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I have an ’01 silverado. a while back the oil pressure gauge started going nuts at idle. needle moving way faster than it’s possible for pressure to fluctuate. I figured it was a bad oil pressure sender and just haven’t got around to look at it.
More recently, I’ll be driving down the road and the whole instrument cluster will go nuts. The LCD will flash security, then battery, the ABS, the brake, and the fasten seat belt lights will come on. The fuel and temp gauges will go all the way to E and Cold respectively. The Dash won’t tell what gear it’s in….you get the idea. Only things that work is the speedometer and oil pressure gauges.
usually if I stop and turn the truck off, then back on, the condition will clear and I can go about my day.
I have no clue what this would be caused by. Bad ground maybe? Hopefully not a computer problem
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I would be checking the ground wires first. The side terminal battery cables are notorious for corrosion issues and getting loose over time but the issue could be any of the grounding straps or cables. The first thing that people usually notice when the grounds get bad is the dash going crazy so I am pretty sure that this is a classic ground issue case. If you disconnect the battery make sure that you have the code to unlock the stereo before you do it. If it has the Delco theftlock system you will not be able to use the stereo without the code when you hook the battery back up. If you don’t have the code you can connect a second power supply at the jumper terminals under the hood so the computer and stereo don’t lose power. Just make sure that those connections are good before you unhook the battery if you choose this option. Hope this helps and keep us posted.
Thanks for the reply, I was actually thinking it was possibly a gnd issue myself, glad to know I’m (probably) headed in the right direction. Thanks again
Based on the infrequency of the problem it may be a control unit or logic problem. Meaning it may be the cluster itself and it would need to be replaced. If that’s the case you would need to isolate that unit to be sure the problem was within it and not the result of a failure somewhere else. I think a good start however would be to track down a wiring diagram and check the power and grounds going to the cluster to see if they are good to further your diagnosis. You might be able to find that wiring diagram here.
I’ve finally figured it out and wanted to post the solution so there’s a complete topic with resolution. I cleaned every ground I could find but that didn’t resolve the issue.
I thought the instrument cluster was bad, so I looked into getting one rebuilt. The company I told what the issue was said that on GM vehicles the LCD screen, fuel, temp, and some of the indicator lamps are driven off the class II data bus. The tach, speedo, oil pressure, and volt meter are separate inputs. Bingo! That described my issue perfectly. I got a wiring diagram and found all the modules that interface with the class II data bus. They all go to a central splice point so you can remove modules to eliminate a module and the wire to it as the culprit. I knew my ABS controller had an intermittent issue, and since it was on the class II bus I unplugged it. Prior to unplugging the EBCM the issue was happening about every time I drive the truck. I’ve driven the truck for several hours now over two days and haven’t had a single failure of the IPC.
For those of you who are interested, here’s the technical reason for the failure: The data bus in a modern car is shared by the various control modules. It’s a pulsing signal with 0vdc for a “0” and 5-6vdc for a “1”. The pulses happen so quick a DMM can’t measure it. you need an oscilloscope to “see” the signal. during a a failure of a wire, such as short to gnd, or a failure of a module can “suck” the signal level to 0 on the bus causing other modules to have issues when they don’t get serial data. My truck has very few modules, and the PCM and BCM have a redundant link between them, which is why the truck ran great otherwise.
I plan on taking the EBCM out and shipping it to module masters to be rebuilt since a new one is $800+ from the dealer.
Great find! I suspected you had a control unit problem and I’m glad you were able to find it. If it were some other type of electrical problem it’s likely it wouldn’t be so consistent in the way it acted up. Bad control units usually do that sort of thing. Keep us posted on how that EBCM rebuild goes.
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