal and not an indicator of a problem.

Please note that a code is a starting point and does not necessarily mean the particular sensor or system is bad. Codes can often be caused by other problems and the particular sensor is merely reporting that its data is out of range; it is up to the troubleshooter to determine the cause of the problem.

Codes can be cleared by disconnecting the battery for 20 seconds. Codes will also clear if after 50 starts the problem has not reoccurred.

This is a list of codes relating to gasoline engines. The diesel codes are much more extensive and not listed here. Not all codes apply to all systems. If you have a code not listed, please post for help with it.

13 - O2 (oxygen sensor) circuit open
14 - ECT/CTS (engine coolant temperature) sensor circuit low (high temperature)
15 - ECT/CTS (engine coolant temperature) sensor circuit high (low temperature)
16 - VSS (vehicle speed sensor) buffer fault
21 - TPS (throttle position sensor) circuit high (signal voltage high)
22 - TPS (throttle position sensor) circuit low (signal voltage low)
24 - VSS (vehicle speed sensor) circuit low
28 - TR (transmission range) pressure switch assembly
32 - EGR (exhaust gas recirculation) valve error
33 - MAP (manifold absolute pressure) sensor circuit high (low vacuum)
34 - MAP (manifold absolute pressure) sensor circuit low (high vacuum)
35 - IAC (idle air control) error
36 - Idle speed control actuator error (when equipped)
42 - IC (ignition control) error
43 - KS (knock sensor) error
44 - Lean exhaust
45 - Rich exhaust
51 - PROM (memcal, chip) error
53 - System voltage high (supply to ECM/PCM)
54 - Fuel pump relay circuit low voltage
55 - ECM/PCM error


I'm planning on possibly writing some short "where to start/possible scenarios" for some of the codes as well, since the search engine limitation of 4 character minimum makes searching for specific code #'s practically impossible.

94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects

Low priced Genuine GM Auto Parts
"3rd Year" Silver Supporting Member
Posts: 2057
Loc: Salt Lake City
Reg: 06-20-09
12-17-11 06:00 PM - Post#2169849    
    In response to someotherguy

Nice work, Bro. Great to keep the info alive front and center.

'94 Silverado K2500 4X4 5.7 5spd Xcab LB. SOLD. :-(
'00 Contour SE 2.5 24V

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke

Forum Newbie
Posts: 10

Loc: Puyallup WA
Reg: 03-16-13
03-19-13 05:13 PM - Post#2327822    
    In response to CowboyTrukr

I jumped the fuel pump relay wires gray and orange and now it starts so tomorrow I will buy another fuel pump relay. No codes I found a fusible link that looks bad so I will replace it also thanks for that.

My Birthday Week
Posts: 177

Loc: Hawaii
Reg: 01-21-13
03-20-13 03:30 PM - Post#2328070    
    In response to Adam144

As always Great info...but isn't this in the FAQ?

Posts: 26167
Age: 44
Loc: Texas
Reg: 08-01-03
03-21-13 05:27 AM - Post#2328201    
    In response to HMAJNG

This is the same post from the FAQ; everything in there is either a link to an existing post in the forum, or a link to an outside site.

94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects

Low priced Genuine GM Auto Parts
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