QuestionHello, I have a question on this, I am a mechanic myself for about 12 years and this has me baffled.
Strictly a No Bus, no gauge output with the ABS light on with key on. I know that the BCM and ECU are not on talking terms as the no bus tells me.
I do the key off/on/run while holding the trip odometer button and the gauges pass the test perfectly, each gauge is on top of the check at the right spot.
I tried running alternate grounds from the battery to the body and engine with heavy gauge jumper cables to see if a ground was faulty, but battery was clean and ground made no diff.
OBD2 says , No faults and no codes.
I replaced BCM and ECU and it ran fine still but no gauges, basically no difference. I do notice upon key on that the gauges move just a hair, all except speedo. Just like they get a form of power, just enough to budge them, but not to register at all. Not anything like when I test the panel.
What do ya think? I appreciate any help!
AnswerBUS issues are frequently something totally seperate from a power and ground related issue. The bus goes through numerous modules and while they may all have power and ground, they don't all want to talk well.
In addition, BUS failures are not always conditions that will set a check engine light. The radio is tied in to the BUS but has nothing to do with emissions or engine management. Thus there's no CEL condition set.
Furthermore, because other modules are tied in not all scan tools have the ability to communicate with these modules. The dealer scan tool can obviously talk with all of the modules (when a BUS failure is not present), the latest and greatest SNAP-ON scan tool can talk with MOST of the modules (NOT HVAC on some models which is active on some BUS systems), and then from there things just go down hill. I've got a $1,000+ scan tool that works from a common PDA but it can only talk to some Engine controllers, very few trans controllers, even fewer ABS controllers, and no BCM/Radio/HVAC/Airbag/other modules.
So your ability to communicate with bus-active modules not only depends on whether or not the component is functioning properly but also the quality of the scan tool.
I would unplug the radio, the airbag control module (under the center console), the RKE and the ABS module to see if this frees up the BUS network again. This may set codes, and messing with the Airbag module will require battery disconnects both for plugging and unplugging, but these are about the only "optional" modules that both talk on the bus and will keep the MIC active long enough to see if you've made a change.
Doug
