DiagnoseDan tackles a Mercedes GLA no-crank issue and total interior electrical failure after a main dealer incorrectly blamed aftermarket multimedia and ambient lighting upgrades.
The 2017 Mercedes-Benz GLA presented with a drained battery, a no-crank condition, and an ignition that refused to turn off. A vehicle scan showed widespread communication failures alongside fault code U001988, indicating the interior CAN bus was offline.
Using ALLDATA to locate the X30/32 interior CAN potential distributor behind the instrument cluster, Dan connected a PicoScope to the brown and brown-red CAN high and low lines, confirming both wires were shorted to ground at 0V.
Dan isolated the circuit by unplugging modules from the distributor one by one. Activity returned when slot ten was disconnected, which links to the door control modules, revealing a 1.3-ohm short to ground remaining within the wiring loom itself.
Wiggling the harness near the front passenger A-pillar led Dan to a tiny, nearly invisible pinhole in the insulation where the CAN wire was rubbing against a sharp metal chassis ridge. Repairing and rerouting the wire fully restored all interior systems.
