ODBII Scantool

Status: Complete

This project involves building an OBDII scantool based on the ELM327 chip from Elm Electronics. I am using the demo board and will make my PCB from the pattern provided.


April 23, 2007

Ordered parts

April 24, 2007

Etched PCB


April 25, 2007

I cleaned the toner from the PCB and polished the copper with some 600 grit sandpaper. The search is on for the proper drill bits. It looks like Harbor Freight may have what I need and there is a retail store about 15 minutes from work so I’ll swing by there and check.

April 26, 2007

Harbor Freight did have a mini-drill set on the cheap so I am in business. The holes are drilled and I spent a couple of hours with the soldering iron to get the board populated. All that remains is a power test and then inserting the chips (which are on order). The fine folks at Elm Electronics are on vacation so my chips probably won’t ship until Monday or Tuesday. That should give me enough time to check the board for mistakes.


April 28, 2007

My ODBII cable arrived from obd2cables.com so I did a quick smoke check with no ICs inserted. All the voltage points checked out and nothing got warm so hopefully I will have a functioning board when the ELM327 arrives.

May 5, 2007

The chips from ELM Electronics arrived today. After inserting the chips I tested basic communication with a PC. Nothing was being returned to the PC but it was obvious that the ELM chip was responding to commands. Close inspection revealed a solder bridge that had destroyed Q8, the transistor responsible for transmitting serial data back to the PC. I fixed the solder bridge, replaced Q8 and voila! A quick trip out to the garage and… no-go talking to the 1998 Oldsmobile Bravada. Thinking that perhaps only part of the circuit was malfunctioning I hooked it up to the 2005 Toyota Camry and had successful communication. Another trip down to the basement and some checking with a multimeter revealed a hairline crack in the trace that provides the J1850 Bus + connection. I quickly soldered that and had success talking to the Bravada. Yay! All that is left to do is put the PCB in a protective case.

July 19, 2007

I successfully diagnosed and repaired a short in the wiring harness of my 1998 Oldsmobile Bravada using this tool. The tool allowed me to determine the error codes that were causing the check engine light to come on. I eventually tracked the trouble to two oxygen sensors. One was malfunctioning and another had a wire grounding out near the exhaust manifold.