P0600

P0600 indicates a serial communication link malfunction, meaning the PCM has lost expected data traffic with one or more modules on the CAN, GMLAN, SCP, or CCD bus. Start cheapest-first by scanning every module with a bidirectional tool, not just the PCM, since the missing module is the diagnostic clue. Verify battery voltage at rest above 12.4V and during cranking above 9.6V, because low system voltage is the single most common cause of phantom comm faults. Inspect the data link connector at pins 6 and 14 (CAN-H and CAN-L) with key on, engine off, looking for roughly 2.5V on each leg, and with key off across pins 6-14 you should see approximately 60 ohms (two 120-ohm terminating resistors in parallel). A reading of 120 ohms means one terminator is missing or one module is unplugged; a reading near 0 ohms is a shorted bus. Wiggle-test the harness near common chafe points (firewall pass-through, behind glovebox, near the alternator) while watching live data drop. The expensive misdiagnosis trap is replacing the PCM when the actual fault is a single corroded ground (G102/G104 on GM, G103 on Ford) or a failed module dragging the bus low — that wastes a $900+ part for a $5 fix.

Vehicle-specific patterns: 2003-2007 GM full-size trucks and SUVs (Silverado, Tahoe, Suburban with 4.8/5.3/6.0L) commonly throw P0600 alongside U-codes from a corroded G103 ground stud near the left cylinder head or a failed instrument cluster pulling Class 2 bus low. 2004-2008 Ford F-150 and Expedition show P0600 with U0100/U0101 from chafed CAN wiring at the engine harness pass-through behind the battery tray, addressed in TSB 08-7-6. 2005-2010 Chrysler/Dodge/Jeep vehicles with the TIPM (300, Charger, Grand Cherokee, Ram 1500) frequently set P0600 when the TIPM internal CAN driver fails, a well-documented pattern covered by multiple FCA TSBs and the subject of class-action settlements. 2002-2006 VW/Audi with the convenience-CAN gateway throw P0600 when the gateway module under the driver's footwell loses ground or sees water intrusion from a leaking cowl drain. Estimated repair: $40 to $1,400.