Pulling trouble codes...

bowtie_pasta · January 22, 2003

Does anyone know how the home mechanic would pull the trouble/diag codes on this truck?

I keep getting an intermittent CHECK ENGINE light and want to know what it's reporting.

Thanks

bowtie_pasta · January 22, 2003

Ok, I found this info. Can anyone explain in more detail how to read these codes? My truck is an 85', so I don't know if the 86' had any significant changes (I doubt it).

"Chevy Trouble Coding

Q:The Service Engine Soon light comes on when I'm driving my '86 Chevy S-10 Blazer. The service manual says there's an "ACLR module" from which I can jump A to B to receive a code isolating the problem. The book, however, says on one page it's located underhood on the left side of the firewall and on another page that it's under the dash. Neither shows a picture of the box. Can you help me locate it?

A: Jumping A to B takes us way back. The correct terminology is "ALCL Connector" (Assembly Line Communication Link), which is located under the driver's side of the instrument panel. If it's not plainly visible, someone must have unbolted it and left it hanging around under the dash somewhere. The ALCL is a 12-cavity connector labeled A through M, but leaves out the I. With the ignition on, jump terminal A to B (a paperclip will work just fine). If the Electronic Control Module is functional then the Service Engine Soon light will flash a Code 12 three times (flash-pause-flash-flash x 3). The trouble codes, stored in the memory, will present themselves in the same manner going from lower to higher numbers. Write the codes down and find the appropriate diagnostic chart in whatever service manual you're working with. Always start with the lowest-number trouble codes first. The first repair may correct the higher codes at the same time. This is the old-fashioned way. A quality scan tool will plug into the ALCL and immediately give you the stored trouble codes along with a multitude of additional information to aid in the diagnosis of a problem. Happy hunting."

carguru · January 22, 2003

Routine should work fine for '86 model and all other OBD1 cars and trucks. '96 up OBDII will require scanner. The codes are retrieved by shorting the 2 pins mentioned on the diagnostic port. The check engine light will flash the code. Jot the code down and hunt through the codes that match the trouble code. Diagnostic port should be located near the bottom of the dash just under the steering column. Good luck. :thumb:

bowtie_pasta · January 23, 2003

So would I be expecting to see actual numbers flash on the dash? This is what's confusing me. Or do I have to count the number of flashes?

Thanks

carguru · January 23, 2003

You will have to watch and count the service engine light flash the stored codes. It will always flash the 12 code first. Then whatever stored trouble code will be flashed. The alternative is to pick up one of the OBD1 scan tools. Hope this helps.

bowtie_pasta · January 23, 2003

Ok, I think I understand it now. Here is an example, tell me if I'm right or wrong:

Code 25 would equal = flash-flash-pause-flash-flash-flash-flash-flash

Thanks again carguru!

carguru · January 23, 2003

Yep, sounds like you got it. :thumb: Good luck.

mnstrmdnss · January 24, 2003

i can help you out one step further.

all GM OBD1 dtc's listed below

code no.

12 (1)...............no rpm referenece pulse(koeo)

13...............................O2 sensor circuit open

14........coolant temp sensor signal voltage low

15........coolant temp sensor signal voltage high

21...............................tps signal voltage high

22................................tps signal voltage low

23....................MAT sensor siganl voltage high

24................................................VSS

25....................MAT sensor signal voltage low

32...................................EGR system error

33....................MAP sensor signal voltage high

34....................MAP sensor signal voltage low

35....................................IAC idle speed error

36.........idle speed actuator fault(A/T, FULL SIZE)

42.........................EST circuit open or grounded

43...................................................ESC error

44..............................lean exhaust indication

45...............................rich exhaust indication

51..................faulty PROM, MEM-CAL OR ECM/PCM

52..................faulty/missing CAL-PAC or MEM-CAL

53.......................................system overvoltage

54..................................fuel pump voltage low

55.............................................ECM/PCM error

66......................................A/C pressure sensor

85................................................PROM error

87..............................................EEPROM ERROR

if you want a flow chart to diagnose each problem, i can get that for you, jsut let me know.

btw, gm obd1 codes are displayed from least no. to highest no., which is NOT the order in which they happen

bowtie_pasta · January 24, 2003

Oh wonderful, thanks so much for the help guys! Maybe I'll try to dig into it this weekend. No telling though because we are getting ready to move into a new home. I might put this project off until we get settled into the new place.

Thanks again.