OBD II Doesn't Work

n4hmr · March 24, 2016

Hello -

First post on GM-Trucks; hope I'm in the right forum.

I'm in Charlotte, NC, and have a 2002 Chevy Silverado 3500 tilt bed (cab & chassis frame), VIN 1GBJC34U22F129260 and a 6.0L gas engine. I have two electrical problems - OBD II doesn't work & a fuel gauge issue (front and rear tanks). Need OBD II to diagnose the fuel issue.

An instructor at CPCC (Central Piedmont Community College) told me that the pinouts on the OBD II connector are as follows:

4 & 5 are gnd, 16 is power, 6&14 are high speed bus (CAN bus - Control Access Network?), 2 and/or 3 are low speed bus. Does this sound right?

The pins present are in positions 2, 4, 5 14 & 16. I measured ground on 4&5 but found no +12vdc on 16. Didn't scope the other pins yet.

I have a GM Service DVD but cannot find any schematics on the OBD connections. Can anybody tell me where the +12 sources from on Pin 16 (if that is the right pin)? Or how to trace it back? Or how to find that in the Dingbat SPO program?

Any and all help will be muchly appreciated!

Fred

cjb321 · March 24, 2016

check the cigarette lighter fuse. obd2 port didnt work either when i bought my truck and the guy at auto zone told me to check the fuse and sure enough it was blown , after replacing it obd2 worked again.

txab · March 24, 2016

check the cigarette lighter fuse. obd2 port didnt work either when i bought my truck and the guy at auto zone told me to check the fuse and sure enough it was blown , after replacing it obd2 worked again.

+1

Formulabruce · March 24, 2016

+2. You may also end up having a GM power scan plugged it, which is much faster and can operate anything in the truck if the ecu is alive.

n4hmr · March 25, 2016

Yo Chris -

Bingo! Checked the volts on the cigar lighter - nada. Popped the fuse out - blown. New fuse, all works - except for the Dang fuel gauge issue.

For anyone that wants to know, I plowed back into my Service DVD, and finally discovered that they don't refer to this as the OBD connector - they call it the 'Data Link Connector'! Nice. I suppose there's some sensibility to that. I then reviewed all the wiring diagrams and found that connection under

'FIGURE 12. AIR, RTD, RADIO, RDO AMP, ECM B, FRT HVAC, and CIGAR Fuses©' over on the RH side of the diagram. They were nice enough to show that spur leg power went to Pin 16 of the connector, so that confirmed that.

Interestingly enough I found another wiring diagram that showed the same cigar lighter circuit but that one made no mention of the connection to the 'Data Link connector' Go figure.

Note: Used my scanner and found no DTC's other than a misfire on cylinder 2 - which had been diagnosed manually by a GM tech friend Scott and fixed the previous weekend - bad coil.

I am going to close this post and open up a new one for the fuel gauge issue.

See '2002 Silverado 3500 Fuel Gauge Screwing Up'

Thank for the help!

Fred

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231thomas · March 22, 2020

On 3/23/2016 at 8:41 PM, n4hmr said:

Hello -

First post on GM-Trucks; hope I'm in the right forum.

I'm in Charlotte, NC, and have a 2002 Chevy Silverado 3500 tilt bed (cab & chassis frame), VIN 1GBJC34U22F129260 and a 6.0L gas engine. I have two electrical problems - OBD II doesn't work & a fuel gauge issue (front and rear tanks). Need OBD II to diagnose the fuel issue.

An instructor at CPCC (Central Piedmont Community College) told me that the pinouts on the OBD II connector are as follows:

4 & 5 are gnd, 16 is power, 6&14 are high speed bus (CAN bus - Control Access Network?), 2 and/or 3 are low speed bus. Does this sound right?

The pins present are in positions 2, 4, 5 14 & 16. I measured ground on 4&5 but found no +12vdc on 16. Didn't scope the other pins yet.

I have a GM Service DVD but cannot find any schematics on the OBD connections. Can anybody tell me where the +12 sources from on Pin 16 (if that is the right pin)? Or how to trace it back? Or how to find that in the Dingbat SPO program?

Any and all help will be muchly appreciated!

Fred

Fred check your grounds. I've ran into this before

davester · March 22, 2020

...just a note, but if you read the post right before yours, Fred posted that he did fix the problem (which was the common fix for this issue, the fuse for the circuit had blown).