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CAN low voltage too low

426 Views 6 Replies 3 Participants Last post by  brcisna

2010 Chevrolet Suburban idles very rough after AFM/DOD delete,, checked compression all 160 psi even across the cylinders

Bought this truck 'as is' knowing of the rough idle situation. The previous owner after doing the cam lifters replace done the AFM/DOD in ECU delete with the supplied DiabloSport Preditor 2. Stock non DOD cam. AFM Racing deluxe kit
After doing some recent checking my Autel entry level handheld scanner would sometimes view the data stream,,and many times would only show half the available pids. Bought a second cheap OBDII ,usb dongle to try as a backup.This reader does the same. Sometimes read data sometimes does not.Both these units work fine on my old 2003 Suburban,
Yesterday done some voltage and resistance checking at the DLC,and with key on battery voltage 12.6 v ,,CAN high shows 2.55 v ,,but CAN low is only showing 2.1v
Anyone have any ideas how to probe backwards on CAN low network. This voltage does diffinately seem too low.
Visually looking all the ground straps motor to chassis looks connected per the GM wiring schematic i was able to conger up.

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The high speed LAN (GMLAN) will read 2.5 volts at network idle; the low speed (Class 2) will read 7 volts at idle.
Starting the truck should not make any difference in the voltage readings.

As I understand the LAN protocol, the voltage varies as data is transmitting. No data, circuit at idle, the voltage should be 2.5 volts, as data flows, the voltage varies by 1 volt plus or minus on each line of the LAN

Your not going to see the true voltage swings with a meter, not even with a digital meter, you will need a scope.

I believe there is a pair of 110 ohm resistors, if connected in parallel, the net result is 55 ohms; but I don't know how they are connected
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