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CAN low voltage too low

429 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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You need a scope to analyze a good or bad CAN signal.

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There are 2 x 120 ohm terminating resistors on the CAN network so basically they are in parallel. When the network goes to sleep, you can measure the resistance and expect 60 ohms if the module containing the resistors are operational. If one module containing the resistor is dead, you will not get 60 ohms and the CAN signal will be corrupted and your scanner wont be able to link to the network.

Have you looked at updating your scanner firmware? They could be outdated and not able to link to the newer vehicles OBD2 DLC.
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