Ok my buddies truck the OBII reader does not work...Has power to pin 16 on plug...no blown fuses at either cig or aux....But the plug confuses me. has pins on 2,4,5,16 but that is it....Does anybody know if that is correct and any other ideas why the reader cant link...works fine on his wifes Tahoe but not on his 2003 Silverado pickup....Help..... by the way pin 16 is getting voltage, but suspect pin 2 is the signal line and might not be sending a signal...Help

 

wow, was hoping that someone new something about this on this forum, does anybody have wiring diagrams that could at least look and see how the diagnostic plug is wiring in the system?

 

Welcome to the forum. You seemed like you knew what you were doing. The connector pinout is correct which you can search for on the web. What OBD reader is it (make, model, S/W version)? What do you get when you try to connect? What year is the Tahoe on which the reader works?

 

I used Acton reader and a more powerfull one from Harbor Freight.Model 94217) which is Can OBD2/EOBD complient. Both readers failed on the truck...the Tahoe is a 2002...Any thoughts? by the way both readers work fine on a 2005 ford f150 and Lexus RX400h....

 

Make sure pin 16 has battery voltage and pin 5, ground. The easiest way to measure the voltage is across the two pins with a multimeter, with key off. Then, make sure pin 5 has continuity to ground (either pin 4 or known good ground). If they check out good, pin 2 is not seeing any Class 2 data for some reason. The Class 2 data bus uses the single-wire VPW J1850 protocol. Physically the data wires from modules on the bus are spliced together which makes it susceptible to an errant module corrupting the bus. If there are problems with the vehicle electronics, your buddy should consider taking it in for service.

 

Ok, thanks for the info, I too discovered the VPW protocol. I put my " scan guage"(I use this on my truck to measure tranny temp etc) on his truck and it read and there are no codes....However the ABS light and after 5 seconds the Brake light is on after starting the car...I reseated the plugs on the ABS unit under the truck and measured 12v to that unit...My Scan guage doesnt measure abs codes so We are stuck unless somebody has some ideas about the sequence of those two light on. He also cannot turn on the Traction control system, however before we unplugged the battery he could. The sequence now is turn ign on, all lights work, turn engine on and the abs stays lit, and the brake light goes out for about 3 to 4 seconds and comes back on. The rear brake lights do work....Anybody experience this.????? Please note: he measured both ABS sensors at the front wheels and got the desired results when spinning the wheels and reading the signal....

 

What was the reason for unplugging the battery?

 

I asked him to do that and turn headlamps on to clear all codes and see what came back up....The traction light went out, and the two other lights remained....I know on the Lexus, Toyota, and Ford sites we do that to try to simplify what exactly we are dealing with...if the fault is really there it will remain.

 

Then, I guess I still don't get it. What exactly was the concern that started this whole mess? And, was the battery unplugged and then plugged back in with key on which could possibly create voltage fluctuations?

As for the present concern, the BRAKE, ABS, and TC warning indicators briefly turn on during the lamp test with key on. Then, all three turn back on after the vehicle is started. Am I getting this right? Is there a "SERVICE BRAKE SYSTEM" warning displayed in the DIC as well?

 

The only indicators on while the car is running is the ABS and check brake lamp. They will not clear....my friend is concerned because he has a smog check in 3 weeks...But I dont think they will fail him for these lights, however something is wrong... The reason to unhook the battery is to try to clear any codes that are in the ecm, since the readers we have are not VPW complient. I was hoping that the lights would reset, but they didnt.