2003 Trailblazer- IPC Class 2 Serial troubleshooting tips

RHenningsgard · April 2, 2012

All,

I've had a nightmare with my 2003 Trailblazer since 2009. It's had about half the modules replaced by a service shop and a Chevy dealer, to no avail. It has the same problem it's had since 2009: Voltmeter slides down to about 12 volts, a couple minutes later the Security light comes on, and anywhere from a minute to never later, all of the gages go into wild swings. Power down/power up clears it.

I have decided to troubleshoot the problem myself. It's highly intermittent... so much so that the Chevy service manager used it for a couple of weeks to commute 20 miles each way to work, and never saw the failure. I just took the vehicle back, and it failed within a day, after 70 miles of driving.

I am an electrical engineer, so have no fear of working on the electronics. Getting information is pretty tough, though.

Any pointers, anybody?

Thanks,

Rob---

txab · April 2, 2012

Get service manuals with schematics

Several people have reported problems with the battery cables being bad. Replacing them solved their strange electrical problems. Has this been checked/done on your vehicle?

ChevyTech77 · April 2, 2012

X2 on the battery cables. Measure the voltage drop across them while cranking the engine with the fuel injectors disabled (so it doesn't start). Replace any cable that measures over 200 mv of drop.

RHenningsgard · April 3, 2012

Wow... battery cables. How many times have I seen technicians chase the most exotic problems which end up having the very simplest of causes. I'll get a price on them and swap them out on speculation if they're not too pricey.

Thanks, guys!

P.S. Last night, I designed a remotely-switchable repeater that I can insert into any serial line, and remotely enable/disable the serial signal propagation in either or both directions. Maybe now I won't need to build it.

RHenningsgard · July 9, 2012

YOU NAILED IT! I finally got it fixed. I told the dealer about your recommendations, and as they were completely out of ideas, they very willingly went along. They measured an intermittent 400+ millivolt drop between the negative battery post and the engine block. When they went to replace "engine ground A to battery" the main lug broke off. They replaced a $2.25 bolt, and my truck, which had been failing intermittently since 2007, has been perfect ever since. Thanks a million for your postings!